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191 Cards in this Set
- Front
- Back
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Nutrition
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Process by which chemical substances (nutrients) are acquired from the environment and used in cellular activities.
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Essential nutrients
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Must be provided to an organism.
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Essential nutrients:
Macronutrients |
Required in large quantities; play principal roles in cell structure and metabolism.
Proteins, carbohydrates |
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Essential nutrients:
Micronutrients or trace elements |
Required in small amounts; involved in enzyme function and maintenance of protein structure.
Manganese, zinc, nickel |
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Organic nutrients
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Contain carbon and hydrogen atoms and are usually the products of living things.
Methane (CH4), carbohydrates, lipids, proteins, and nucleic acids |
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Inorganic nutrients
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Atom or molecule that contains a combination of atoms other than carbon and hydrogen.
Metals and their salts (magnesium sulfate, ferric nitrate, sodium phosphate), gases (oxygen, carbon dioxide) and water |
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Microbial Cytoplasm
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70% water
Proteins 96% of cell is composed of 6 elements: Carbon Hydrogen Oxygen Phosphorous Sulfur Nitrogen |
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Carbon Sources
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Heterotroph: Must obtain carbon in an organic form made by other living organisms such as proteins, carbohydrates, lipids, and nucleic acids.
Autotroph: An organism that uses CO2, an inorganic gas as its carbon source. Not nutritionally dependent on other living things. |
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Nitrogen Sources
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Main reservoir is nitrogen gas (N2); 79% of earth’s atmosphere is N2.
Nitrogen is part of the structure of proteins, DNA, RNA and ATP – these are the primary source of N for heterotrophs i.e., they must consume those made by other organisms to use in their own DNA, RNA, ATP, etc… Some bacteria and algae use inorganic N sources. Some bacteria can fix N2. Regardless of how N enters the cell, it must be converted to NH3, the only form that can be combined with carbon to synthesize amino acids, etc. |
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Oxygen Sources
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Major component of carbohydrates, lipids, nucleic acids, and proteins.
Plays an important role in structural and enzymatic functions of cell. Component of inorganic salts (sulfates, phosphates, nitrates) and water O2 makes up 20% of atmosphere. Essential to metabolism of many organisms. |
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Hydrogen Sources
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Major element in all organic compounds and several inorganic ones (water, salts, and gases.)
Gases are produced and used by microbes. Roles of hydrogen: Maintaining pH Acceptor of oxygen during cell respiration. Gradient creation in cell respiration. |
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Phosphorous (Phosphate Sources)
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Main inorganic source is phosphate (PO4-3) derived from phosphoric acid (H3PO4) found in rocks and oceanic mineral deposits.
Key component of nucleic acids, essential to genetics. Serves in energy transfers (ATP) |
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Sulfur Sources
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Widely distributed in environment, rocks; sediments contain sulfate, sulfides, hydrogen sulfide gas and sulfur.
Essential component of some vitamins and the amino acids: methionine and cysteine. Contributes to stability of proteins by forming disulfide bonds. |
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Other Nutrients Important in Microbial Metabolism:
Potassium |
Essential to protein synthesis and membrane function.
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Other Nutrients Important in Microbial Metabolism:
Sodium |
Important to some types of cell transport.
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Other Nutrients Important in Microbial Metabolism:
Calcium |
Cell wall and endospore stabilizer.
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Other Nutrients Important in Microbial Metabolism:
Magnesium |
Component of chlorophyll; membrane and ribosome stabilizer.
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Other Nutrients Important in Microbial Metabolism:
Iron |
Component of proteins of cell respiration.
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Chemotroph
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Gain energy from chemical compounds.
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Phototrophs
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Gain energy through photosynthesis.
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Photoautotrophs
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Photosynthesis
Oxygenic photosynthesis Anoxygenic photosynthesis |
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Chemoautotrophs
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Survive totally on inorganic substances.
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Methanogens
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A kind of chemoautotroph, produce methane gas under anaerobic conditions.
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Heterotrophs and Their Energy Sources
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Majority are chemoheterotrophs.
Aerobic respiration. Two categories: Saprobes: free-living microorganisms that feed on organic detritus from dead organisms. Opportunistic pathogen. Facultative parasite. Parasites: derive nutrients from host. Pathogens Some are obligate parasites. |
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Passive transport
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Does not require energy; substances exist in a gradient and move from areas of higher concentration toward areas of lower concentration.
Diffusion Osmosis – diffusion of water. Facilitated diffusion – requires a carrier. |
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Active transport
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Requires energy and carrier proteins; gradient independent.
Active transport Group translocation – transported molecule chemically altered Bulk transport – endocytosis, exocytosis, pinocytosis. |
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Osmosis
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The movement of water across a selectively permeable membrane.
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Hypertonic solution
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Concentration is greater than the concentration inside the cell.
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Hypotonic solution
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Concentration is less than the concentration inside the cell.
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Isotonic solution
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Concentration is equal with the concentration inside the cell.
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Facilitated Diffusion
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1. Does not use energy (passive).
2. Uses a protein channel. 3. Protein changes shape to allow molecule inside or outside of cell. 4. Relies on a concentration gradient. |
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Carrier mediated active transport
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1. Requires energy (Active transport).
2. Runs independent of the concentration gradient. |
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Endocytosis
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Requires energy (active transport). Object is engulfed by cell membrane to be carried into the cell in a vesicle.
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Exocytosis
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Requires energy (active transport). Object is expelled from the membrane.
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Niche
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Totality of adaptations organisms make to their habitat.
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Environmental factors affect the function of metabolic enzymes:
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Temperature
Oxygen requirements pH Osmotic pressure Barometric pressure |
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Minimum temperature
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Lowest temperature that permits a microbe’s growth and metabolism.
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Maximum temperature
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Highest temperature that permits a microbe’s growth and metabolism.
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Optimum temperature
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Promotes the fastest rate of growth and metabolism.
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Psychrophiles
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Optimum temperature below 15C
Capable of growth at 0C |
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Mesophiles
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Optimum temperature 20-40C Most human pathogens
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Thermophiles
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Optimum temperature greater than 45C.
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Toxic Products of Oxygen
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1. Singlet oxygen (1O2)
2. Superoxide ion (O2-) 3. Peroxide (H2O2) 4. Hydroxyl radicals (OH-) |
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Enzymes that neutralize the toxic effects of oxygen:
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1. Superoxide dismutase
2. Catalase |
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Aerobe
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Utilizes oxygen and can detoxify it.
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Obligate aerobe
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Cannot grow without oxygen.
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Facultative anaerobe
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Utilizes oxygen but can also grow in its absence.
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Microaerophilic
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Requires only a small amount of oxygen.
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Anaerobe
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Does not utilize oxygen.
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Obligate anaerobe
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Lacks the enzymes to detoxify oxygen so cannot survive in an oxygen environment.
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Aerotolerant anaerobes
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Do not utilize oxygen but can survive and grow in its presence.
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Capnophile
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Grows best at higher CO2 tensions than normally present in the atmosphere.
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Majority of microorganisms grow at a pH between:
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6 and 8
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Obligate acidophiles
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Grow at extreme acid pH.
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Alkalinophiles
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Grow at extreme alkaline pH.
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Halophiles
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Require a high concentration of salt.
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Osmotolerant
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Do not require high concentration of solute but can tolerate it when it occurs.
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Symbiotic:
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Organisms live in close nutritional relationships; required by one or both members.
Mutualism Commensalism Parasitism |
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Non Symbiotic:
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Organisms are free-living; relationships not required for survival.
Synergism Antagonism |
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Mutualism
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Obligatory, dependent; both members benefit.
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Commensalism
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The commensal benefits; other member not harmed.
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Parasitism
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Parasite is dependent and benefits; host is harmed.
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Synergism
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Members cooperate and share nutrients.
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Antagonism
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Some members are inhibited or destroyed by others.
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Interrelationships Between Microbes and Humans
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Human body is a rich habitat for symbiotic bacteria, fungi, and a few protozoa - normal microbial flora.
Commensal, parasitic, and synergistic relationships |
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Microbial Biofilms
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1. Free swimming cells settle on a surface and remain there.
2. Cells synthesize a sticky matrix that holds them tightly to the substrate. 3. When biofilm grows to a certain density (quorum), the cells release inducer molecules that can coordinate a response. 4. Enlargement of one cell to show genetic induction. Inducer molecule stimulates expression of a particular gene and synthesis of a protein product, such as an enzyme. 5. Cells secrete their enzymes in unison to digest food particles. 6. Dominate the structure of most natural environments on earth. |
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Quorum Sensing
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Communicate and cooperate in the formation and function of biofilms.
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Binary Fission
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Parent cell enlarges, duplicates its chromosome, and forms a central transverse septum dividing the cell into two daughter cells.
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Generation, or Doubling Time
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Time required for a complete fission cycle.
Generation times vary from minutes to days. |
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Exponential Growth
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Each new fission cycle increases the population by a factor of 2.
Generation times vary from minutes to days. |
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Growth Curve
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Populations typically display a predictable growth pattern over time.
1. Lag Phase 2. Exponential Growth Phase 3. Stationary Phase 4. Death Phase |
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Lag phase
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“Flat” period of adjustment, enlargement; little growth.
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Exponential growth phase
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A period of maximum growth will continue as long as cells have adequate nutrients and a favorable environment.
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Stationary phase
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Rate of cell growth equals rate of cell death caused by depleted nutrients and O2, excretion of organic acids and pollutants.
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Death phase
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As limiting factors intensify, cells die exponentially.
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Methods of Analyzing Population Growth
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1. Turbidometry – most simple.
2. Degree of cloudiness, turbidity, reflects the relative population size. 3. Enumeration of bacteria: Viable colony count (AKA Viable Plate Count) Direct cell count – count all cells present; automated or manual. |
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Metabolism
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All chemical and physical workings of a cell.
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Catabolism
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Degradative; breaks the bonds of larger molecules forming smaller molecules; releases energy.
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Anabolism
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Biosynthesis; process that forms larger macromolecules from smaller molecules; requires energy input.
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Enzymes
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1. Biological catalysts that increase the rate of a chemical reaction by lowering the energy of activation.
2. The energy of activation is the resistance to a reaction. 3. The enzyme is not permanently altered in the reaction. 4. Enzyme promotes a reaction by serving as a physical site for specific substrate molecules to position. 5. Most composed of protein. |
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Enzyme Structure
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Simple enzymes – consist of protein alone.
Conjugated enzymes or holoenzymes – contain protein and nonprotein molecules. Apoenzyme – protein portion. Cofactors – nonprotein portion. Metallic cofactors: iron, copper, magnesium Coenzymes, organic molecules: vitamins. |
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Active Site, or Catalytic Site
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Site for substrate binding in an enzymatic reaction.
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Induced Fit
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A temporary enzyme-substrate union occurs when substrate moves into active site.
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Exoenzymes
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Transported extracellularly, where they break down large food molecules or harmful chemicals.
Cellulase, amylase, penicillinase. |
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Endoenzymes
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retained intracellularly and function there.
Most enzymes are endoenzymes. |
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Constitutive enzymes
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Always present, always produced in equal amounts or at equal rates, regardless of amount of substrate.
Enzymes involved in glucose metabolism. |
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Regulated enzymes
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Not constantly present. Production is turned on (induced) or turned off (repressed) in response to changes in concentration of the substrate.
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Synthesis or Condensation Reactions
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Anabolic reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond formed (AKA dehydration).
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Hydrolysis Reactions
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Catabolic reactions that break down substrates into small molecules; requires the input of water to break bonds.
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Sensitivity of Enzymes to Their Environment
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Activity of an enzyme is influenced by cell’s environment.
Enzymes operate under temperature, pH, and osmotic pressure of organism’s habitat. When enzymes are subjected to changes in organism’s habitat they become unstable. |
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Labile
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Chemically unstable enzymes.
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Denaturation
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Weak bonds that maintain the shape of the apoenzyme are broken.
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Competitive Inhibition
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Substance that resembles normal substrate competes with substrate for active site.
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Noncompetitive Inhibition
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Enzymes are regulated by the binding of molecules other than the substrate on the active site.
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Noncompetitive Inhibition: Enzyme Repression
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Inhibits at the genetic level by controlling synthesis of key enzymes (Blocks synthesis).
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Noncompetitive Inhibition:
Enzyme Induction |
Enzymes are made only when suitable substrates are present.
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Endergonic reactions
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Consume energy.
Energy+A+B+Enzyme = C |
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Exergonic reactions
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Release energy.
X+Y+Enzyme = Z+Energy |
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Cell Energetics
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Energy present in chemical bonds of nutrients are trapped by specialized enzyme systems as the bonds of the nutrients are broke.
Energy released is temporarily stored in high energy phosphate molecules. The energy of these molecules is used in endergonic cell reactions. |
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Redox reactions
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1. Always occur in pairs.
2. There is an electron donor and electron acceptor which constitute a redox pair. 3. Process salvages electrons and their energy. 4. Released energy can be captured to phosphorylate ADP or another compound. |
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Electron and Proton Carriers
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Repeatedly accept and release electrons and hydrogen to facilitate the transfer of redox energy.
Most carriers are coenzymes: 1. NAD 2. FAD 3.NADP 4.Coenzyme A 5. Compounds of the respiratory chain. |
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Adenosine Triphosphate: ATP
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1. Metabolic “currency”.
2. Three part molecule consisting of: -Adenine – a nitrogenous base -Ribose – a 5-carbon sugar -3 phosphate groups. 3. ATP utilization and replenishment is a constant cycle in active cells. 4. Removal of the terminal phosphate releases energy. |
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Substrate-Level Phosphorylation
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Transfer of phosphate group from a phosphorylated compound (substrate) directly to ADP to for ATP.
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Oxidative Phosphorylation
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Series of redox reactions occurring during respiratory pathway to for ATP.
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Photophosphorylation
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ATP is formed utilizing the energy of sunlight.
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Bioenergetics
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Study of the mechanisms of cellular energy release.
Includes catabolic and anabolic reactions. Primary catabolism of fuels (glucose) proceeds through a series of three coupled pathways: 1. Glycolysis 2. Kreb’s cycle 3. Respiratory chain, electron transport. |
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Aerobic Respiration
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Series or enzyme-catalyzed reactions in which electrons are transferred from fuel molecules (glucose) to oxygen as a final electron acceptor.
1. Glycolysis – glucose (6C) is oxidized and split into 2 molecules of pyruvic acid (3C), NADH is generated. 2. TCA – processes pyruvic acid and generates 3 CO2 molecules , NADH and FADH2 are generated. 3. Electron transport chain – accepts electrons from NADH and FADH; generates energy through sequential redox reactions called oxidative phosphorylation. |
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Anaerobic Respiration
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Functions like aerobic respiration except it utilizes oxygen containing ions, rather than free oxygen, as the final electron acceptor.
-Nitrate (NO3-) and nitrite (NO2). Most obligate anaerobes use the H+ generated during glycolysis and the Kreb’s cycle to reduce some compound other than O2. |
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Fermentation
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Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen.
Uses organic compounds as terminal electron acceptors. Yields a small amount of ATP. Production of ethyl alcohol by yeasts acting on glucose. Formation of acid, gas, and other products by the action of various bacteria on pyruvic acid. Pyruvic Acid is changed to lactic acid. |
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Electron Transport and Oxidative Phosphorylation
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Final processing of electrons and hydrogen and the major generator of ATP.
Chain of redox carriers that receive electrons from reduced carriers (NADH and FADH2). ETS shuttles electrons down the chain, energy is released and subsequently captured and used by ATP synthase complexes to produce ATP – Oxidative phosphorylation. |
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Chemiosmosis
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The movement of ions across a selectively-permiable membrane, down their electrochemical gradient. More spacifically for the release of ATP.
As the electron transport carriers shuttle electrons, they actively pump hydrogen ions (protons) across the membrane setting up a gradient of hydrogen ions – proton motive force. Hydrogen ions diffuse back through the ATP synthase complex causing it to rotate, causing a 3-dimensional change resulting in the production of ATP. |
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Terminal Step in Aerobic Respiration
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Oxygen accepts 2 electrons from the ETS and then picks up 2 hydrogen ions from the solution to form a molecule of water. Oxygen is the final electron acceptor
2H+ + 2e- + ½O2 → H2O |
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Amphibolic
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Many pathways of metabolism are bi-directional or amphibolic.
Catabolic pathways contain molecular intermediates (metabolites) that can be diverted into anabolic pathways. Pyruvic acid can be converted into amino acids through amination. Amino acids can be converted into energy sources through deamination. Glyceraldehyde-3-phosphate can be converted into precursors for amino acids, carbohydrates, and fats. |
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Photosynthesis:
Light-Dependent |
Photons are absorbed by chlorophyll, carotenoid, and phycobilin pigments.
Water split by photolysis, releasing O2 gas and provide electrons to drive photophosphorylation. Released light energy used to synthesize ATP and NADPH. |
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Photosynthesis:
Light-Independent Reaction |
Dark reactions.
Calvin cycle – uses ATP to fix CO2 to ribulose-1,5-bisphosphate and convert it to glucose. |
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Genetics
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the study of heredity
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Genome
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sum total of genetic material of a cell (chromosomes + mitochondria/chloroplasts and/or plasmids)
Genome of cells – DNA Genome of viruses – DNA or RNA |
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genes
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Chromosome is subdivided into genes, the fundamental unit of heredity responsible for a given trait
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genotype
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All types of genes constitute the genetic makeup
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phenotype
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The expression of the genotype creates observable traits
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DNA
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Two strands twisted into a double helix
Basic unit of DNA structure is a nucleotide Each nucleotide consists of 3 parts: A 5 carbon sugar – deoxyribose A phosphate group A nitrogenous base – adenine, guanine, thymine, cytosine Nucleotides covalently bond to form a sugar-phosphate linkage – the backbone Each sugar attaches to two phosphates – 5′ carbon and 3′ carbon |
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DNA Replication
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Making an exact duplicate of the DNA involves 30 different enzymes
Begins at an origin of replication Helicase unwinds and unzips the DNA double helix An RNA primer is synthesized at the origin of replication DNA polymerase III adds nucleotides in a 5′ to 3′ direction Leading strand – synthesized continuously in 5′ to 3′ direction Lagging strand – synthesized 5′ to 3′ in short segments; overall direction is 3′ to 5 |
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semiconservative
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DNA replication is semiconservative because each chromosome ends up with one new strand of DNA and one old strand
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transcription
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Information stored on the DNA molecule is conveyed to RNA molecules through the process of transcription
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translation
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The information contained in the RNA molecule is then used to produce proteins in the process of translation
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Gene-Protein Connection
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Each triplet of nucleotides on the RNA specifies a particular amino acid
A protein’s primary structure determines its shape and function Proteins determine phenotype. Living things are what their proteins make them. DNA is mainly a blueprint that tells the cell which kinds of proteins to make and how to make them |
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RNAs
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Single-stranded molecule made of nucleotides
5 carbon sugar is ribose 4 nitrogen bases – adenine, uracil, guanine, cytosine Phosphate |
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Messenger RNA (mRNA
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carries DNA message through complementary copy; message is in triplets called codons
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Transfer RNA (tRNA)
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made from DNA; secondary structure creates loops; bottom loop exposes a triplet of nucleotides called anticodon which designates specificity and complements mRNA; carries specific amino acids to ribosomes
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Ribosomal RNA –(rRNA)
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component of ribosomes where protein synthesis occurs
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how many Termination codons
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3
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Polyribosomal complex
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allows for the synthesis of many protein molecules simultaneously from the same mRNA molecule
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start codon
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AUG
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AUG
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formyl-methionine
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operons
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a set of genes, all of which are regulated as a single unit
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types of operons
Inducible |
operon is turned ON by substrate: catabolic operons - enzymes needed to metabolize a nutrient are produced when needed
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types of operons
–Repressible |
genes in a series are turned OFF by the product synthesized; anabolic operon –enzymes used to synthesize an amino acid stop being produced when they are not needed
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Lactose Operon
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Inducible Operon
Normally off Lactose turns the operon on |
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Regulator
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gene that codes for repressor
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Arginine Operon
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Repressible
Normally on and will be turned off when the product of the pathway is no longer required When excess arginine is present, it binds to the repressor and changes it. Then the repressor binds to the operator and blocks arginine synthesis. |
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mutation
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A change in phenotype due to a change in genotype
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wild type (wild strain)
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A natural, nonmutated characteristic
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mutant strain
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An organism that has a mutation
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Spontaneous mutations
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random change in the DNA due to errors in replication that occur without known cause
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Induced mutations
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result from exposure to known mutagens, physical (primarily radiation) or chemical agents that interact with DNA in a disruptive manner
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Point mutation
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addition, deletion, or substitution of a few bases
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Missense mutation
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causes change in a single amino acid
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Nonsense mutation
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changes a normal codon into a stop codon
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Silent mutation
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alters a base but does not change the amino acid
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Back-mutation –
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when a mutated gene reverses to its original base composition
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Frameshift mutation
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when the reading frame of the mRNA is altered
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The Ames Test
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Any chemical capable of mutating bacterial DNA can similarly mutate mammalian DNA
Agricultural, industrial, and medicinal compounds are screened using the Ames test |
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Genetic recombination
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occurs when an organism acquires and expresses genes that originated in another organism
3 means for genetic recombination in bacteria: Conjugation Transformation Transduction |
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Transformation
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chromosome fragments from a lysed cell are accepted by a recipient cell; the genetic code of the DNA fragment is acquired by the recipient
Donor and recipient cells can be unrelated Useful tool in recombinant DNA technology |
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Transduction
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bacteriophage serves as a carrier of DNA from a donor cell to a recipient cell
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Generalized transduction
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random fragments of disintegrating host DNA are picked up by the phage during assembly; any gene can be transmitted this way
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Specialized transduction
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a highly specific part of the host genome is regularly incorporated into the virus
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Transposons
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Special DNA segments that have the capability of moving from one location in the genome to another – “jumping genes
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Microbial Control methods:
Physical Agents |
Heat (Dry & Moist)
Radiation |
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Microbial Control methods:
Chemical Agents |
Gase
Liquids |
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Microbial Control methods:
Mechanical Removal Methods |
Filtration (Air & Liquids)
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Physical Agents
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Sterilization:
Incineration Dry Oven Steam Under Pressure Ionizing/X Ray, Cathode, Gamma Disinfection: Boiling/Hot Water/Pasteurization Nonionizing/UV |
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Chemical Agents:
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Sterilazition:
Gases Liquids Disinfection: Gases Liquids Antisepsis: Liquids |
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Mechanical Removal Methods
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Sterilization:
Filtration/Liquids Disinfection: Filtration/ Air |
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Disinfection
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The destruction or removal of vegatitive pathogens but not bacterial endospores. Usually used only on inanimate objects.
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Sterilization
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The complete removal or destruction of all viable microorganisims. Used on inanimate objects.
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Antisepsis
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Chemicals applied to body surfaces to destroy or inhibit vegetative pathogens.
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Relative Resistance of Microbes
Highest resistance |
Prions, bacterial endospores
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Relative Resistance of Microbes
Moderate resistance |
Pseudomonas sp.
Mycobacterium tuberculosis Staphylococcus aureus Protozoan cysts |
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Relative Resistance of Microbes
Least resistance |
Most bacterial vegetative cells
Fungal spores and hyphae, yeast Enveloped viruses Protozoan trophozoites |
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Sanitization
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any cleansing technique that mechanically removes microbes
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Degermation
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reduces the number of microbes through mechanical means
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Antimicrobial Agents’ Modes of Action
Cellular targets of physical and chemical agents |
The cell wall – cell wall becomes fragile and cell lyses; some antimicrobial drugs, detergents, and alcohol
The cell membrane – loses integrity; detergent surfactants Protein and nucleic acid synthesis – prevention of replication, transcription, translation, peptide bond formation, protein synthesis; chloramphenicol, ultraviolet radiation, formaldehyde Proteins – disrupt or denature proteins; alcohols, phenols, acids, heat |
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Thermal death time (TDT)
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shortest length of time required to kill all test microbes at a specified temperature
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Thermal death point (TDP)
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lowest temperature required to kill all microbes in a sample in 10 minutes
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Some desirable qualities of chemicals:
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Rapid action in low concentration
Solubility in water or alcohol, stable Broad spectrum, low toxicity Penetrating Noncorrosive and nonstaining Affordable and readily available |
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Levels of Chemical Decontamination
High-level germicides |
kill endospores; may be sterilants
Devices that are not heat sterilizable and intended to be used in sterile environments (body tissue) |
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Levels of Chemical Decontamination
Intermediate-level |
kill fungal spores (not endospores), tubercle bacillus, and viruses
Used to disinfect devices that will come in contact with mucous membranes but are not invasive |
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Levels of Chemical Decontamination
Low-level |
eliminate only vegetative bacteria, vegetative fungal cells, and some viruses
Clean surfaces that touch skin but not mucous membranes |
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selectively toxic
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drugs should kill or inhibit microbial cells without simultaneously damaging host tissues
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Mechanisms of Drug Action
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Inhibition of cell wall synthesis
Breakdown of cell membrane structure or function Inhibition of nucleic acid synthesis, structure or function Inhibition of protein synthesis Blocks on key metabolic pathways |
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Narrow-spectrum
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effective on a small range of microbes
Target a specific cell component that is found only in certain microbes |
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Broad-spectrum
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greatest range of activity
Target cell components common to most pathogens (ribosomes) |
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Competitive inhibition
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drug competes with normal substrate for enzyme’s active site
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Synergistic effect
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the effects of a combination of antibiotics are greater than the sum of the effects of the individual antibiotics
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Antibacterial Drugs that Act on the Cell Wall
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Beta-lactam antimicrobials - all contain a highly reactive 3 carbon, 1 nitrogen ring
Primary mode of action is to interfere with cell wall synthesis Greater than ½ of all antimicrobic drugs are beta-lactams Penicillins and cephalosporins most prominent beta-lactams |
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The Acquisition of Drug Resistance
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Adaptive response in which microorganisms begin to tolerate an amount of drug that would ordinarily be inhibitory; due to genetic versatility or variation; intrinsic and acquired
Acquired resistance: Spontaneous mutations in critical chromosomal genes Acquisition of new genes or sets of genes via transfer from another species Originates from resistance factors (plasmids) encoded with drug resistance, transposons |
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Mechanisms of Drug Resistance
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Drug inactivation by acquired enzymatic activity – penicillinases
Decreased permeability to drug or increased elimination of drug from cell – acquired or mutation Change in drug receptors – mutation or acquisition Change in metabolic patterns – mutation of original enzyme |
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Considerations in Selecting an Antimicrobial Drug
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Identify the microorganism causing the infection
Test the microorganism’s susceptibility (sensitivity) to various drugs in vitro when indicated The overall medical condition of the patient |
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Cephalosporins
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Account for one-third of all antibiotics administered
Synthetically altered beta-lactam structure Relatively broad-spectrum, resistant to most penicillinases, and cause fewer allergic reactions Some are given orally; many must be administered parenterally Generic names have root – cef, ceph, or kef |
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Cephalosporins
4 generations exist: each group more effective against gram-negatives than the one before with improved dosing schedule and fewer side effects |
First generation
Second generation Third generation Fourth generation |
