Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
71 Cards in this Set
- Front
- Back
|
What is a human Microbiome? |
A human microbiome: - a cataloguing of all the microbes in/on the human body. - Types, numbers, distribution etc. - learning the roles of microbes in health and disease. |
|
|
What is a cell without a true nucleus? |
A procaryote has no true nucleus and thus its genetic material is not enclosed in a membrane. |
|
|
What are cells with membrane-bound organelles (nucleus, etc)? |
Eucaryote. |
|
|
What organisms are within the 'three kingdom' system? |
1. eukarya (eucaryotic fungi, parasites, animals, etc.) 2. Bacteria (Eubacteria); includes all the common bacteria 3. Archaea (ancient bacteria). |
|
|
What's special about Archaea? |
Archaea (ancient bacteria), inhabit extreme environments (hot springs, freezing temps, ect.). - they are similar in appearance to bacteria, but differ in genetics, physiology, and biochemistry. |
|
|
Discuss the basic nomenclature and taxonomy of Bacteria. |
1. all bacteria can be categorized into related groups based on the number of characteristics they have in common. (metabolism, appearance, etc.) 2. basic unit of bacterial taxonomy is the 'strain'. 3. similar strains are grouped into species, then into genus, etc. |
|
|
True or false. Strains are identical to each other. Species differ by <5% Genus differ by <30% |
True. Strain: A groupof cells all descended from one parental cell (and thus all cells in the groupare identical to each other in all properties) Species → agroup of strains that differ from each other by < 5% Genus → a group of species that differ fromeach other by < 30% |
|
|
Why do we bother with bacterial taxonomy? |
1. as an aid to communication (there are 3500 different named bacteria). 2. As a way to assess the 'relatedness of different bacteria'. 3. In clinical practice, different bacteria may cause very similar or very different clinical conditions and respond differently to therapy. |
|
|
When we are observing bacteria using visible light and obtaining a view of up to 1000x magnification. What tool are we using? |
A light microscope. - it is sufficient for most routine purposes. - can see the shape, size, arrangement, and some structural features. |
|
|
Why would we use an electron microscope? |
The electron microscope uses electrons as a 'light' source to achieve magnification up to 200,000x. - we use to to see small structural details. - but it's not common for regular use (expensive, complex, takes time). |
|
|
How would you use a simple stain to observe bacteria under light microscope? |
Simple stain - single die (all bacteria appear as same colour, quick, but can't tell if more than one species present if same size and shape.) 1. spread thin layer of bacteria on glass and let dry (the smear). 2. "fix" the smear using gentle heating - this kills the bacteria and fixes them to the slide. 3. Stain the bacteria by flooding with dye. 4. observe in microscope. |
|
|
Why would you use a differential stain? |
A differential stain uses two (or more) dyes in combination. this allows the bacteria of the same size and shape to be differentiated based on cell surface structure. |
|
|
Describe the process of using a Gram stain. |
1. Spread thin layer of bacteria and let dry. 2. fix the smear- gentle heating 3. stain the bacteria by flooding with the stain 'crystal violet'. 4. Flood with Mordant iodine to fix the stain. 5. use alcohol or acetone to wash away stain that doesn't stick to cells. (counterstain) 6. use the die (safrinin) which will die the gram negative cells red. in the end; gram positive are purple gram negative red. |
|
|
What is special about the Gram stain? Why is it important? |
The Gram Stain: - infented by Hans Christian Gram. - most important differential stain (used in bacterial identification) - Divides bacteria into two broad groups; Gram positive (purple) and Gram negative (red) - it rapidly allows practitioners to determine if there are bacteria in a body site that normally should not contain bacteria. - therapy can be initiated quickly. |
|
|
When would you use an acid-fast stain. What's the process? |
Mycobacteria are acid-fast (most other bacteria are not). Used to help diagnose tuberculosis (Mycobacterium tuberculosis) Acid - Fast Stain 1. Applyred primary stain 2. De-colorize with acidic alcohol 3. Counterstain with blue stain “Acid-fast” bacteria will not de-colorize (retainprimary stain & stay red) Non acid-fast bacteria will de-colorize (lose primary stain & counterstain blue) |
|
|
Robert Hooke |
Robert Hooke (1660’s)· Developsconcept that all living things are made up of “cells”. · Microscopicobservation of larger microorganisms (fungi, parasites), |
|
|
Antonie van Leeuwenhoek (1676) |
Antonie van Leeuwenhoek (1676)· Usessimple microscopes to see “animalcules” (little animals) in naturalenvironments (pond water, tooth scrapings, etc.)· Firstobservation of smaller microorganisms (bacteria) |
|
|
Pasteur (1857) |
· Pasteur (1857) + others - suggests the “Germ Theory” ofdisease. If yeasts can cause physical/chemical changes infood, then maybe microorganisms can also cause physical changes in a human. ie. Thehypothesis that microorg. cause human diseases |
|
|
Robert Koch (1876) |
· Robert Koch (1876) Experimentallyproves the Germ Theory by developing a set of criteria that must befulfilled in order to show a direct cause-effect relationship between aspecific microbe and a specific disease |
|
|
Joseph Lister (1865) |
Joseph Lister (1865) Preventingmicrobes from entering surgical wounds (sterilizing of instruments, use of carbolic acid dressings)resulted in a decrease in post-surgical infections and mortality Establishing the principles & procedures for “Infection Control” |
|
|
· Florence Nightingale (1850’s) |
Florence Nightingale (1850’s) Promotedhospital cleanliness as a way to prevent infections “Wiseand humane management of the patient is the best safeguard against infection. The greater part of nursing consists ofpreserving cleanliness.” |
|
|
Edward Jenner (1796) |
Edward Jenner (1796) Peoplewho had come down with a cowpox infection never became infected with thesmallpox virus → Intentionally infecteda boy with cowpox virus and showed that the boy was then protected againstsmallpox = Beginnings of “vaccination” (vacca for cow). |
|
|
What is a pure culture? |
Pure culture ; A population consisting of only onespecies or strain, where every cell is genetically identical to every othercell. Can get one via the 'streak plating' method. |
|
|
Why do we want a pure culture of bacteria? |
Why do we want a pure culture of bacteria? Recall: Fulfilling Koch’s Postulates LaboratoryID of bacteria, determining antibiotic resistance, etc. can only be reliablyperformed if the culture is pure. |
|
|
What is the streak plating method? |
Streak Plating “Dilute” the mixed cell population by draggingthe bacteria over a solid growth media → Individual cells becomespatially separated and can grow into clearly-defined colonies after incubation |
|
|
Discuss the cell size and shape of a bacteria. |
Cell Size; Average 2 micron diameter (vs.8 micron red blood cell) Why size matters :Small sizeof bacteria = high surface-to-volume ratio o Nutrients/ wastes can efficiently move into / out of the cell, thus enabling very rapid cell growth · A large number of bacterial cells can occupy a small physical space o Enoughbacteria to start an infection (10 – 100 cells) can easily be introduced via avery small wound (eg. a needle poke) 2. Cell Shape & Arrangement · Bacillus(rod), Coccus (round), or Spirochete (spiral) arranged as singles, pairs,clusters, or chains. · Importantvisual characteristics used for the identification of medically relevantbacteria |
|
|
What is the function of cytoplasm? |
Cytoplasm ¨ - Gel-like internal matrix of the cell (mostly water) - ¨Location of the genetic material (DNA) in the form of Chromosome, Plasmids. etc. ¨Site of many cellular biochemical reactions - Biosynthetic enzymes - Nutrient storage sites - - Ribosomes (protein synthesis) |
|
|
Describe the significance of the cell envelope or cell 'wall' |
- Major structural component of bacterial cells- Determines gram staining reaction ® structurally different in gram neg. vs grampos. - Contains chemical subunits found nowhere else in nature- Target upon which some anti-microbial chemicals act - Interface between cell and its environment proteins which “sense” type of environment proteins required for pathogenicity (abilityto cause disease) |
|
|
What is the difference between gram negative and gram positive bacteria? |
Gram negative bacteria have; a. Plasma membrane b. Peptidoglycan (thin) c. Outer membrane. Gram positive Bacteria a. Plasma membrane b. peptidoglycan (thick) |
|
|
Describe the plasma membrane of a bacteria. |
Plasma membrane (a.k.a. “inner” or “cytoplasmic” membrane) 1. Phospholipid bi-layer + embedded proteins 2.Similar to the “cell membrane” of eucaryotic cells in general structure(but not function) 3. Functions:· - Permeability barrier; Prevents leakage of cytoplasmic content. - Location of some “metabolic” proteins - eg; Biosynthetic and energy-generating proteins - eg; Proteins which transport nutrients in, and wastes out |
|
|
What is Peptidoglycan? |
Peptidoglycan: - A structure only found in bacteria. - Consists of 'units' of two carbohydrates (N-acetylmuramicacid, N-acetylglucosamine) and four amino acids. - units linked together to create long chains. these chains are joined side by side to create a continuous mesh-like layer surrounding the cell. - this mesh can be built on top of one another to surround cell. (gram negative only a few layers, gram positive 70-80 layers). Peptidoglycan is a major structural element of bacteria; it give it strength and rigidity to the cell envelop. |
|
|
What does lysozyme do? |
Lysozyme - part of human's innate defence system against bacteria. Found in human secretatory fluids such as saliva, breast milk, tears, ect. - cleaves the bond between NAM and NAG in the peptidoglycan. (N-acetylmuramicacid, N-acetylglucosamine) |
|
|
Describe the outer membrane of a bacteria. |
Outer Membrane (Gram Neg bacteria only) ¨ Phospholipid bi-layer + embedded proteins ● Protein channels (“porins”) for entry of water and small molecules ● Binding / transport proteins (forentry of large nutrients ) ¨ Lipopolysaccharide (LPS) ● Found only in bacteria ● 3-part lipid + carbohydrate structure (partly buried in OM via lipid Agroup) ● Protective function ® helps repel toxic compounds in the environment ● Important in disease - O-antigen stimulates immune system - Lipid A causes fever, shock, inflammation\ LPS also known as Endotoxin |
|
|
What is the purpose of flagella and pili? |
Flagella; are filamentous structures capable of whip-like or propeller motions that provide motility. Pili; a short, thin, filaments covering entire cell. They are used for attachment of bacteria to other cells. Two types: sex pili (to other bacteria) and common pili (to eucharytoic cells.) ● Pili are important requirement for some bacteria to cause disease. |
|
|
What is the capsule of a bacteria? |
The Capsule or capsular polysaccharide, - is a viscou, sticky polysaccharide material that surrounds the cell. (making it look slimy/wet). - the chemical composition varies between strains. - provides protection; from chemicals, antibiotics, components of immune system, etc. and traps nutrients (protects from starvation). - Provides attachment; to host tissues and non-living surfaces. - "biofilms" |
|
|
What is a biofilm? |
Biofilm: ●A community of bacteria attached to a living or non-living surface viacapsular polysaccharide. ● Can be Single-species biofilms (mostlyin human infections) or Multi-species biofilms (mostlynatural environments). ●Biofilm formation prevents dislodging of bacteria and enables long-termpersistence in a particular environment |
|
|
How does a biofilm form? |
Formation of a biofilm is a complex,continuous process. 1. Initial attachment of single cells via capsular polysaccharide. 2. Cells multiply within the biofilm and form complex structures. 3. Release of free bacteria which can establish new biofilms elsewhere |
|
|
What is the significance of biofilms? |
Industrial; cause loss of billions $ per year in destruction of pipes such as water supply. Food contamination. Medical: 1. Bioflims form on humans during infections. eg; inner ear infections. an Estimated 60% of bacterial infections involve biofilms. 2. Biofilms form on implanted medical devices. 3. Difficult to remove with antibiotics (capsules, polysaccharide, block drug penetration.) 4. secondary biofilms/infections start elsewhere after release of free bacteria. |
|
|
Discuss endospores. |
Bacterial Spores (aka. Endospores) ● Conversion of a bacterial cell (mainly Gram positives) from a “vegetative”(growing) form into a dormant, non-growing form (“spore”) ●Triggered by an environmental stress (eg. lack of nutrients, etc.). - Cell’s DNA becomes encased in thick coat of modified peptidoglycan. - Rest of cell breaks down leaving intact spore. - Modified PG allows spore to be highly resistant to heat, chemicaldisinfectants, etc. ● Removal of stress allows spore to “germinate” and revert to the vegetative(growing) form ie. A survival Significance; ● pores are not killed bypasteurization, boiling, some germicides ● Important in some food - borne diseases ● Many bacteria in natural environments (eg.soil) produce spores |
|
|
Discuss C-difficile. |
Clostridium difficile ● is a gram positive, spore-forming anaerobicbacillus that may be present as part of the normal intestinal flora or acquiredthrough contact with health care facilities. ● Theenvironment can be an important indirect source of the organism especiallygiven that the spores can live in the environment for months. ● Assumption:ingestion of spores is the most common mode of transmission and contaminatedhands are assumed to be the main vector. ● Hand transmission of the organism can occur after contact with thepatient or the contaminated environment mainly on the hands and gloves ofhealth care workers. Care: ● Gloves and Hand Cleansing ● Washhands with soap and water after the removal of gloves. Note: None of the antiseptic agentsused in hand rubs or soaps are reliably sporicidal against C.difficile. The physical action ofwashing and rinsing hands removes the spores. |
|
|
In what forms does genetic material exist in Bacteria? |
Two forms: Chromosomes and Plasmids. Chromosome: ●Circular double-stranded DNA molecule (vs Linearin eucaryotes). ●On per cell (vs >1 in most eucaryotes) ● Average of 3000-4000 genes (vs roughly 23,000 ina human) ● Highly folded (supercoiled) conformation so asto fit in the cell.· Plasmids: ●Circular, supercoiled, but separate from thechromosome. ●Smaller (5-100 genes), but usually >1 copyper cell. ●Genes on plasmids are usually not required forviability, but make the bacteria better adapted to their environment(“accessory” genes) Eg: metabolic genes (breakdown of unusualnutrients)· ●Genes needed to cause disease (“virulence”Genes)· ●Antibiotic resistance genes. |
|
|
What are the mechanisms in which bacteria achieve genetic diversity? |
1. Mutation. 2. Gene Transfer; (Transformation, transduction, and conjugation). |
|
|
Describe mutation. |
Mutation; a physical change in DNA sequence,which gives rise to a change in mRNA, and thus a change in the protein. Mutations can be either: ●Spontaneous; random errors introduced during DNAreplication. ●Induced: external agents (chemicals, radiation,etc.) which distort the physical structure of DNA and cause replicating enzymesto introduce an incorrect base. · In general, achieving genetic diversity viarandom mutation is a slow process – need lots of mutations to occur beforesignificant changes are seen. |
|
|
Describe Gene transfer. |
GeneticDiversity through gene transfer· Mechanisms which allow the exchange of largeblocks of genetic information (entire genes) between bacterial cells. (A morerapid way to create genetic diversity vs. mutation).· Three ways by which bacteria can ‘swap’ genes. 1. Transformation. 2. Transduction 3. Conjugation |
|
|
Describe Transformation. |
Transformation: ●Dead bacteria break open and spill fragments ofDNA into the environment. ● DNA fragments are taken up by other bacteria inthe environment. ●DNA fragments become incorporated into thebacteria’s chromosome. |
|
|
Describe Transduction. |
Transduction: ●DNA transfer via Bacteriophage (“Phage”) =Bacterial Virus. - Creation of a ‘transducing phage” – a phage thathas mistakenly been packaged with bacterial DNA àcan go on to inject this DNA into other bacterial cells. 1. Phage injects its DNA. 2. Phage enzymes degrade host DNA. 3. Cell synthesizes new phages that incorporatephage, DNA and, mistakenly, some host DNA. 4. Transducing phage injects donor DNA. 5. Donor DNA is incorporated into recipientchromosome by recombination. |
|
|
Describe conjugation. |
Conjugation (aka. “bacterial mating”)o ● Transfer of plasmids by direct cell-to-cellcontact. 1. Bacterial cell with a plasmid attaches to onewithout a plasmid via ‘sex pili’. 2. Two bacteria are drawn together, their envelopesfuse, and a small opening is created between then. 3. The plasmid replicates itself. One copy ispassed to the attached cell; the remaining copy is left behind. 4. Cells separate – both now carry the plasmid(note that the cell that was originally without a plasmid now carries newgenetic information.) Note: once a cell has acquired a plasmid, it canre-transfer it to other cells in a population àeventually all cells will have it.
Significance: - Probably a common event in nature; manydifferent species of bacteria carry plasmids. - A mechanism for spreading genes that havemedical significance (eg. Genes that aid ‘pathogenicity’, genes that giveantibiotic resistance). |
|
|
How do Bacteria 'grow'? |
Bacteria reproduce by 'Binary Fission'. ● one cell divides to create two identical daughter cells. ● time required for one binary fission event is called the generation time (G). ● (G) is species dependent and environment dependent. ● A population of bacteria will increase in an exponential manner over time. 1-2-4-8...etc. ● significance; Need for prompt intervention due to rapid 'growth'. But, in labs- the rapid growth makes it possible to identify disease-causing organism while there is time for proper treatment. ● the rapid growth allows us to measure cell numbers. |
|
|
How do we measure bacterial cell numbers? |
Measuring bacterial cell numbers. ● Quantitate the number of bacteria in a liquidsuspension by placing a known volume onto a solid nutritional support andcounting colonies; ● One colony (or CFU – colony forming unit) = onebacterial cell in original suspension. ● E.g. quantitation of bacteria in urine to diagnoseUTI’s. |
|
|
What are the nutrient requirements for bacteria? |
Nutrients (sources of Carbone and Minerals): ● Most bacteria (including all human pathogens) obtainall required nutrients and generate energy from the breakdown of organicmaterials (sugars, fats, proteins). ● Nutrient requirements range from the simple tothe complex. |
|
|
What are the water requirements for bacteria? |
Water: ● The “solvent” in which bio-molecules aredissolved and therefore an absolute necessity for growth (bacterial cells areroughly 80% water). ● spore formation allows for survival in dryconditions). ●Measured as “water activity” (Aw) = the amountof ‘free’ (unbound) water in a substance and presenceof dissolved solutes (salt, sugar, etc.) reduces the amount of free wateravailable (ie. Decrease Aw). ● Most bacterial species can only grow at Aw of0.85 – 0.99§ Aw is a critical parameter in food microbiology. ● ‘preserve’ foods by lowering Aw. Create a high sugar or salt environment. Desiccation. ●Defines what species will or will not grow in agiven food. ●Fungi are able to grow at lower Aw than bacteriaand are therefore more likely to cause food spoilage. |
|
|
What are the pH requirements for bacteria? |
pH (Acid/Alkali): ●Optimal for most species is neutrality ( roughlypH 7.0), although some tolerate sub-optimal conditions (generally not humanpathogens). Eg; acidophiles àpH 2.0-5.0· Eg; alkaliphiles à>9.0§ An extreme example; thiamonas thermosulfatus. ●Found in caves with high [sulfur]. ●Metabolizes sulfur to produce sulfuric acid aswaste product àsurvives in pH of 0.1 – 1 ● Grow as biofilms suspended from cave ceiling oras dense microbial mats on walls, floors. |
|
|
What are the temperature requirements for bacteria?
|
Temperature Requirements. ● Bacterial growth occurs over a temperaturerange, but best growth only occurs at one temperature (+ optimum temperature). ● Growth slows outside of optimum and stopsoutside min/max range. ● Note; temperature ranges and optimum temperaturevary greatly between different species of bacteria. Classifying bacteria based on growthtemperature: ● Psychrophiles: optimum temp 10°C. Food spoilage. ●Mesophiles: Optimum Temp 37°C. Majority ofbacterial species. ● Thermophiles: Optimum temperature 70°C. compost,hot springs, etc. Significance of Growth Temperature. ● In food preservation: Most pathogens (mesophiles) do not grow at<20°C. Refrigeration temp (5°C.) will: Prevent growth of disease-causing microbes and Slow the growth of spoilage microbes. ●In disease: - One reason why bacteria infect certain bodysites but not others. - As a form of therapy for bacterial infections(pre-antibiotic era). - Ex. Syphilis (treponema) optimum temp 30°C. Induce fever in patient so as to raise bodytemperature. |
|
|
What are the gaseous atmosphere requirements for bacteria? |
Gaseous Atmosphere Requirements (O2concentration). ● Bacteria can be categorized based on O2requirements. a. Aerobes (aka ‘obligate’ aerobes); absoluterequirement for oxygen in order to grow. b. Anaerbes (aka “Obligate’ anaerobes); rapidlykilled in the present of oxygen. - Metabolize oxygen into toxic by-products.Therefore can only survive in a completely O2-free environment. c. Facultative anaerobes: grow best if O2 present,but can also grow without it. · Significance of Oxygen Requirements: ● In disease: Another reason why some bacteria inhabit (andsometimes cause infections in) certain body sites but not others. ● In Lab Diagnostic procedures that involvegrowth: Anaerobes require special handling/growthconditions that include complete exclusion of oxygen. Forthe diagnosis of blood stream infections, a sample of blood is collected andplaced into two “Blood Culture Bottles” – one is an “aerobic bottle” designedto grow aerobic bacteria, and the other is an “anaerobic bottle” for anaerobegrowth. The instructions say that ifcollecting with a butterfly needle and tubing, you must fill the aerobicbottle first, and the anaerobic bottle last. |
|
|
What is differential media? |
There are no inhibitors added in differential media, all species can grow. - the bacteria are differentated between species based on appearance on media. eg; blood agar. |
|
|
What are the general characteristics of antibiotics? |
General Characteristics of Antibiotics: 1. Selective toxicity: ● Must kill bacteria w/o harming host. ● Expressed as therapeutic index (T.I.) = dosewhich is toxic to host/ dose required to kill bacteria § (higher is better). 2. Cidalvs static effect ●Bactericidal; kills bacteria. ●Bacteriostatic: only inhibits growth (growthresumes if the antibiotic is removed). 3. Spectrumof Activity ●Narrow spectrum àactive only against a few species. ●Broad spectrum àactive against many different species. ●But no antibiotic is universally effectiveagainst all species of bacteria. |
|
|
How do Antibiotics work? |
1. Block DNA or RNA synthesis. 2. block protein synthesis 3. inhibition of metabolic pathways. 4. disrupt bacterial cell membranes 5. block peptidoglycan synthesis |
|
|
Describe the MOA of Quinolones. |
Quinolones: ● Block DNA/RNA synthesis ●Inactivates DNA gyrase (enxyme which causes‘supercoiling’ of bacterial chromosome. ●No supercoiling àno DNA replication. |
|
|
Describe the MOA of Rifampin. |
Rifampin ● Block DNA/RNA synthesis. ●Binds to RNA polymerase à blocks messenger RNAsynthesis. |
|
|
Describe the MOA of Sulfonamide. |
Sulfonamide (and other ‘sulfa’ drugs) ● Creams/ointments ● Inhibit metabolic pathways. ● Blocks the synthesis of bacterial folic acid(and therefore DNA and RNA by acting as a ‘competitive inhibitor’ of the folicacid pathway. ● Similar in structure to PABA (para-amino-benzoicacid) the starting point for folic acid biosynthesis – sulfa enters into thefolic acid pathway in place of PABA, but cannot go on to make folic acid. ● polymyxin B: binds to phospholipids and becomesphysically inserted into membrane. ● Result: loss of membrane function. Dirsruptionof membrane integrity (leakage of ions, etc.) ● But: poor selective toxicity (prokaryote andeukaryotic membranes are similar); usually for external use only. (creams andointments). |
|
|
Describe the MOA of polymyxin B |
polymyxin B: ● creams/ointments ● Disrupt the bacterial cell membranes ● binds to phospholipids and becomesphysically inserted into membrane. ● Result: loss of membrane function. Dirsruptionof membrane integrity (leakage of ions, etc.) ● But: poor selective toxicity (prokaryote andeukaryotic membranes are similar); usually for external use only. (creams andointments). |
|
|
Describe the MOA of Beta-lactams (penicillins, cephalosporins) |
β-lactams ●penicillin, cephalosporins, etc. ● Block peptidoglycan synthesis ● Interferes with enzymes required for PGsynthesis. ●Final assembly of PG does not occur. ● Lysis of bacteria due to incomplete cell walls(bactericidal effect). |
|
|
What are adverse reactions associated with antibiotic use. |
1. toxicity to host; after high-dose, long term use. 2. allergic reactions 3. disruption of normal flora. - leading to superinfections. eg; Clostridium difficile ● Present in very low numbers of about 3% ofadults but kept in check by normal flora. ● Often resistant to multiple antibiotics.· Broad spectrum antibiotic use = excessive growthof C. Difficile ● Produces toxin àdamages gut cells and may perforate intestine (can lead to death). |
|
|
What are factors that influence which antibiotic to use? |
1. Patient-specific factors ● immune status. ● patient compliance. 2. Pharmacological factors; ● the antibiotic must get to site of infection, stay long enough at high enough concentrations to have antibacterial affect. ● must consider the absorption, distribution, metabolism and excretion. 3. Microbiological factors; ● confirm infection is bacterial. ● identify species. ● ensure bacteria are sensitive to antibiotic. ● antibiograms. |
|
|
What is an antibiogram? |
Antibiograms: a periodic summary oflocal/regional bacterial isolates and their antibiotic susceptibility patters. Useful as an aid for selecting appropriatetherapy. |
|
|
How do we measure resistance to antibiotics? |
1. Disk-Diffusion Method a. Spread test bacteria onto solid media. b. Add filter disk containing known concentrationof antibiotic. - Antibiotic diffuses into media. - Createsconcentration gradient. c. Allow bacteria to grow 18-24 hrs. d. Measure the area of growth inhibitionsurrounding the disk. 2. Tube-Dilution Method: a. Dilute antibiotic in a liquid media (high to lowconcentration) b. Add bacteria to the media containing dilutionsof antibiotic. c. Monitor for presence/absence of growth in themedia. ●Determines the “minimum inhibitionconcentration” (MIC) of the antibiotic. · ● The lowest concentration of antibiotic that willprevent bacterial growth. ● Tube dilution method provides more quantitativeinformation vs disk diffusion. ● Useful for proper dosing (aim for a body fluidconcentration of antibiotic that is 3-5x higher than the MIC) |
|
|
What are biochemical mechanisms of of Antibiotic Resistance? |
1. Direct breakdown of antibiotic by bacterial enzymes eg; beta-lactam ring of penicillin. 2. Promote excretion or prevention of uptake of an antibiotic. 3. alter (or bypass) the target of the antibiotic. |
|
|
How do bacteria become resistant? |
1. Spontaneous Mutation in DNA (eg; to give altereddrug target). ● Low frequency events, but presence of drug inenvironment exerts selective pressure so that the mutant cells persist.·
2. Obtain new resistance genes: (eg; gene forinactivating enzyme) ●Often found on plasmids (sometimes >1resistance gene on a single plasmid). |
|
|
What is selective Pressure? |
Selective Pressure:· ● Continuous exposure of bacteria to an antibioticcreates a strong selective pressure to develop resistance.· Comes from: ● Clinical overuse of antibiotics. Given before lab results are available or innapropriately for viral infection. ● Increased prophylactic use for at-risk patientsto prevent (vs to treat) infections (before/after surgery, etc.) ● Available OTC in many places w/o medicalsupervision. ●Patient non-compliance (failure to take drug asprescribed). ● Widespread use of antibiotics outside of humanhealth. (pets/agriculture) Creates natural reservoir of resistant bacteriain animals. Possible transfer of resistance genes to humanpathogens |
|
|
What are recommendations to reduce this Selective Pressure? |
●Restrict the use of some antibiotics in humanand animal health. ● Rotate the use of different types ofantibiotics. ● Use combination antibiotics to slow developmentof resistance. ●Promote responsible clinical use of antibioticsto HCWs. ●Better public education to limit un-necessaryantibiotic use. |
|
|
What are methods in finding new sources of antibiotics? |
1. Continue screening of new bacteria and fungi from environment. 2. Rejuvenate existing antibiotics (chemical modifications) 3. Novel non-microbial sources; eg plants. 4. Rational drug design "molecular pharmacology" - expensive, time consuming and no guarantees will work |
