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236 Cards in this Set
- Front
- Back
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What is symbiosis?
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living together
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What are symbionts?
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organisms which live together in a particular environment?
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What is commensalism?
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The microorganism benefits from the association whereas the host is neither benefited nor harmed
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What is mutualism
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a state in which both the host and the microorganism derive benefit
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What is parasitism
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a state in which the microorganism benefits at the expense of the host; the host may suffer or has severe disadvantages
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What is the first step of biochemical testing?
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obtaining a pure culture
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What must you do to a species in a clinical and other real life situations?
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isolate it
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What is the second step of biochemical testing?
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gram stain
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What information does the gram stain give?
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gram reaction, cell shape, and cell arrangement
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After the gram stain, what do you perform various tests for?
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to determine the cultural and biochemical characteristics of the organism
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If you were performing an isolation from a clinical standpoint, what might you also determine about the organism?
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sensitivity to various antibiotics
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What is the next step after performing a gram stain
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to determine the oxygen requirement of the organism, the catalase test, the oxidase test, and to detect for the presence of endospores
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Why would one consult bergey's manual?
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to determine which biochemical tests are necessary for further identification
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Why do you use double-strength TSB?
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broth that contains twice the density of nutrients in order to get cells in the log phase of growth
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What do gram positive bacteria look like in the log phase and why?
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gram negative bacteria because cell walls begin to break down if there are not enough nutrients left after log phase
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What is the characteristic of cells in the stationary phase?
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nutrients are almost exhausted, so tehy may not have been able to build complete cell walls, due to the lack of nutrients from the environment, thus theycannot retain the crystal violet sufficiently --> therefore results of Gram stain are inconclusive
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What are the four phases of bacterial growth?
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Lag, log (exponential), stationary, death
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What occurs in the lag phase?
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a period of very little or no cell division; not dormant cells that undergo a period of intense metabolic activity, such as the synthesis of enzymes to adjust to new growth conditions
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What occurs in the log phase?
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the time when cells are most metabolically active and products need to be produced very efficiently
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What occurs in the stationary phase?
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the period that the growth rate slows down, and much metabolic changes also occur here; the number of microbial death balances the number of new cells, and the population stabilizes
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What is the death phase?
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the period in which the number of deaths eventually exceeds the number of cells formed
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What can bacterium of the genus rhizobium reduce atmospheric nitrogen gas to?
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ammonia
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What is rhizobium?
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a symbiotic organism that invades the root hairs of legumes and forms nodules in the roots
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What can azotobacter and cyanobacteria do?
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fix nitrogen that are free-living in the soil
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What are clostridium?
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anaerobic nitrogen fixers
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Why are nitrogen-fixing bacteria valuable to agriculture?
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they enrich the soils with the forms of nitrogen that are then made available to plants for their utiliziation
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In a symbiotic relationship with the plant, what do both partner's do?
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benefit from each other's presense
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How does the plant benefit from bacteria in a symbioitic relationship?
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utilizes the nitrogen fixed in root nodules by the bacteria for growth of plant parts
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How do bacteria benefit from plants in a symbiotic relationship?
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bacteria obtain energy from carbohydrates synthesized the the plant
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What can neither legume nor rhizobium alone do under normal conditions?
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fix nitrogen
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What is nitrogen fixation?
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conversion of atmospheric nitrogen into usable compounds
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examples of plants able to undergo nitrogen fixation
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leguminous- pea, bean, soybean, alfalfa, clover
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examples of bacteria able to undergo nitrogen fixation
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genera rhizobium and bradyrhizobium (gram-negative rods)
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What is rhizobium
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gram negative bacteria that reduce nitrogen to ammonia
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What can plants not do?
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use atmospheric nitrogen gas
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What are the 2 enzymes involved in nitrogen fixation?
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nitrogenase and transaminase
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What do plants need nitrogen from the soil to make?
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amino acids and proteins
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What are the end products of nitrogen fixation?
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amino acids and proteins
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What kinds of organisms are staphylococci?
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saprophytes and parasites of the skin and mucus membranes
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In what part of the body are staphylococci normally located?
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nasopharynx, the uppermost part of the pharynx or throat that is continuous with the nasal passages
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How do staphylococci test in a catalase test?
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positive
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How are staphylococcus arranged under a microscope?
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Gram + cocci arranged in irregular clusters that resemble bunches of grapes
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How big are staphylococci colonies?
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medium sized
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What color are staphylococci colonies?
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off-white to golden
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What are the 2 major groups of staphylococci?
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Pathogenic and non-pathogenic
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What composes the pathogenic group of staphylococci?
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staph aureus strains
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What test is done to distinguish between pathogenic and non-pathogenic staphylococci?
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coagulase test or mannitol test
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What is the coagulase test?
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it is based on teh ability of pathogenic staphylococci to produce the enzyme coagulase which clots blood plasma without involving thrombin
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What is thrombin?
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a coagulation protein in the blood stream that has many effects in the coagulation cascade
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How does pathogenic staphylococci test in the coagulase test?
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positive
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How does non-pathogenic staphylococci test in the coagulase test?
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negative
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What is an example of non-pathogenic staphylococci?
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staph epidermidis, staph saprophycticus
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What are some infections caused by staph aureus?
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Wound infections, pneumonia, TSS, food poisoning
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What are infections caused by staph epidermidis?
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hospital acquired infections
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What are infections caused by staph saprophyticus?
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urinary tract infections
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How does streptococci test in a catalase test?
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negative
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What does streptococci look like under a microscope?
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gram positive cocci in pairs or chains
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What classification are streptococci?
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facultative anaerobes
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What are streptococci not tolerant to?
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high concentrations of NaCl, except group D
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What do streptococci ferment in general?
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lactose
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What do streptococci colonies appear as?
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small, white, drop=like, mucoid, unpigmented colonies
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How are streptococci most fastidious?
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require more nutrients to grow on and grow on limited number of media
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What are streptococci divided into 3 groups based on?
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hemolytic reaction on blood agar
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What are hemolysins?
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extracellular enzymes that can be detected by their ability to lyse/destroy red blood cells
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What are hemolysins produced by?
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pathogenic bacteria
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Where may hemolysins plaay a role in pathogenic bacteria?
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in their virulence, because they facilitate the escape of one of the host's protective mechanisms, like localization of the infecting organism by blood clot formation
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What happens when hemolysins lyse cells other than blood cells?
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they facilitate the spread of a pathogen from a tissue and allow pathogenic organisms to use nutrients released from lysed human cells
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What do alpha hemolysins do?
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partially lyse the red blood cells and reduce the hemoglobin (red pigment) to methemoglobin (greenish pigment)
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What are infections caused by streptococci?
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strep throat, scarlet fever, meningitis, pneumonia
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What is lancefield antigen typing?
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method of serological identification of beta-hemolytic stretococci
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Where are the antigens that are used in lancefield antigen typing located?
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on the cell wall of streptococci
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What does the use of monoclonal antibodies make it possible to detect?
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the presence of any beta-hemolytic streptococci group
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Can staph also produce hemolysis on blood agar?
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yes
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What is another method of grouping streptococci based on?
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serological properties
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What is an example of group A streptococci?
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S. pyogenes, which causes strep throat, is beta hemolytic, and is sensitive to Bacitracin
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What is an example of group B strep?
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S. agalactiae, which causes impetigo, acute endocarditis, and neonatal meningitis, is beta hemolytic; positive CAMP
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What is an example of group C streptococci?
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S. equi; much less serious infections, beta hemolytic, and sensitive to SXT
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What is an example of Group D?
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Enterrococci; positive bile esculin test, and tolerant to 6.5% NaCl; beta hemolytic; subacute endocarditis, meningitis, UTI
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What are the characteristics of streptococci Viridians?
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alpha hemolytic, opportunists that can cause serious illnesses in compromised individuals; SXT sensitive
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What are the characteristics of streptococci Pneumococci?
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strep penumoniae, alpha hemolytic; most frequent cause of bacterial pneumonia and is also responsible for many other diseases; differentiated by bile solubility test; optochin sensitive
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What test is used to differentiate between staph and strep?
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Catalase test
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What does catalase decompose hydrogen peroxide into?
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Water and oxygen
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What is the cell arrangement of staph?
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clusters
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What is the cell arrangement of strep?
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chains or pairs
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What are cocci in chains of strep formed by?
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repeated division in the same plane, and clusters by division in random planes
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What is mannitol salt agar (MSA)?
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a pink enrichment media for Staph that selects staph for its high salt concentration, which strep cannot tolerate
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What pH indicator does MSA contain?
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it is red and it turns medium/agar from pink to yellow (neutral to acidic) when mannitol is fermented
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What is the coagulase?
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an enzyme that converts fibrinogen into fibrin, forming a clot
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Where can the coagulase test be performed in?
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a slide or a tube
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How is the coagulase test done?
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bacteria are added to plasma and if a clot is formed, then coagulase is present and your Staph is in the pathogenic group
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What are the controls used in the coagulase test?
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S. aureus for coagulase positive, and S. epidermidis for coagulase negative
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What happens since the MSA test and coagulase test are correlated?
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if one has a positive result, as will the other
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What does the mannitol fermentation test differentiate between?
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mannitol fermenters and non fermenters
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What do fermenters produce?
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acid, thus changing the agar color from pink to yellow
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What does the novobiocin sensitivity test differentiate between?
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non-severe pathogenic staph species; S. epidermidis (sensitive) and S. saprophiticus (resistant)
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What does a zone of inhibition indicate in novobiocin test?
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sensitive
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What does no zone of inhibition indicate in a novobiocin test?
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resistant
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What are the biochemical tests for strep unknowns?
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hemolytic, bile solubility, antibiotic susceptibility, CAMP, bile esculin, and NaCl
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How is a hemolytic test done?
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examine the blood agar plates and determine the type of hemolysis; alpha- brownish greenish color; beta-clear opaque, transparent; gamma- red and opaque
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How is a bile solubility test done?
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plate is incubated for half an hour; bile salts have the ability to selectively lyse strep pneumoniae; gamma-hemolytic streptococci will remain intact and no lysis is observed
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What is the CAMP test used to identify?
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group B strep
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What does group B strep secrete?
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camp factor which enhances the hemolytic activity of Staph aureus
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How are the antibioitic susceptibility tests performed?
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to distinguish group A strep from other groups, antibiotic discs are place don a lawn of test bacteria.
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What does a zone of inhibition show in an antibiotic susceptibility test?
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that bacteria were sensitive to that particular antibiotic; and no zone of inhibition means no sensitive
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What can be detected using the CAMP test?
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group b, beta hemolytic stretococci
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What do group B strep secrete?
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a camp factor that enhances hemolytic activity of staphylococcus aureas beta lysins for rbs
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what happens when group b strep and staphylococcus overlap on a blood agar plate?
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accentuation of the beta hemolytic reaction occurs
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What is the positive control in a CAMP test?
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stre. agalactiae
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What does a positive camp test show?
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a triangular zone of enhanced clearning by s. aureus
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What does the bile esculin test identify?
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group d strep
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What can group d strep hydrolyze bile-esculin into?
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esculetin and glucose
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What can esculetin be visualized by?
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adding ferric citrate, which will form a black-gray complex, indicating a positive result
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What is the NaCl tolerance test done to?
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differentiate between group d strep
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What does a positive result of NaCl show?
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turbidity in 6.5% NaCl broth
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What may the meduium in an NaCl test change color from?
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deep purple to light purple--> positive result
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When can normal flora produce diseases?
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When the host immune system is suppressed
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What is an opportunistic infection?
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a kind of pathogenic infection that usually does not cause disease in a healthy host, but does in a compromised immune system
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What organisms does the large intestine contain?
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gram-negative, obligate-anaerboic rods, mainly bateriodes and fusobacterium species
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What is the intestinal tract of healthy individuals home to?
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Enterobacteriaceae, the aerobic genera Alcaligenes and Pseudomonas, and a number of Gram-positive genera, and families of Vibrionaceae and Spirillaceae
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How many genera does enterobacteriaceae include?
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twelve genera
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What are the gram-positive genera that are in the intestinal tract?
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Clostridium, lactobacillus, streptococcus, and bacillus
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What flora are enterics a part of?
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normal flora; some are pathogenic
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What is the size of enterics?
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Small in size
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What kind of rods are enterics?
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gram negative
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What kind of anaerobes are enterics?
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facultative
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How do enterics test in an oxidase test?
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Negative
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How do enterics test in a catalase test?
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positive
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How are enterics characterized in terms of spores?
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non-spore forming
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How are enterics characterized in terms of glucose?
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all ferment glucose
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What genera do the most important enteric pathogens belong to?
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general Salmonella and Shigella
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What do some Salmonella species cause?
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enteric fevers like typhoid fever
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What do some shigella species cause?
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Dysentry
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What is edwardsiella tarda?
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acute gastroenteritis
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What is yersinia spp associated with?
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enterocolitis and plague
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What bacteria causes enterocolitis?
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enterocolitica
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What bacteria causes plague?
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Y. pestis
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Where else is enterobacter found besides the human body?
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in nautre, in fresh water, soil, sewage, and plants
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What does vibrio cholerae cause?
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cholera
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How id vibrio cholerae distinguished from the enterics?
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by its curved rods and positive oxidase test
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What bacteria are commonly found in urinary tract infections but not in GI tract infections?
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Genus hafnia, genus morganella, genus providencia
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Which genera are opportunistic pathogens?
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Erwinia and Edwardsiella
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Which pathogenic enteric causes urinary tract infection?
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proteus spp
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What do E. Coli cause?
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infant diarrhea and Monetezuma's revenge
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What is a coliform?
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a gramnegative, non-spore forming, falcultatively anaerobic rod, which can ferment lactose
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What do non-coliform enterics include?
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Salmonella, Shigella, Proteus and Yersinia
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What can non-coliform enterics not ferment?
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lactose
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What color colonies do coliforms produce?
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red
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What kind of colonies do non-coliforms produce?
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colorless
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What kind of enterics are non-coliform?
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pathogenic
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What tests are used for rapid identification of enterobacteriaceae?
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IMVIC, and sugar fermentation pattern on Triple Sugar Iron (TSI) agar
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What is the IMVIC a combination of?
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indole, MR, VP, citrate
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What does IMVIC only identify?
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genus
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What does selective media contain?
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components that inhibit the growth of unwanted bacteria thus selecting bacteria that are resistant to the selective components
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What broth is used in selective media?
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selenite F broth
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How is selenite F broth usually incubated?
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aerobically
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what does selenite F broth allow growth of?
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Salmonella species
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What does Selenite F. broth inhibit?
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obligate anaerobes
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What makes a media differential?
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it contains ingredients to elicit a specific biochmeical or physiological response and allow differentiation of groups of organisms
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What does EMB agar allow and inhibit growth of in selective media?
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allows gram negative bacteria growth and inhibits gram positive bacteria growth
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What does Mannitol Salt Agar allow and inhibit growth of in selective media?
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allows growth of staph and inhibits other bacteria
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What are the three possible agars used in selective media?
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EMB, MSA, SS
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What is MacConkey's agar used for?
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to differentiate lactose fermentation --> red/pink colonies
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What is bile esculin agar used for?
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esculin hydrolysis--> black
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What is Mannitol Salt Agar used for?
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Mannitol fermentation--> yellow
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What are the differential media?
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MacConkey Agar, Bile Esculin Agar, Mannitol Salt Agar, Eosin Methylene Blue (EMB)
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What kind of Medium is Triple Sugar Iron?
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Differential
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In TSI agar, what does a yellow butt indicate?
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glucose fermentation
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In TSI agar, what does a yellow slant indicate?
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sucrose and/or lactose fermentation
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In TSI agar, what do air pockets indicate?
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gas production
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In TSI agar, what does a blackening slant indicate?
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hydrogen sulfide produciton
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What does TSI only identify?
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genus (ex. Salmonella-Shigella) of enteric
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What does TSI agar incorporate sucrose for?
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to differentiate between slow lactose fermenters (coliforms) and non-coliforms
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What do lactose fermenters degrade sucrose faster than?
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lactose
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If lactose fermenters degrade sucrose faster than lactose, how fast will they degrade lactose?
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at a slower rate
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What does the enterotube identify?
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genus and species
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How many biochemical tests does the enterotube contain, and how many chambers does it contain?
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15;12
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What are antimicrobials?
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Drugs used to treat infectious diseases
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What is an example of an antimicrobial?
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an antibiotic
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What is an antibiotic derived from?
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living organisms
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What is an organism considered depending on the size of its inhibition zone?
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resistant intermediate or sensitive
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Why are some organisms considred to be resistant even though there is some inhibition?
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because they are not inhibited by therapeutic concentration
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What would higher concentration of antimicrobials cause?
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inhibition of growth and serious side effects
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What is an antibiogram used for?
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to determine the pattern of resistance in order to choose a therapeutic dose of a particular antibiotic that is both effective and has minimal side effects
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What is the Kirby-Bauer Disk Method used for?
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to determine bacterial susceptibility to various chemical agents
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What does the Kirby-Bauer Disk Method not determine?
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if an agent is bacteriostatic or bacteriocidal
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Why must the Kirby-Bauer Disk Method be standardized?
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in order to obtain consisten and reproducibe results.
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What does the Kirby-Bauer Disk Method use?
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a standardized inoculum and a nutrient agar of standard composition
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How is the efficacy of a drug indicated by in the Kirby-Bauer disk Method?
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by the diameter of the zone of inhibition
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Why is teh size of the zone of inhibition not necessarily a measure of degree of inhibition?
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because of differences in diffusion rates of antimicrobial agents
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Even though large molecular weight agents diffuse only a small distance and produce a small zone of inhibition, what might they still be?
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a powerful inhibitor
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How quickly do small molecules diffuse and what do they produce?
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faster and a larger diameter of inhibition zone
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What are examples of small molecules?
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penicillin and ampicillin
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How quickly do large molecules diffuse and what do they produce?
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slower and a smaller diameter of inhibition zone
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What are examples of large molecules?
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polymyxin B and bacitracin
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What are factors that affect the size of the inhibition zone?
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sensitivity of the organism, molecular size and concentration fo the agent, density of the culture, diffusion rate of the agent, size of inoculum, time and temperature of incubation, interactions b/t the antibiotic and medium
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What is the broth dilution method used to determine?
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Minimal inhibitory concentration and minimal bactericidal concentration
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What is minimal inhibitory concentration?
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lowest concentration that prevents visible growth but not killing
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What is minimal bactericidal concentration?
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lowest concentration that prevents visible growth and induces killing
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What do bacteriostatic agents inhibit?
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growth
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What do bacteriostatic agents not do?
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killing and cell lysis
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Why is binding to cellular targets tight in bacteriocidal agents?
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because they do not become free when drug concentration is low, because the drug stays with media during movement
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What do bacteriolytic agents inhibit, induce, and cause?
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inhibit growth, induce killing, and cause cell lysis
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What are the effects of the combination of drugs?
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Synergism and Antagonism
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What is synergism a combination of?
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2 drugs that has more antimicrobial activity than either agent given alone
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What is synergism used for?
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to provide optimal therapy or to lessen the toxicity of individual drugs by reducing the dosage of each drug
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What is antagonism?
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combination drugs will interfere with each others action mechanism
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What is the nitrogen fixation reaction?
|
N2 + 6H + 6e +12 ATp ---via nitrogenase ---> 2NH3 + 12ADP + 12 phosphate
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What does fibrin do?
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forms clots in plasma
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What does fibrin do?
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clots blood plasma without thrombin
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What does (+) sensitivity indicate in the novobiocin test?
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S. epidermis
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What does (-) sensitivity indicate in the novobiocin test?
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S. saphrophyticus
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What are lancefield antigens?
|
carbohydrate antigens located on the cell wall of the beta hemolytic streptococci
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What do antibodies to lancefield antigens detect the presence of ?
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beta-hemolytic strep
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What do we beta-hemolytic antigens to further classify?
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the beta hemolytic strep into serological groups (Lancefield groups)
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What are enterobacteria if they are motile?
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petrichious
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What are the original and reacted color of glucose?
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red/yellow
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lysine decarboxylase?
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yellow/purple
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ornithine decarboxylase?
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yellow/purpose
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H2S?
|
gold/black
|
|
|
indole?
|
gold/red
|
|
|
adonitol?
|
red/yellow
|
|
|
lactose?
|
red/yellow
|
|
|
arabinose?
|
red/yellow
|
|
|
sorbiotol?
|
red/yellow
|
|
|
voges-proskauer?
|
white/red
|
|
|
dulcitol?
|
green/yellow
|
|
|
phenylalanine/deanimase
|
green , gray/black
|
|
|
urea?
|
gold, red/purple
|
|
|
citrate
|
green/blue
|
|
|
What does SS agar select for?
|
Salmonella and Shigella
|
|
|
What does Maconckey agar select for?
|
gram negative bacteria
|
|
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What can TSI show?
|
alkaline reverstion
|
|
|
What is EMB used to test for?
|
lactose fermentation--> pink (weak/lactose); metallic green (strong lactose)
|
|
|
What do bactericidil antibiotics do?
|
prevent growth and induce killing; no cell lysis or rupture; usually does not fall off when drug concentration decreases
|
|
|
What do bacteriolytic antibiotics do?
|
induce killing by cell lysis, observed as decrease in cell numbers or in turbidity when the agent is added
|
|
|
What do bacteriostatic antibiotics do?
|
growth is inhibited, no killing occurs, E.g. inhibitors of protein synthesis by binding to ribosomes, binding to target site isn't tight; agent becomes free when drug concentration decreases
|
