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why is it important to complete morphological and cultural characterizations before pursuing physiological testing?
morphological and cultural characterizations are important to help with preliminary classification and help one decide which tests are appropriate for further identification, rather than to run every test available
what is the relationship between physiological and genetic differentiation of bacteria?
genes are recipes for making cellular proteins, including the enzymes that regulate the cell metabolism. therefore, species with similar enzymatic capabilities will likely have similar genetic makeup
what is the function of bacterial exoenzymes?
bacterial exoenzymes are used for the extracellular degradation of substances so that the simpler compounds can be taken into the cell as nutrient or energy sources
anabolism vs. catabolism
anabolism is the energy driven synthesis of complex molecules from smaller ones. catabolism is the energy releasing degradation of complex molecules into smaller ones
fermentation vs. respiration
fermentation is the metabolism of sugars in the absence of oxygen whereas respiration is a metabolism process that does utilize oxygen
why is the catalase test useful for the differentiation of staphylococci from streptococci?
both are gram positive cocci, however staph are catalase positive and strep are catalase negative
how are acidic or alkaline products detected in culture medium?
both are detected with pH indicators, which are colored dyes that change color in response to pH changes
what are two tests for reactions that produce acid end products?
acid end products are a result of various sugar fermentations and fat hydrolysis
what are two tests for reactions that produce alkaline end products?
alkaline end produces are a result of urea hydrolysis, citrate utilization and proteolysis (litmus milk, kliglers agar)
what types of gases can be produced as a result of sugar fermentation?
carbon dioxide and hydrogen gas may be produced
how are gases produced by sugar fermentation detected in reactions?
in a durham tube as a trapped air bubble or as an air pocket in a stabbed solid medium
what is a nonfermentative test in which gas production indicates a positive test result?
the catalase test yields oxygen gas as a positive result
how do the methods for detecting the differences between starch, casein, and triglyceride hydrolysis differ?
hydrolysis of casein in milk is readily visualized as the opaque milk agar shows clear zones of hydrolysis. because starch is not readily visible in starch agar, iodine is added to form complexes and reveal the clear zones of hydrolysis. detection of fat hydrolysis is performed indirectly. instead of visualizing the absence of the substrate, spirit blue agar contains a pH indicator that reveals the release of fatty acids
which hydrolysis test would have a positive result for propionibacterium acnes? why?
a positive triglyceride hydrolysis test is expected because it feeds on oil in clogged glands
which hydrolysis test would have a positive result for helicobacter pylori? why?
a positive urea hydrolysis test is expected because one of the byproducts of this reaction, ammonia, will neutralize harmful stomach acid and allow the bacterium to survive in this hostile environment and cause infection
what components of kligler's agar and sim media are included?
cysteine, an organic sulfur containing substrate, and ferrous salts, which complex with hydrogen sulfide to produce a black precipitate for identification
what are the reasons for stabbing kligler's agar and sim media?
sim is a semi solid medium that is stabbed to determine motility. kligler's iron agar is a solid that is stabbed to create an anaerobic environment to test for glucose fermentation
what difficulties does one encounter when trying to differentiate bacteria on the basis of physiological tests?
differentiation of bacteria based upon physiological tests can be difficult because many tests need to be conducted in order to find the few differences that closely related organisms might have between them
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