Laboratory Workup of Gram POS Rods
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Actinomyces
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Arcanobacterium
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Bacillus
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Bifidobacterium
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Clostridium
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Corynebacterium
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Erysipelothrix
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Eubacterium
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Gardnerella
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Lactobacillus
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Listeria
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Mycobacterium (other than M. tuberculosis)
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Nocardia
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Propionibacterium
MOST MEDICALLY RELEVANT:
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BACILLUS
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CLOSTRIDIUM
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CORYNEBACTERIUM
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LISTERIA
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+/- MYCOBACTERIUM
There are many gram positive bacilli organisms. However, the four most medically relevant ones encountered are bacillus, clostridium, corynebacterium & listeria. These can be differentiated from one another according to unique chemical and biological properties of the various organisms. We will cover some of the laboratory testing methods used to identify the various gram-positive organisms.
Most Important
To distinguish between the 4 most medically relevant genera, ask these questions:
-Does it form spores?
Yes vs. No?
-What are its oxygen requirements?
Aerobic vs. Anaerobic?
-Can it move around?
Motile vs. Non-motile?
Bacillus Clostridium Corynebacterium Listeria
???
YES
Capsule= B. anthracis
No capsule= B. cereus
High Yield Properties of Other Gram POS Rods
Spore
Formers
Motility
Properties
Hemolytic
Properties
Catalase
Testing
Catalase
Testing
Catalase
Testing
Starch Hydrolysis Test
Starch Hydrolysis Test
The purpose of the starch hydrolysis test is to determine whether bacteria are able to produce the alpha-amylase enzyme by using starch as a complex hydrocarbon from glucose.
Starch
Amylase enzyme
Blue-black color
NEGATIVE for amylase production
Glucose
No color
POSITIVE for amylase production
Flooding the plate with iodine will turn starch blue-black.
If bacteria produce amylase, starch is digested and these areas will remain clear.
Clearly, a lot of bacillus are positive with the starch hydrolysis test. There are several other tests that can be performed to further classify the bacillus species. However, not important for boards.
The Starch Hydrolysis test can be combined with other tests to differentiate Corynebacterium (POS) from the Lactobacillus family (NEG).
Summary
anaerobes
MICRO & IMMUNO
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