Laboratory Workup of Gram POS Rods

  • Actinomyces

  • Arcanobacterium

  • Bacillus

  • Bifidobacterium

  • Clostridium

  • Corynebacterium

  • Erysipelothrix

  • Eubacterium

  • Gardnerella

  • Lactobacillus

  • Listeria

  • Mycobacterium (other than M. tuberculosis)

  • Nocardia

  • Propionibacterium

MOST MEDICALLY RELEVANT:

  • BACILLUS

  • CLOSTRIDIUM

  • CORYNEBACTERIUM

  • LISTERIA

  • +/- 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

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High Yield Properties of Other Gram POS Rods

 

Spore

Forming

Spore

Formers

 

Non-Spore

Forming

 

Motile

Motility

Properties

 

Non-Motile

 

Gamma

Hemolysis

Hemolytic

Properties

 

Beta Hemolysis

 

Catalase POSITIVE

Catalase

Testing

Catalase

Testing

 

Catalase NEGATIVE

 

Starch Hydrolysis

POSITIVE

Catalase

Testing

Starch Hydrolysis Test

 

Starch Hydrolysis NEGATIVE

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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These posts contain high yield information collected from various educational resources including textbooks, journal articles, educational websites and more. They are intended for educational use only and should NOT be taken as medical advice. I strongly believe the spreading of knowledge and depth of learned information should be encouraged in today's society rather than coveted. Membership is required to view these posts  and should be used solely for educational purposes only.