8/12/2019 Notes on Aerobic G(+)

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Notes on Aerobic Non-Spore-forming Gram-Positive Bacilli

1.

Listeria monocytogenes

a.

Causes spontaneous abortion and meningitis in animals (e.g. sheep)

b.

Found in the environment (soil and water), and is normal flora of vagina and intestines in humans.

c.

L. monocytogenescauses a variety of infections in neonates, pregnant women, and immunosuppressed

patients. Meningitis is common outcome of infection.

d.

Identifying characteristics

1.

L.monocytogenesgrows on most media; colonies are small and white with a narrow zone of beta-

hemolysis.

2.

Closely resembles group B streptococci on SBA

3.

L.monocytogenesdemonstrates both umbrella motility in semisolid media at RT and end-over-end

(tumbling) motility in a wet mount

4.

HIppurate hydrolysis, CAMP test, esculin, catalase positive

2.

Arcanobacterium

a.

6 species has been named, 3 are clinically significant:A.haemolyticum, A.pyogenes, andA. bernardiae

b.

Natural habitat of these bacteria has not been confirmed, although A.haemolyticum has been associated

with pharyngitis and wound and tissue infections. A.pyogenes is found on mucous membranes of cattle,

sheep, and swine and is linked to abscess formation, wound, and soft tissue infections in cattle and humans.

c.

The clinically significant Arcanobacterium spp. form small beta-hemolytic colonies on SBA and are catalase

negative and nonmotile.

d.

A.haemolyticum can be identified by the CAMP inhibition test. This bacterium produces phospholipase D,

which inhibits the activity of the Staphylococcus aureus beta-lysin. Corynebacterium pseudotuberculosis

also exhibits this phenomenon.

3.

Erysipelothrix rhusiopathiae

a.

E.rhusiopathiae primarily infects animals. Humansgenerally become infected through contact with infected

animals (occupational exposure) or rarely by consuming infected meat.

b.

Human infections often result in cellulitis(erysipeloid lesions that can resemble erysipelas caused byStreptococcus pyogenes) but may also present as bacteremia or endocarditis.

c.

Identifying characteristics

1.

Nonmotile, pleomorphic gram-positive bacilli

2.

Catalase negative

3.

Hydrogen sulfide positive

4. Nocardia asteroides

a. generally found in immunocompromised patients with chronic pulmonary disorders

b. N. asteroides is the most clinically relevant species; other species include N.brasiliensis and N.otitidiscavium

c. Identifying characteristics1. pleomorphic, branching gram-positive bacilli in chains that produce a beading arrangement, appear

Fungal-like

2. partially acid-fast, catalase positive, nonmotile

3. requires up to 6 weeks for growth

4. exudate contains masses of filamentous organisms with pus that resemble sulfur granules.