Microbiology in pictures

Streptococcus pyogenes
Group A streptococcus

Streptococcus pyogenes on blood agar plate

Streptococcus pyogenes on Columbia agar with 5% sheep blood. Cultivation 24 hours, in an aerobic atmosphere enriched with 5% carbon dioxide. Colonies are surroundend by a wide zone of beta-hemolysis. Most strains are susceptible to erythromycin (macrolides) and clindamycin (lincosamides) - fig. B. Positive PYR test is useful for preliminary identification of isolated strains (together with negative catalase test). Identification is confirmed by latex aglutination.


S. pyogenes is the cause of many important human diseases, ranging from mild superficial skin infections to life-threatening systemic diseases. Infections typically begin in the throat or skin. Examples of mild S. pyogenes infections include pharyngitis ("strep throat") and localized skin infection ("impetigo"). Erysipelas and cellulitis are characterized by multiplication and lateral spread of S. pyogenes in deep layers of the skin. S. pyogenes invasion and multiplication in the fascia can lead to necrotizing fasciitis, a potentially life-threatening condition requiring surgical treatment. Infections due to certain strains of S. pyogenes can be associated with the release of bacterial toxins. Throat infections associated with release of certain toxins lead to scarlet fever. Other toxigenic S. pyogenes infections may lead to streptococcal toxic shock syndrome, which can be life-threatening. S. pyogenes can also cause disease in the form of postinfectious "nonpyogenic" (not associated with local bacterial multiplication and pus formation) syndromes. These autoimmune-mediated complications follow a small percentage of infections and include rheumatic fever and acute postinfectious glomerulonephritis. Both conditions appear several weeks following the initial streptococcal infection. Rheumatic fever is characterised by inflammation of the joints and/or heart following an episode of streptococcal pharyngitis. Acute glomerulonephritis, inflammation of the renal glomerulus, can follow streptococcal pharyngitis or skin infection.

Abbreviated from Wikipedia.

description image
GRAM-POSITIVE COCCI
NONMOTILE
NONSPOREFORMING
CATALASE: NEGATIVE
OXIDASE: NEGATIVE
FACULTATIVELY   ANAEROBIC

BASIC TESTS
FOR IDENTIFICATION

beta-hemolysis:+
catalase test:-
PYR test:+
bacitracin test:
(+ = susceptible)
+
Lancefield's group A antigen+

ANTIBIOTIC
TREATMENT

Penicillin

ALTERNATIVES:

Other beta-lactam antibiotics
(e.g., amoxicillin, cefpodoxime, cefazolin, cefotaxime)

Macrolides

Clindamycin
list of anntibiotics

 

 
Gram-positive cocci drawing

COLONY MORPHOLOGY

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streptococcus pyogenes streptococcus pyogenes    
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Streptococcus sp.

Streptococcus pyogenes

Rheumatic fever

Necrotizing fasciitis

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Pathophysiology

Epidemiology

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SKIN INFECTIONS
 
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