Streptococcus Pyogens: Morphology,Transmission, Antigenicity and Lysogeny

Both are catalase positive. This is the incorrect pair: S. aureus is catalase-positive, but S. pyogenes (like all streps) is catalase-negative. This is an important point in diagnosis in the lab. 

Ans is ‘a’ i.e., Gram positive cocci

Streptococcus pvogenes  Gram postive cocci

–       Arranged in chains

–       Non sporing

–       Fresh isolates form capsule which is made up of hyaluronic acid. It protects the organism from phagocytosis

–       Cultural characteristic

.  Virulent strains produce ‘matt’ (finely granular) colony

.  Avirulent strains produce ‘glossy’ colonies.

.    Capsulated strains produce mucoid colonies, corresponding in virulence to the matt type.

–  Senstivity to bacitracin is employed as a convenient method for differentiating str. pyogenes from other hemolytic streptococci (Maxted’s observation).

–  Biochemical reactions

.   Catalase negative

.   Not soluble in 10% bile

.   Hydrolyse PYR

.   Ferment trehalose but not ribose.

–   Longest chain is formed by Str. salivarius which is non pathogenic.

– Capsule of grp A & C streptococci is composed of hyaluronic acid, while grp B & D streptococci have polysaccharide capsule.

Ans. is ‘d’ i.e., Resistant to bacitracin

• Streptococcus pyogenes is bacitracin sensitive.
• All other options are correct.

Ans. is ‘c’ i.e., Catalase positive

Streptococcus pyogenes (group A streptococci) are gram-positive cocci arranged in chains. Chain formation is due to cocci dividing in one plane only and daughter cells failing to separate completely. Chain formation is more pronounced in broth media.

• Fresh isolates form capsule which is made up of hyaluronic acid. It protects the organism from phagocytosis

Cultural characteristics

• Virulent strains produce ‘matt’ (finely granular) colony
• Avirulent strains produce ‘glossy’ colonies.
• Capsulated strains produce mucoid colonies, corresponding in virulence to the matt type.

Biochemical reactions

• Senstivity to bacitracin is employed as a convenient method for differentiating str. pyogenes from other hemolytic streptococci (Maxted’s observation).
• Catalase negative
• Not soluble in 10% bile.
• Hydrolyse PYR
• Ferment trehalose but not ribose.

Ans. is ‘c’ i.e., Pili

Virulence factors of str. pyogenes

Str. pyogenes forms several exotoxins and enzymes which contribute to its virulence, but M protein is the most important of these.

Ans. is ‘a’ i.e., Bacitracin

Senstivity to bacitracin is employed as a convenient method for differentiating str. pyogenes from other hemolytic streptococci (Maxted’s observation).