Not true about streptococcus pyogenes ?
Gram positive
Bacitracin sensitive
Catalase positive
Not soluble in bile
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.