Systematic Veterinary Bacteriology and Mycology

CULTURAL CHARACTERISTICS

• It is an aerobe and facultative anaerobe, growing best at a temperature of 37°C. They grow best in media enriched with blood, serum and fermentable carbohydrates.
• On blood agar after incubation for 24hrs small, circular, semitransparent colonies with an area of clear haemolysis are produced.
• Virulent strains from fresh isolates produce matt (finely granular) colony and avirulent strains form glossy colonies. Strains producing capsules form mucoid colonies.
• In glucose or serum broth, growth occurs as a granular turbidity with a powdery deposit. No pellicle is formed.
• In Edwards’s medium (selective media) it produces dewdrop like black colonies.
• Edwards medium containing blood agar, crystal violet and aesculin (differentiate among different species of streptococci which do or do not hydrolyse aesculin).
• S. pneumoniae is alpha haemolytic, produces mucoid or flat colonies with smooth borders and a central concavity after 48-72hrs on blood agar (draughts man colonies).
• Ability to grow in 0.1 % tellurite broth is characteristic of S. faecalis. Majority of streptococcal species do not grow on Mac Conkey agar except Enterococcus faecalis.