Optimum isolation conditions of beta haemolytic streptococci

ABSTRACT

The current study was carried out on 50 patients with symptoms of acute pharyngotonsillitis. Throat swabs were inoculated on 5% sheep blood agar plates and incubated in various atmospheric conditions to estimate optimum isolation conditions of beta-hemolytic streptococci. Strict anaerobic conditions were superior for isolation of both group A and non-group A beta-hemolytic streptococci when compared to aerobic conditions, microaerophilic states induced by stabbing blood agar plates or to incubation in an atmosphere enriched with 5-10% CO2. Anaerobiosis was the most sensitive means of isolation of the clinically relevant group A strains. This high sensitivity was not coupled with high specificity as this method permitted the growth of non-group A strains. The use of bacitracin disk sensitivity test is a simple and sensitive to identify group A strains. The combination of the previous two means seems to be the best option to characterize group A beta-hemolytic streptococci