Advantages of Blood Agar-NaCl Selective Medium in the Isolation of Beta-Hemolytic Streptococci from Throat Swabs

The detection of beta-hemolytic streptococci (BHS) from throat swab (TS), especially Streptococcus pyogenes, in diagnostic or epidemiologic purpose is usually accomplished on an unselective medium, agar with 5% sheep blood. The false negative results which might occur, with an important frequency, justify the microbiologists’ interest for the improvement of the isolation conditions: improvement of the basic medium quality, incubation in anaerobic atmosphere for 48 hours, the use of a certain selective media, which would suppress the normal pharyngeal flora that makes the BHS detection difficult and almost impossible.1, 2, 6, 7 In this paper we studied the comparative efficiency of two selective media and of the usual unselective medium in the isolation of BHS from TS taken from children.