BIOCHEMICAL TRAITS AND ANTIMICROBIAL SUSCEPTIBILITY OF STREPTOCOCCUS-SUIS ISOLATED FROM SLAUGHTERED PIGS

A total of 522 Streptococcus suis isolates were recovered from the ton sils of slaughtered pigs by culturing on media containing different sp ecific antisera. The serogroup reactions were determined by coagglutin ation. The most frequently isolated serotype was serotype 4 (represent ing 28.7% of the isolates), followed by serotype 3 (24.9%) and serotyp e 2 (22.6%). Typable isolates were examined by growth in 6.5% NaCl, am ylase activity, acetoin production, susceptibility to optochin and pro duction of acid from mannitol, melibiose, raffinose, salicin, sorbitol and trehalose. Finally, all isolates were tested for antimicrobial su sceptibility against ampicillin, cephalotin, lincomycin, neomycin, pen icillin, spiramycin and trimethoprim-sulphamethoxazole using the disk- diffusion technique. All isolates were amylase-positive and acetoin-ne gative, and failed to grow in 6.5% NaCl broth. Nine isolates were opto chin-susceptible. Moreover, 10 isolates produced acid from mannitol, 2 1 produced acid from sorbitol, and 36 and 37 did not produce acid from salicin and trehalose, respectively. Six salicin- and trehalose-negat ive isolates and two mannitol- and sorbitol-fermenting isolates were f ound. Biochemical differences between serotypes were not observed. The most active drugs against S. suis were the beta-lactam antibiotics, a lthough only 83.3%, 70% and 78.5% of isolates were susceptible to ampi cillin, cephalotin and penicillin, respectively. Half of the isolates were resistant to trimethoprim-sulphamethoxazole, and resistance to li ncomycin, neomycin and spiramycin appeared to be very high.