Abstract: Streptococcus suis was one of the most frequent pathogenic bacteria which had caused a serious of problems in pig industry all over the world. Therefore, it was important to evaluate the resistance to antibiotics and the distribution of tetracycline resistance determinants in Streptococcus suis from pigs in order to prevent and control this diseases. All Streptococcus suis were isolated from clinically diseased pigs and antimicrobial susceptibility to 18 antibiotics was performed by Kirby-Bauer and broth microdilution method. The results showed that most of the SS isolates showed resistance to tetracycline,sulfamethoxazole and gentamicin.Especially, a high level of resistance was found for tetracycline(98.2%);the isolates were susceptible to cephalosporins,all isolates showed multiple-drug resistance, resistance to 6 and 14 antibiotics was the main trend, the percentage were 20% and 17%, respectively.Four pairs of primers were designed to detect the presence of tetracycline resistance gene taken by SS.The results showed that most of the SS had tetracycline drug resistance gene tetM(85.71%),which indicated that tetM might be one of the main molecular mechanisms mediated the resistance of the SS isolates from Guangdong to tetracycline.

Key words: Streptococcus suis; antimicrobial susceptibility; tetracycline resistance gene