Isolation and characterization of Streptococcus suis from pig farms in Sichuan

Abstract

In this experiment, bacteria were isolated by aseptically collecting tissue samples of heart, spleen, liver, lymph node, and joint fluid from diseased and dead pigs, and were identified by colony morphology observation, Gram staining microscopy, biochemical experiments, PCR identification, pathogenicity test, and drug sensitivity test. The results showed that the isolated strains were Gram-positive, long-chained, or bipartite coccoid bacteria. It could ferment most sugars, and the VP test and indigo substrate test were negative, consistent with the physiological characteristics of Streptococcus suis. The PCR method was used to identify the serotypes, and about 500 bp of podocarp serotype 9-specific bands could be amplified. Pathogenicity test showed that mice became depressed 6h after intraperitoneal inoculation with the isolate, and died within 24h after rapid breathing, slow movement, and loss of appetite. The results of the drug sensitivity test showed that the isolate was highly sensitive to cefthiophene, florfenicol, cefadroxil, ciprofloxacin, ampicillin, amoxicillin, highly sensitive to sulfisoxazole, polymyxin B, enrofloxacin, doxycycline, and showed resistance to lincomycin, kanamycin, neomycin, gentamicin.