Biological Study On Pathogenic Streptococcus Suis Anhui Isolates

Swine streptococcosis is the general term of pig diseases caused byStreptococcus suis, Streptococcus equi subsp. zooepidemicus,Streptococcus equisubsp.equisimilis and streptococcus of Lancefield grouping D, E，L,with the mainsymptoms of lymph node abscesses,meningtis,arthritis,endocarditis and septicemia.S.suis is the most important pathogen of swine streptococcosis worldwide. Thebiological characteristics of S.suis have regional differences. In this study, thedistribution of serotype and virulence genotype, pathogenicity, antibiotic resistanceand other biological characteristics of49Streptococcus suis strains isolated fromAnhui area were detected and analyzed.The morphology, cultural characteristics and hemolytic of Streptococcus suisstrains isolated from Anhui area were initially studied of by observing colonygrowth characteristics and Gram staining.46of49strains’ morphology, dyeing andcultural characteristics are coincidence with Streptococcus suis.49strains renderdifferent hemolytic on the rabbit blood agar. The hemolytic titer of19S.suis2strains was tested by microELISA. The results showed that β-hemolytic strains arewith higher hemolytic titer.Streptococcus suis serotype1,2,7and9were identified by PCR technology.The percentage of Streptococcus suis serotype1,2and7is38.8%,16.3%and14.3%respectively. There is no Streptococcus suis serotype9strains detected. That swinein Anhui province is infected by several serotypes S.suis，in which S.suis2is thedominant serotype.Primers according to references were used to detected mrp, epfand sly gene by PCR. The result shows that the positive rate of mrp, epf and sly geneis36.7%,38.8%,71.4%respectively. PCR methods for detecting4virulence genesof S.suis2were developed based on the specific primers for virulence gene of cps2J,mrp, epf and sly.Then the four kinds of virulence genes amplified fragments weresequenced and analysised. The result shows that the homology of cps2J, mrp, epfand sly genes within S.suis2Anhui isolates and isolates referenced are higher than98.3%,99.2%,87.8%and99.0%, respectively.The analysis found that thedistribution of virulence genes of S.suis Anhui isolates are similar with other areareported.CPS,MRP,EPF and SLY are important virulence factor in Anhui area.The antibiotic resistance on25kinds of antibiotic used commonly was detectedby Kirby-Bauer disc agar diffusion method for Streptococcus suis Anhui isolates. Most of the strains tested are more sensitive to amoxicillin, ampicillin, rifampicinand cephalothin V with95.92%,93.88%,85.71%and81.63%sensitive raterespectively. And bacitracin and tetracycline have higher antibioticresistance,87.76%and85.71%respectively. Multiple antibiotic resistance analysisshows that the resistance is very serious. The most common multi-antibioticresistance spectrum is Bacitracin–Tetracycline–Doxycycline-Sulfamethoxazole.It shows that the antibiotic resistance of S.suis Anhui isolates is very serious.The median lethal dose (LD50) of five S.suis2strains was determined by Cole’smethod.Strain HJ17with β-hemolytic, higher hemolytic(1:64) and virulence genotype ofmrp+/epf+/sly+has the highest toxicity(1.38×107CFU for LD50).It suggested that thevirulence of S.suis2is affected both by the hemolytic and virulence factor carried ofstrains.