Antibiotic-resistance And Typing Of Staphyloccocus Aureus Isolated From Animals In China

Staphyloccocus aureus is a kind of Gram-positive coccus and universally distributed in nature. It can infect human and animals and is a kind of important zoonosis pathogen. Public health and food safety are heavily threatened because of its enterotoxin which can contaminate food and leads to food poisoning of human The number of antibiotic-resistant strains, especially methicillin-resistant Staphyloccocus aureus (MRSA) strains, have beeing increased recently, which make clinical treatment more difficult. To study antibiotic-resistance of Staphyloccocus aureus strains of animal origin, we must know the distribution of phenotyping and genotyping of Staphyloccocus aureus and further discriminate prevalent strains and non-prevalent ones and compare the correlations of strains from different regions. Thus this study is significantly important in veterinary medicine and public health.124isolates of Staphyloccocus aureus from different regions and different animals (mainly cows and pigs) were collected from2008to2010. CHROM agar Staphyloccocus aureus Medium was used to prescreening of samples. Then BioMerieux API strip detect and coagulase test was made to identified Staphyloccocus aureus. At the same time, nuc gene was amplified by PCR for further assurance from gene level. The rate of isolation reached to16%.13kinds of antibiotics were selected to test antibiotic-resistance of these isolates by broth dilution method, the result of antibiotic-resistance detection revealed that the postive rate of MRSA(cefoxitin resistant) was27%, mainly from pigs; the resistant rate of ampicillin, penicillin and erythromycin was up to97%,86%and75%respectively; the resistant rate of the other10antibiotics was from50%-0%; no vancomycin-resistant isolate was found. Cefoxitin-resistant isolates were selected to amplify methicillin-resistant gene mecA, the result indicated that all of the strains with mec A gene had phenotype of methicillin-resistance.The serotypes of these isolateswere identified using anti-coagulase serum, the dominant serotypes were type Ⅶ,Ⅵ and combined type, no type Ⅱ and Ⅴ was found,91%of the isolates could be typed.The prevalent seotpyes of strains isolated from cows and pigs were quite different. Coagulase serotypes of isolates from animals in China had more diversity, the distribution of serotypes was relatively centralized. According to serotypes, coa(coagulase) gene was amplified by PCR and sequenced for further being analysed by Mega software. There were six kinds of amplicon which size varied from400bp to1,000bp. Analysis of sequences from36isolates was made to construct the phylogenetic tree of coa gene. This tree revealed the diversity of coa gene and the typing method based on this gene could distinguish strains well.RT(Ribotyping) and MLST(Multilocus Sequence Type) were used to identify genotype of Staphyloccocus aureus isolates. The results of ribotyping revealed that isolates from cows and pigs have different evolution direction in the dendrogram; genetic similarity of isolates belong to the same serotype is from50%to100%. The results of MLST illustrated that all MRSA isolates were ST9, which was the maintypes of Staphyloccocus aureus from animals in China. The MSSA isolates had nine sequence types, including ST398、ST9、ST97.