Investigation On Staphylococcus Aureus Contamination From Different Sources And Studies On Drug Sentivity, Toxic Genes And PFGE Typing

Staphylococcus aureus is a kind of food-borne pathogen, which widely exists in nature.It can cause a lot of diseases for men and animals and trigger tremendous harmfulness inhuman health and animal husbandry. S. aureus can be isolated from different kinds of animalsand food. With the increasing of toxic genes and drug resistance in S. aureus, it becomes moreand more difficult for people to control the break out of food-borne diseases and clinical cureof animal diseases. With the wide spread use of antimicrobials, more and more drug resistancestrains emerged, especially in methicillin-resistant S. aureus (MRSA). Therefore, theresearches on the potential hazards of S. aureus have become the hot topic. Currently, as forthe issue of drug resistance of MRSA, many researchers consider it as the result ofwidespread application of antimicrobials and transfer of some movable elements. However,due to the uncompleted molecular biological study on S. aureus in our country and worldwide,the establishment of genetic profiling of S. aureus is still required certain time. Hence, theepidemic researches on S. aureus require going further and the identification and tracing of S.aureus in different resources is particularly critical. In this research, we collected1152samples of chicken meat from4provinces in china (Shaanxi, Guangdong, Fujian andGuangxi),400samples of ready-to-eat salads from10cities in Shaanxi province,387samplesof milk powders from12cities in Shaanxi province,295raw milk samples (sub-clinicalmarmites samples and marmites samples) from10cattle farms in Shaanxi province and400samples of swine nasal strips for study. Firstly, the positive strains from the samples wereisolated and identified to study the distribution of S. aureus in different kinds of samples.Then, the positive samples were selected. The drug sensitivity tests were conducted by theagar dilution method, and some common toxin genes (SEs, PVL, TSST-1) and drug resistancegenes were detected with PCR method. Through the comparison of drug sensitivity, toxingenes and drug resistance genes of strains derived from animal and food, and gene typing ofthose strains with PFGE method, the “gene map” of those S. aureus was obtained. The dataprovide a basis for the monitoring of S. aureus by tracking and tracing the sources. The resultsof this research are as follows: 1We totally isolated57,23,62,210,29,25and71positive strains from the collected samplesof mastitis milk, raw milk, pig nasal strips, chicken, milk powder, rice powder andresdy-to-eat food. The rates of the isolation were32.39%,19.33%,15.5%,18.23%,20.28%,10.25%and17.75%, respectively. The detection rates of mecA gene in mastitis milk, pignasal strips, chicken and ready-to-eat food were10.53%,16.87%,3.76%and6%, respectively,while there was no mecA gene strain isolated from raw milk, milk powder and rice flour.2The results of drug sensitivity tests showed that all the S. aureus detected were sensitive tovancomycin, amikacin and cefoperazone, the resistance rates of the strains to erythromycinand trimethoprim are the highest, the resistance to other six kinds of antimicrobials has certaindegree, the resistance rates are not high. Among all the samples, the resistance of S. aureusfrom swine samples is higher than that from other sources of samples, while the chickensample has the widest spectrum. They show certain degrees of resistance to nearly all kinds ofantimicrobials except Vancomycin and Amikacin.3The results of PVL and SEs genes tested by PCR method showed that the isolation rates ofPVL in mastitis milk, raw milk, pig nasal strips, chicken, milk powder, rice flour andresdy-to-eat food were27.5%,85%,50%,17.5%,55%and5%, respectively, and the isolationrates of the SEs in mastitis milk, raw milk, pig nasal strips, chicken, milk powder, rice flourand resdy-to-eat food were80%,72.5%,0,27.5%,65%and50%.There were55plants wereisolated which harboured both genes. All samples have not been detected the presence oftoxic shock toxin and exfoliate toxin.4According to PFGE typing,we found a total of66different genotypes, and got21geneclusters with80%similarity analysis. When we analysed of S. aureus from different sourcesseparately, we found that S. aureus from mastitis milk can be divided into16genotypes andthree gene clusters with80%similarity analysis; S. aureus from raw milk can be divided into15genotypes and5gene clusters with80%similarity analysis; S. aureus from pig nasal stripcan be divided into19genotypes and six genotypes with80%similarity analysis; S. aureusfrom milk powder and rice flour can be divided into20genotypes and nine genotypes with80%similarity analysis; S. aureus from ready-to-eat food can be divided into26genotypesand eight genotypes with80%similarity analysis.