| Staphylococcus aureus(S.aureus)is an important human etiologic agent,which can cause a wild range of diseases.It can also lead to food poisoning.Food poisoning because of S.aureus contamination is ranked third worldwide.Due to the unreasonable use of antibiotics,the resistant strains of S.aureus appeared,which had a huge influence on human health.According to the resistance to methicillin,S.aureus can be divided into methicillin-resistant Staphylococeus aureus(MRSA)and methicillin-sensitive Staphylococcus aureus(MSSA).The pathogenicity of S.aureus is related to the virulence factors that it has.S.aureus that from different regions and sources has different popular genotypes.Researching the characteristics of popular genotype can provide reference for the prevention.Objective 1.To understand the characteristics of drug resistance and virulence genes of S.aureus from different kinds of food,and to compare the differences of those characteristics between the food strains and hospital strains.2.To compare the drug-resistant patterns and virulence genes carried in MRSA and MSSA strains,and analyze the SCCmec genotypes of MRSA strains.3.To understand the agr types of S.aureus,and compare the differences of virulence genes between different types.4.To investigate the popular spa types of S.aureus,and understand the epidemic characteristics of S.aureus in our region.Methods 1.The drug resistance was based on minimum inhibitory concentration.2.The resistance and virulence genes of S.aureus were amplified by PCR.3.The multiplex PCR was used to analyze the SCCmec genotypes of MRSA strains.4.The multiplex PCR was used to analyze the agr types of S.aureus.5.Spa types were analyzed by PCR.The amplified products were sequenced.Spa types were analyzed based on the features and orders of repeat sequences.6.Statistical analysis was performed by SPSS 21.0.The chi-square test was used to analyze the differences between the rates of resistance phenotype,resistance and virulence genes carried in MRSA and MSSA strains.Results 1.All strains were sensitive to vancomycin.The strains that from hospital and fresh meat and rice products were resistant to seven antibiotics,while that from meat products and fruits and vegetables were resistant to six antibiotics.Compared with food isolates,the drug resistance rates of penicillin,erythromycin,clindamycin,ciprofloxacin and gentamicin were significantly higher in hospital strains,and the positive rates of resistance genes such as acc(6’)/aph(2’’),aph(3’)-III,erm A,erm B and tet M were also higher in hospital strains,but the positive rate of ant(4’,4 ’’)was lower than that in food isolates.The positive rates of virulence genes such as sea,seb,pvl and etb were significantly higher in hospital strains,while hla and hlb were significantly higher in food strains.2.The total detection rate of MRSA was 34.18%.The rates of MRSA were 37.84% in hospital strains and 29.92% in food isolates.There was no significant difference between the two sources.Among the strains of food origin,the rates of MRSA were 40.00% in fresh meat,17.65% in meat products,11.11% in fruits and vegetables,29.73% in rice products,respectively.Compared with MSSA strains,the resistance rates of erythromycin,clindamycin,ciprofloxacin,gentamicin and tetracycline in MRSA were significantly higher,and the positive rates of resistance genes such as erm A,msr A and tet M in MRSA were also higher,while the rates of virulence genes had no statistical difference between the MRSA and MSSA strains.3.There were three SCCmec genotypes in MRSA strains,of which SCCmec type Ⅲwas the most common type,detected in 62.77%,followed by SCCmec type Ⅳa(15.96%)and SCCmec typeⅡ(2.13%).And 18 strains were not classified.The proportion of SCCmec type Ⅲ all was the highest in the hospital and food sources.4.Among the 275 strains,the order was agr groupⅠ,Ⅱ,Ⅲand Ⅳ,presented in 60.73%,16.36%,14.91% and 4.00%,and there were 11 isolates with negative result for any of the four agr groups.5.The main spa types in hospital isolates were t030 and t437,while in food isolates were t002 and t091.In our study,SCCmecⅢ-t030-agrⅠand SCCmecⅣa-t437-agrⅠ were the most common types in MRSA isolates,while in MSSA were t002-agrⅡ and t189-agrⅠ.Conclusions 1.The phenomenon of drug resistance in S.aureus was widespread.Different kinds of food strains had different resistance and virulence characteristics.Compared with food isolates,the drug resistance was more serious in hospital strains.2.Compared with MSSA strains,the multiple drugs resistance were more obvious in MRSA.The rates of resistance genes were also higher,while the rates of virulence genes had no difference.The popular type of SCCmec genotypes in MRSA strains was SCCmec type Ⅲ.3.The highest proportion in S.aureus was agr typeⅠ,followed by type Ⅱ,type Ⅲ and type Ⅳ,different agr types had different virulence genes.4.There had different popular spa types from different regions,and there were some links between the spa type and agr type. |
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