| Staphylococcus aueus(SA)is one of the main causes of community-and hospitalacquired infections.It has different virulence factors and toxins and can cause a variety of diseases.S.aureus can be colonized in humans,animals and their products.Livestock is an important repository for S.aureus.People can infect S.aureus by touching infected animals or their products.The presence of S.aureus poses a threat of zoonotic infection to humans and animals.The improper use of antibiotics has resulted in an increase in resistance to S.aureus,resulting in methicillin-resistant S.aureus(MRSA).The resistance of MRSA strains to antibiotics is a major challenge to public health.In recent years,the synergistic effect of antibiotics and heavy metals has caused widespread concern.In this study,yak nasal swabs,fur swabs,and environmental swabs were sampled during yak slaughter to isolate and identify S.aureus and also to investigate its epidemiology.Further,the effects of copper sulfate solution continuous induction on the antibiotic resistance and the expression of related resistance genes of MRSA isolates were investigated.The main findings are as follows:(1)A total of 1069 samples were collected and 526 S.aureus strains were isolated with a total detection rate of 49.20%.Among them,nasal swabs(310/682,45.45),fur swabs(137/215,63.72%),and environmental swabs(79/172,45.93%).The strains carried of 7 enterotoxin genes in total.In the detection of traditional enterotoxin and new enterotoxin,sea(12.17%)and selx(79.66%)had the highest;four other virulence genes were detected,hl?(43.35%)and hl?(31.94%)with the highest detection rate;three anti-disinfectant genes were also detected,and qac H gene was not detected;five anti-heavy metal resistance genes were detected,and 91.63% of the strains carried two or more anti-heavy metal genes.(2)Nine MRSA strains were identified by PCR and mecA sequencing alignment analysis.All nine MRSA strains were isolated from the yak nasal cavity.The main type of MRSA is SCCmec IVa-ST88-t1376.MRSA strains carried a total of 8 antibiotics genes.The sensitivity of MRSA to 24 antibiotics was tested by the K-B method,and the multidrug resistance rate of all 9 MRSA strains was found to be 100%(resistant to 3 or more antibiotics).The MICs(Minimum inhibitory concentration)of MRSA strains to copper sulfate,zinc chloride,benzalkonium bromide,peracetic acid,glutaraldehyde and sodium hypochlorite were determined by using the standard broth microdilution method.It was found that MRSA strains were susceptible to copper sulfate,zinc chloride,benzalkonium bromide,and peracetic acid;but not sensitive to glutaraldehyde and sodium hypochlorite.(3)In the experiment of 1/4 MIC copper sulfate solution to be used to continuously induce MRSA strains,the MICs of MRSA strains to copper sulfate,zinc chloride,benzalkonium bromide,peracetic acid,glutaraldehyde,sodium hypochlorite,ampicillin,oxacillin,cefoxitin,ofloxacin,roxithromycin and streptomycin were determined by using the standard broth microdilution method.And the changes of the antibiotic resistance map of MRSA strains were determined.After continuous induction by copper sulfate solution for 7 days,the MIC values to copper sulfate solution increased for MRSA strains;especially the MIC values of ?-lactam antibiotics changed significantly before and after induction(P<0.05).There was no significant change of the MIC values for MRSA strains to other six antibiotics.(4)At the same time,a quantitative real time-PCR was applied to monitor relative expression levels of anti-heavy metal genes(cop A,ars B),antibiotic resistance genes(mecA,nor A,erm B,aac6'/aph2''),virulence genes(hl?)and enterotoxin gene(seb,sem).7 days later,the expression of the anti-heavy metal genes,related antibiotic resistance genes,virulence genes and enterotoxin gene for the MRSA strains were significantly up-regulated(P<0.05).Copper sulfate solution has a strong synergistic effect on the antibiotic resistance of MRSA strains. |
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