奶牛乳腺炎金黄色葡萄球菌耐药基因型和表型的相关性分析

Correlations of the antibiotic-resistant genetype and phenotype of Staphylococcus aureus isolated from bovine mastitis

为研究奶牛乳腺炎金黄色葡萄球菌耐药基因型和表型的分布,并对其相关性进行分析,采用PCR方法对从奶牛乳腺炎乳样中分离的33株金黄色葡萄球菌进行耐药基因检测,采用微量肉汤稀释法测定其对7种药物的敏感性。PCR结果显示,fos A、erm B、erm Cb、aph(3′)-IIIa和lin A/A′基因的检出率分别为51.52%、87.88%、100%、100%和6.06%;未检测到mec A、fos B、fos C、tet M、erm Ab、msr A、msr B、mef A、aac(6′)-Ie+aph(2″)、ant(4′)-Ia、van A、van B、van C1、van C2/3等14种耐药基因。药敏试验结果显示,金黄色葡萄球菌对磷霉素最为敏感,敏感率高达100%,磷霉素可作为临床备用药物;对红霉素的耐药现象最为严重,达到了93.94%;对氨苄西林和克林霉素的耐药率均达到72.73%。相关性分析表明,fos B、fos C基因型和磷霉素耐药表型一致;红霉素耐药占比为93.94%,与erm B基因(87.88%)、erm Cb基因(100%)比较接近。

In order to investigate the correlations of the antibiotic-resistant genotype and phenotype distribution of Staphylococcus aureus isolated from the mastitic milk samples,PCR assay was used to identify the presence of antibiotic-resistant genes and 96-well plate microdilutioon method was adopted to test the susceptibility 33 Staphylococcus aureus strains to 7 antibiotics. The PCR results revealed that the positive rate of genes fosA,ermB,ermCb,aph（3＇）-IIIa and linA/A＇were 51.52%,87.88%,100%,100%and 6.06%,respectively. Other 14 antibiotic resistant genes,including mecA,fosB,fosC,tetM,ermAb,msrA,msrB,mefA,aac（6′）-Ie＋aph（2″）,ant（4′）-Ia,vanA,vanB,vanG1,van2/3, were not found. As all isolates were sensitive to fosfomycin,we recommend this antibiotic as candidate for clinic use. However,the proportion of erythromycin-resistant isolates was as high as 93.94%,and there were also 72.73% isolates that were insensitive to clindamycin and ampicillin,which indicates these 3 antibiotics are not good choices to cure bovine mastitis caused by Staphylococcus aureus. Phenotype of fosfomycin-resistant （0） was well correlated with fosB （0） and fosC （O）.In addition, phenotype of erythromycin-resistant （93.94%） was positively correlated with ermB （87.88%） and ermC（100%）.However,there were no obvious corresponding relationships between the other genotypes and the other phenotypes.