葡萄球菌中两类D试验阳性表型及基因分析

目的研究葡萄球菌中红霉素对克林霉素的诱导耐药表型及基因型。方法对116株金葡菌和凝固酶阴性葡萄球菌进行红霉素和克林霉素双纸片扩散法药敏实验,即D试验,以检测其耐药表型。应用PCR检测大环内酯类-林可酰胺类-链阳菌素B(MLSB)耐药葡萄球菌的3种erm耐药基因,比较耐药表型同基因型的关系。结果D试验结果出现两类不同的诱导耐药阳性表型,分别为D表型和D 表型。克林霉素对8株葡萄球菌的抑菌圈在靠近红霉素一侧变钝的截面平整而清晰,为D表型;其余32株钝形截面边缘到克林霉素纸片之间生长有细小菌落,为D 表型。PCR结果显示D表型的菌株含ermA基因,而D 表型主要含ermC或者同时含有ermA和ermC。两纸片距离10~15mm有利于预测菌株的基因型。结论D试验可有效检测葡萄球菌诱导型克林霉素耐药性,且可预测其诱导耐药的基因型。两类D试验阳性表型同基因型存在相关性。

Two distinct positive phenotypes by D-zone test and genotype analysis in Staphylococcus

Objective To investigate the erythromycin-induced phenotypes and genotypes in clindamycin-resistant Staphylococcus. Methods The double disk diffusion method or D-zone test was used to test the resistance phenotypes of 116 isolates of Staphylococcus aureus or coagulase-negative Staphylococcus. PCR was performed to detect three erm genes in MLSB-resistant Staphylococcus and analyze the relationship between genotype and phenotype. Results The 40 positive isolates by D-zone test yielded two distinct induction phenotypes. The D-zone phenotype of 8 isolates showed a blunted edge but an otherwise clear zone of inhibition around the clindamycin disk, while the D phenotype for the other 32 isolates showed a blunted, D-shaped zone around clindamycin disk near erythromycin disk and small colonies growing to clindamycin disk in otherwise clear zone. PCR results showed that isolates with a D phenotype harbored ermA, isolates with a D phenotype contained either ermC or ermA and ermC. The distance from 10 to 15 mm between clindamycin disk and erythromycin disk could predict induction genotype favorably. Conclusions The double disk diffusion method can not only identify the inducible resistance to clindamycin, but also predict its corresponding genotypes in Staphylococcus. There exists correlation between the two distinct induction phenotypes and the corresponding genotype.