Sakar Havva, Mumcuoğlu Ipek, Aksu Neriman, Karahan Zeynep Ceren, Kurşun Senol, Kuştimur Semra
Ankara Numune Training and Research Hospital, Department of Medical Microbiology, Ankara, Turkey.
Mikrobiyol Bul. 2012 Apr;46(2):170-9.
Macrolide-lincosamide-streptogramin B (MLSB) group antibiotics are recommended as first choice in the treatment of staphylococcal infections. All of those drugs bind to the 50S subunit of bacterial ribosomes, thus cross-resistance is a major concern in this group of drugs. The mechanisms associated to resistance are (a) ribosomal methylation due to the methylases encoded by erm genes, (b) active drug efflux due to msrA, msrB, vga, vgb gene activity, (c) enzymatic inactivation of the drug due to the activity of linA, vat, vatB genes. While the most common resistance genes are ermA, ermB, ermC, msrA and msrB genes; linA, vga, vgb, vat and vatB genes have also been found in some studies. In this study it was aimed to investigate the presence of the rare MLSB resistance genes and their coexistence with erm and msr genes in 454 clinical isolates of coagulase-negative staphylococci (CNS). Of them 46.5% (n= 211) were S.hominis, 30.8% (n= 140) were S.epidermidis, 12.1% (n= 55) were S.haemolyticus, 3.5% (n= 16) were S.warnerii and 7% (n= 32) were the other coagulase-negative staphylococcal species. Resistance phenotypes were determined by using D-test method according to the recommendation of Clinical and Laboratory Standards Institute (CLSI). With the D-test 107 (23.6%) strains were determined as M phenotype (resistant to erythromycin and inducible clindamycin resistance was not detected), 92 (20.3%) were iMLSB phenotype (inducible clindamycin resistance was detected by the D-test) and 110 (24.2%) were cMLSB phenotype (constitutive erythromycin and clindamycin resistance was detected). linA, vga, vgb, vat, vatB, ermA, ermB, ermC, msrA, msrB genes were investigated by polymerase chain reaction in all strains showing iMLSB (n= 92) and cMLSB (n= 110) phenotypes and 46 randomly selected strains among 107 strains exhibiting the M phenotype. linA gene was found in 91 (20%) strains as single gene or in combination with erm or msr genes, and vga gene was found in 19 (4.2%) strains. linA gene was found in 52% of iMLSB phenotype, in 26% of cMLSB phenotype and 13% of M phenotype while vga gene was found in 5.4% of iMLSB phenotype, in 12% of cMLSB phenotype and in 0.9% of M phenotype. The most common resistance gene among iMLSB and cMLSB phenotypes was ermC (32.6% and 42.7%, respectively), followed by ermC + linA gene combination (31.5% and 14.5%, respectively). The most frequent gene combination was msrA and msrB in M phenotype (34.8%) and it was followed by a combination of msrA + msrB + linA genes (19.1%). None of the strains revealed presence of vgb, vat and vatB genes. There were no previous reports about the rarely detected resistance genes against MLSB antibiotics in our country. This was the first study which reported the frequency of linA, vga, vgb, vat and vatB genes in MLSB resistant CNS. In conclusion, since linA and vga genes were detected in high frequency in MLSB resistant CNS in this study, it was thought that the investigation of these genes should be included in the further related epidemiologic gene research.
大环内酯-林可酰胺-链阳菌素B（MLSB）类抗生素被推荐作为治疗葡萄球菌感染的首选药物。所有这些药物都与细菌核糖体的50S亚基结合，因此交叉耐药是这类药物的一个主要问题。与耐药相关的机制有：（a）由erm基因编码的甲基化酶导致核糖体甲基化；（b）msrA、msrB、vga、vgb基因活性导致药物主动外排；（c）linA、vat、vatB基因活性导致药物酶失活。最常见的耐药基因是ermA、ermB、ermC、msrA和msrB基因；在一些研究中也发现了linA、vga、vgb、vat和vatB基因。本研究旨在调查454株凝固酶阴性葡萄球菌（CNS）临床分离株中罕见的MLSB耐药基因的存在情况及其与erm和msr基因的共存情况。其中，人葡萄球菌占46.5%（n = 211），表皮葡萄球菌占30.8%（n = 140），溶血葡萄球菌占12.1%（n = 55），沃氏葡萄球菌占3.5%（n = 16），其他凝固酶阴性葡萄球菌占7%（n = 32）。根据临床和实验室标准协会（CLSI）的建议，采用D试验法确定耐药表型。通过D试验，107株（23.6%）菌株被确定为M表型（对红霉素耐药且未检测到诱导型克林霉素耐药），92株（20.3%）为iMLSB表型（通过D试验检测到诱导型克林霉素耐药），110株（24.2%）为cMLSB表型（检测到组成型红霉素和克林霉素耐药）。对所有表现出iMLSB（n = 92）和cMLSB（n = 110）表型的菌株以及107株表现出M表型的菌株中随机选择的46株进行聚合酶链反应，检测linA、vga、vgb、vat、vatB、ermA、ermB、ermC、msrA、msrB基因。发现91株（20%）菌株中存在linA基因，其为单基因或与erm或msr基因组合存在，19株（4.2%）菌株中存在vga基因。linA基因在iMLSB表型菌株中占52%，在cMLSB表型菌株中占26%，在M表型菌株中占13%；而vga基因在iMLSB表型菌株中占5.4%，在cMLSB表型菌株中占12%，在M表型菌株中占0.9%。iMLSB和cMLSB表型中最常见的耐药基因是ermC（分别为32.6%和42.7%），其次是ermC + linA基因组合（分别为31.5%和14.5%）。M表型中最常见的基因组合是msrA和msrB（34.8%），其次是msrA + msrB + linA基因组合（19.1%）。所有菌株均未检测到vgb、vat和vatB基因。我国此前尚无关于MLSB抗生素罕见耐药基因的报道。这是首次报道MLSB耐药CNS中linA、vga、vgb、vat和vatB基因频率的研究。总之，由于本研究中在MLSB耐药CNS中高频检测到linA和vga基因，因此认为在进一步的相关流行病学基因研究中应纳入对这些基因的调查。
