Unusual form of oxacillin resistance in methicillin-resistant Staphylococcus aureus clinical strains
Unusual form of oxacillin resistance in methicillin-resistant Staphylococcus aureus clinical strains
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DOI：
10.1016/j.diagmicrobio.2008.04.003
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发表时间：
2008-08-01
影响因子：
2.9
通讯作者：
Rosato, Adriana E.
中科院分区：
文献类型：
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作者：
Forbes, Betty A.;Bombicino, Karina;Rosato, Adriana E.
对苯唑西林耐药在单个菌株群体中存在差异表达的机制仍未完全了解。本研究通过对832株金黄色葡萄球菌的连续筛选，获得25株耐甲氧西林金黄色葡萄球菌(MRSA)对苯唑西林敏感的mecA阳性菌株。将24 h的苯唑西林琼脂平板延伸至48 h(即GOA48-MRSA)，对这25株(占调查菌株总数的3%)进行了统一检测。22株青霉素结合蛋白2a检测呈阳性，其余3株mecA不一致阳性。用mecA探针进行菌落杂交(80%的菌落与mecA探针杂交较差)，对上述3株菌的mecA检测结果不一致进行了研究。在苯唑西林暴露前，扩增空的SCCmec插入位点(AttB)的PCR产物在所有3个分离株中都呈阳性，而整合的成分仅在苯唑西林生长的分离株中呈阳性。其余22株菌株未发现mecA基因被切除，显示mecA稳定。我们得出结论，在对苯唑西林敏感的MRSA阳性mecA菌株中，对β-内酰胺类药物的耐药性与极端异质性表达的耐药性有关，在某些情况下，结合苯唑西林SCCmec切除。(C)2008 Elsevier Inc.保留所有权利。
The mechanisms by which there is differential expression of resistance to oxacillin within the populations of a single strain remains to be fully understood. The purpose of this study was to evaluate and characterize 25 GOA48 methicillin-resistant Staphylococcus aureus (MRSA) oxacillin-susceptible mecA-positive strains, which were obtained by screening consecutively 832 S. aureus isolates. These 25 isolates (3% of the total strains investigated) were uniformly detected by extending the 24-h oxacillin agar screen plate to 48 h (namely, GOA48-MRSA). Twenty-two isolates tested positive for penicillin-binding protein 2a, whereas the remaining 3 isolates were inconsistently mecA positive. Inconsistent detection of mecA by polymerase chain reaction (PCR) in the mentioned 3 isolates was investigated by colony hybridization using a mecA probe (80% of colonies hybridized poorly to the probe). A PCR product that amplified the empty SCCmec insertion site (attB), present only if the element was excised, resulted positive in all 3 isolates before oxacillin exposure, whereas integrated elements were positive only for oxacillin-grown isolates. The remaining 22 strains did not reveal excision demonstrating stable mecA. We concluded that resistance to beta-lactams in MRSA-positive mecA strains susceptible to oxacillin is associated to an extreme heterogeneous expression of resistance combined in some cases to oxacillin SCCmec excision. (c) 2008 Elsevier Inc. All rights reserved.