Penn Christopher, Moddrell Carol, Tickler Isabella A, Henthorne Mary Ann, Kehrli Megan, Goering Richard V, Tenover Fred C
Lawrence Memorial Hospital, Lawrence, KS 66044, United States.
Cepheid, 904 Caribbean Drive, Sunnyvale, CA 94089, United States.
J Glob Antimicrob Resist. 2013 Jun;1(2):79-83. doi: 10.1016/j.jgar.2013.03.009. Epub 2013 May 1.
Detection of meticillin resistance in Staphylococcus aureus isolates continues to be a challenge. Clinical specimens obtained from abscesses from two epidemiologically unrelated outpatients were positive for meticillin-resistant S. aureus (MRSA) by a commercial PCR assay, but colonies obtained by culture were susceptible to oxacillin by an automated testing method. The colonies were also negative using a penicillin-binding protein 2a (PBP2a) latex agglutination test. Because of the discrepancy between the genotypic and phenotypic results, both isolates were re-tested by PCR, disc diffusion, VITEK 2 and MicroScan and were plated on chromogenic agar. Both isolates also underwent cefoxitin induction for additional susceptibility testing studies. Following overnight induction with cefoxitin, both isolates demonstrated resistance to oxacillin and cefoxitin by the two automated methods and by disc diffusion, and were positive using PBP2a latex agglutination tests. Population analysis failed to identify heteroresistant subpopulations in uninduced isolates. Identifying the presence of MRSA by PCR directly in the specimens was critical for determining the appropriate course of antimicrobial therapy for the patients. Both infections resolved with non-β-lactam therapy.
检测金黄色葡萄球菌分离株中的耐甲氧西林情况仍然是一项挑战。通过商业PCR检测，从两名流行病学上无关联的门诊患者脓肿中获取的临床标本对耐甲氧西林金黄色葡萄球菌（MRSA）呈阳性，但通过自动化检测方法，培养获得的菌落对苯唑西林敏感。使用青霉素结合蛋白2a（PBP2a）乳胶凝集试验，菌落结果也为阴性。由于基因型和表型结果存在差异，对这两个分离株均通过PCR、纸片扩散法、VITEK 2和MicroScan重新检测，并接种于显色琼脂平板上。这两个分离株还进行了头孢西丁诱导以进行额外的药敏试验研究。用头孢西丁过夜诱导后，通过两种自动化方法和纸片扩散法，这两个分离株均显示对苯唑西林和头孢西丁耐药，并且使用PBP2a乳胶凝集试验结果为阳性。群体分析未能在未诱导的分离株中鉴定出异质性耐药亚群。直接在标本中通过PCR鉴定MRSA的存在对于确定患者合适的抗菌治疗方案至关重要。两种感染均通过非β-内酰胺类治疗得以治愈。
