Annals of Laboratory Medicine

Korean Society for Laboratory Medicine (대한진단검사의학회)
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Detection of mecA in Strains with Oxacillin and Cefoxitin Disk Tests for Detection of Methicillin-resistant Staphylococcus

Methicillin 내성 Staphylococcus 검출을 위한 Cefoxitin과 Oxacillin 디스크 시험법에서 불일치를 보인 균주에서의 mecA 유전자 검출

Lee, Yang-Soon;Kim, Chang-Ki;Kim, Myung-Sook;Yong, Dong-Eun;Chong, Yun-Sop;Lee, Kyung-Won
이양순;김창기;김명숙;용동은;정윤섭;이경원

  • Published : 2007.08.31
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Abstract

Background : Cinical and Laboratory Standards Institute (CLSI) recommends the use of cefoxitin disks instead of long-used oxacillin disks for screening methicillin-resistant isolates of staphylococci. The frequency of discrepant results and accuracy of the tests were evaluated by detecting mecA gene. Methods : A total of 3,123 Stapylococci isolates from patients in Severance Hospital were tested during September 2005 to August 2006 by the CLSI-recommended test using both cefoxitin and oxacillin disks. The mecA gene was detected by PCR and the oxacillin minimum inhibitory concentration (MIC) was determined by using agar dilution method for the isolates with discrepant tests. Results : Among 1,915 S. aureus islolates tested, one isolate was resistant to oxacillin disk but susceptible to cefoxitin disk; the isolate did not have mecA gene. Another isolate susceptible to oxacillin but resistant to cefoxitin had mecA gene. Among 1,208 coagulase-negative staphylococcal isolates, 15 isolates were resistant to oxacillin disk but susceptible to cefoxitin disk; the isolates did not have mecA genes. Two isolates susceptible to oxacillin disk but resistant to cefoxitin disk had mecA genes. Among the 16 Staphylococcus isolates that did not have mecA gene, 15 isolates had the oxacillin MICs of ≤2 μg/mL and were considered as methicillin-susceptible, while 1 isolate with the MIC of 4 μg/mL was considered as methicillin-resistant. Conclusions : Overall, 1.9% of staphylococcal isolates showed discrepant results when the screening tests were performed by using oxacillin and cefoxitin disks. None of the isolates resistant to oxacillin disk but susceptible to cefoxitin disk had mecA gene. In conclusion, the cefoxitin disk test is more reliable than oxacillin disk test in screening methicillin-resistant staphylococcal isolates.

배경 : Clinical and Laboratory Standards Institute (CLSI)는 methicillin 내성 Staphylococcus의 검출을 위해서는 oxacillin 보다는 cefoxitin 디스크 사용을 권장하고 있다. 본 연구에서는 두 디스크에 의한 methicillin 내성 검출 시험법 간에 불일치를 보이는 빈도를 알아보고 mecA 유전자 검사를 시행함으로서 두 디스크 확산법의 결과를 비교 평가하였다. 방법 : 2005년 9월부터 2006년 8월까지 임상검체에서 분리된 Staphylococcus 3,123주(중복분리주 제외)를 대상으로 하였다. Methicillin 내성은 oxacillin과 cefoxitin 디스크를 이용하여 CLSI 디스크 확산법으로 시험하였다. 두 시험결과가 불일치를 보인 균주에 대해서는 mecA 유전자 PCR과 oxacillin 최저억제농도를 시험하였다. 결과 : S. aureus 1,915주 중에 oxacillin에 내성, cefoxitin에 감수성이었던 1주는 mecA 유전자 음성이었고, oxacillin에 감수성, cefoxitin에 내성이었던 다른 1주는 mecA 유전자 양성이었다. Coagulase-negative Staphylococcas 1,208주 중에 oxacillin에 내성, cefoxitin에 감수성인 15주는 mecA 유전자 음성이었다. 반면 2주는 oxacillin에 감수성, cefoxitin에 내성이었고, mecA 유전자 양성이었다. mecA 유전자 음성인 16주 중에 15주는 oxacillin 최저억제농도가 2 μg/mL 이하로 methicillin 감수성으로, 나머지 1주는 4 μg/mL로 methicillin 내성으로 판정되었다. 결론 : Methcillin 내성 Staphylococcus 검출에 있어서 oxacillin 과 cefoxitin 디스크 시험 결과의 불일치율은 1.9%로 추정되었다. Oxacillin에 내성이고 cefoxitin에 감수성인 균주 중에 mecA 유전자 양성인 균주는 없었으며, cefoxitin 디스크 시험법이 더 정확하다고 판단되었다.

Keywords

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