rpoB유전자를 이용한 Acinetobacter 임상균주의 동정

Abstract

Background: The importance of Acinetobacter is increasing as the serious etiologic agent of nosocomial infection because of their frequent isolation and multidrug resistance. It is necessary to apply molecular biological methods for the identification of Acinetobacter species. because conventional methods has limitation to identify them. The 16S rRNA gene analysis is the one of the most commonly used molecular methods. The differentiation of closely related species of Acinetobacter by 16S rRNA gene analysis is difficult due to high interspecies similarity among them. Recently the rpoB gene analysis is increasingly applied for the identification of various bacteria because of its high discriminatory power. The purpose of this study is to assess the usefulness of the rpoB gene analysis for the identification of Acinetobacter species and to know the distribution of Acinetobacter species in the clinical isolates of a university hospital in Korea. We also compared the results of identification by rpoB gene analysis, 16S rRNA gene analysis, and Vitek 2 system.

Materials and Methods: We tested 95 clinical isolates of Acinetobacter species which were identified as Acinetobacter by Vitek 2 system in Chosun University Hospital. We performed PCR-direct sequencing of rpoB gene and 16S rRNA gene with 95 clinical isolates of Acinetobacter species. The phylogenetic study on them was conducted with DNASTAR program. We compared the distribution of Acinetobacter species in 95 clinical isolates which were determined by rpoB gene analysis, 16S rRNA gene analysis, and Vitek 2 system. We compared antimicrobial resistance rate according to the species of Acinetobacter also.

Results: The identification rates and discriminatory power of rpoB gene analysis were better than those of 16S rRNA gene analysis or Vitek 2 system. The numbers of species identified by rpoB gene analysis, 16S rRNA gene analysis, and Vitek 2 system were seven, six, and four, respectively. The most common Acinetobacter species identified by rpoB gene analysis was A. baumannii(55.8%), followed by A. bereziniae(12.6%), Genomic species 3 (5.3%), Genomic species 16 (4.2%), A. junii/A. grimontii(3.1%), A. calcoaceticus (1.1%), and A. ursingii (1.1%). The results of 16S rRNA gene analysis were similar to those of rpoB gene analysis. However the discriminatory power of the former is lower than the latter. Fifty-two (98.1%) of 53 A. baumannii identified by rpoB gene analysis were identified as A baumannii/Genomic species 13 by 16S rRNA gene analysis. The identification rate of 16S rRNA gene analysis was lower than that of rpoB gene analysis. Because the number of strains which were not identified at species level were 16 (16.8%) by rpoB gene analysis and 33 (34.7%) by 16S rRNA gene analysis. Only 53 (74.6%) of 71 strains identified as A. baumannii by Vitek 2 system was identified as A .baumannii by rpoB gene analysis. Among the remaining 18 strains, 12 strains were not identified at the species level. Comparison of the antimicrobial susceptibility test results of 91 strains of Acinetobacter according to the species of Acinetobacter identified by rpoB gene analysis revealed the difference among species of Acinetobacter. A. baumannii showed more than 70% of high resistance rate on the most antibiotics. On the other hand, the other species of Acinetobacter showed high susceptibility on them.

Conclusion: The rpoB gene analysis is useful for the identification of clinical isolates of Acinetobacter. The results of 16S rRNA gene analysis were relatively similar to those of rpoB gene analysis. However the discriminatory power and identification rate of the former were lower than the latter. There was the difference in the antimicrobial resistance rate among species of Acinetobacter.