Comparison of Multilocus sequence typing change patterns of Vancomycin resistant Enterococcus faecium in the past nine years
Background : To understand the spread of Vancomycin Resistant Enterococcus (VRE) is an important component of hospital infection control measures. Multilocus sequence typing (MLST) is useful in determining the long–term evolutionary process and minimizes differences in experimental results across individuals and laboratories. It is also useful in determining evolutionary origins and backgrounds of bacterial species. This study carries out MLST analysis on vanA Vancomycin resistant Enterococcus faecium isolated from patient specimen in a single university hospital in the past nine years in order to observe changes in genetic evolution over time.
Method : During the years from 2007 to 2015, 45 clinical isolates of vanA-containing E. faecium were collected from Ajou university hospital in Korea. Species were identified through the VitekII system (BioMerieux, Hazelwood, MO) and antibiotic susceptibility testing was performed by disk diffusion and E-test according to Clinical and Laboratory Standards Institute (CLSI) guidelines. To determine genetic relatedness, Matrix Assisted Laser Desorption Ionization-Time Of Flight mass spectrometry (MALDI-TOF MS) was employed. The multilocus sequence types (MLST) were determined to characterize the clonal diversity of the vanA Vancomycin resistant Enterococcus faecium isolates.
Result : All isolates were highly resistant to ampicillin, teicoplanin, ciprofloxacin, and vancomycin whereas they were most susceptible to linezolid and quinupristin- dalfopristin. 45 clinical isolates were genetically unrelated according to MALDI-TOF MS analysis. MLST showed that the clinical isolates had 7 sequence types (ST), ST17(n=19) being the most common, followed by ST78(n=13), ST192(n=6), ST64(n=4), ST262(n=1), ST414(n=1) and ST981(n=1).
Conclusion : The MLST analysis showed that the sequence types of most isolates belonged to clonal complex 17(CC17). This is consistent with outbreaks in hospitals. The study found that the most common type of separation was changed from ST78 to ST17. We had single observations for ST262, ST414 and ST981 but they appear to be random occurrences. MLST can be useful for speculating the genetic evolution of vanA containing E. faecium isolates.
