Abstract
BackgroundMLVA (multiple-locus variable-number tandem repeat analysis) is a reliable typing technique introduced recently to differentiate also isolates of Enterococcus faecium. We used the established VNTR (variable number of tandem repeats) scheme to test its suitability to differentiate 58 E. faecium isolates representing mainly outbreaks and clusters of infections and colonizations among patients from 31 German hospitals. All isolates were vancomycin-resistant (vanA type). Typing results for MLVA are compared with results of macrorestriction analysis in PFGE (pulsed-field gel electrophoresis) and MLST (multi-locus sequence typing).ResultsAll 51 but one hospital isolates from 1996–2006 were assigned to the clonal complex (CC) of epidemic-virulent, hospital-adapted lineages (MLST CC-17; MLVA CC-1) and differed from isolates of sporadic infections and colonizations (n = 7; 1991–1995) and other non-hospital origins (n = 27). Typing of all 58 hospital VRE revealed MLVA as the least discriminatory method (Simpson's diversity index 0.847) when compared to MLST (0.911) and PFGE (0.976). The two most common MLVA types MT-1 (n = 16) and MT-159 (n = 14) combined isolates of several MLST types including also major epidemic, hospital-adapted, clonal types (MT-1: ST-17, ST-18, ST-280, ST-282; MT-159: ST-78, ST-192, ST-203). These data clearly indicate that non-related E. faecium could possess an identical MLVA type being especially critical when MLVA is used to elucidate supposed outbreaks with E. faecium within a single or among different hospitals. Stability of a given MLVA profile MT-12 (ST-117) during an outbreak over a period of five years was also shown.ConclusionMLVA is a suitable method to assign isolates of E. faecium into distinct clonal complexes. To investigate outbreaks the current MLVA typing scheme for E. faecium does not discriminate enough and cannot be recommended as a standard superior to PFGE.
Highlights
multiple-locus variablenumber tandem repeat analysis (MLVA) is a reliable typing technique introduced recently to differentiate isolates of Enterococcus faecium
The selected variable number of tandem repeats (VNTR) were different between the two species, the overall conclusion would suggest MLVA as a typing method on one hand to discriminate highly enough between strains and on the other hand indicate the possibility to establish rather broad phylogenetic relatednesses. To support this hypotheses and to test the applicability of the established MLVA scheme for E. faecium to indicate and differentiate hospital-adapted clonal types appearing in increasing numbers among hospital patients worldwide [16], we investigated hospital isolates representing outbreaks and clusters of infections and colonizations from German hospital patients from the last 15 years using MLVA, SmaImacrorestriction analysis in pulsed-field gel electrophoresis (PFGE), and Multi-locus sequence typing (MLST)
Results of MLST partly confirm cluster assignments based on PFGE data, whereas our data did not show a visible concordance between MLVA and PFGE (Fig. 1)
Summary
MLVA (multiple-locus variable-number tandem repeat analysis) is a reliable typing technique introduced recently to differentiate isolates of Enterococcus faecium. A new method was introduced using small repetitive elements appearing in a variable number and distributed among the genome of a given species. This technique based on a variable number of tandem repeats (VNTR) was named multiple-locus variablenumber tandem repeat analysis (MLVA; [8]). MLVA was established to differentiate high-risk pathogens such as Bacillus anthracis and Francisella tularensis [9,10,11] but has been extended to a numerous number of other bacterial species and scientific questions [8,12] including outbreak investigations for pathogenic bacteria [4,13]
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