Abstract
Multilocus variable number tandem repeat analysis (MLVA) is a subtyping technique for characterizing human pathogenic bacteria such as enterohemorrhagic Escherichia coli (EHEC) O157. We determined the phylogeny of 202 epidemiologically unrelated EHEC O157:H7/H- clinical isolates through 8 MLVA loci obtained in Germany during 1987-2008. Biodiversity in the loci ranged from 0.66 to 0.90. Four of 8 loci showed null alleles and a frequency < or =44.1%. These loci were distributed among 48.5% of all strains. Overall, 141 MLVA profiles were identified. Phylogenetic analysis assigned 67.3% of the strains to 19 MLVA clusters. Specific MLVA profiles with an evolutionary persistence were identified, particularly within sorbitol-fermenting EHEC O157:H-.These pathogens belonged to the same MLVA cluster. Our findings indicate successful persistence of this clone.
Highlights
Enterohemorrhagic Escherichia coli (EHEC) O157:H7 infections have substantial medical, public health, and economic effects [1,2]
To identify reservoirs of EHEC O157:H7 infections and of other foodborne pathogens and to elucidate the molecular epidemiology of these pathogens in the United States, PulseNet was established in 1996 [6]. This US national molecular subtyping network for foodborne disease surveillance facilitates subtyping of bacterial foodborne pathogens for epidemiologic purposes. This network is based on characterization of whole bacterial genomes by using macrorestriction digestion patterns that are separated by pulsed-field gel electrophoresis (PFGE), a technique that has emerged as a common standard for subtyping EHEC O157 isolates [6]
We investigated the phylogeny of EHEC O157:H7 and SF EHEC O157:H– strains isolated during 1987–2008 in Germany by applying the current PulseNet MLVA protocol for E. coli O157 [23]
Summary
Enterohemorrhagic Escherichia coli (EHEC) O157:H7 infections have substantial medical, public health, and economic effects [1,2]. Band patterns can be altered by the presence of mobile genetic elements To overcome these drawbacks, other molecular methods were developed, among them multilocus variable number tandem repeat (VNTR) analysis (MLVA). For EHEC O157, different MLVA schemes with some overlaps of VNTR regions have been published and have demonstrated a capability to detect outbreaks and differentiate closely related EHEC O157 isolates not discriminated by PFGE [8,14,15]. These findings qualify MLVA as the second-generation subtyping method for PulseNet [8]
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