Spread of vancomycin-resistant Enterococcus faecium ST133 in the aquatic environment in Switzerland

OBJECTIVES

The global dissemination of vancomycin-resistant enterococci (VRE) has become a serious public-health concern. Although outbreaks are typically caused by nosocomial transmission, contaminated food and water may contribute to the spread of VRE. The aim of this study was to assess the presence of VRE in flowing surface water bodies in Switzerland and to characterise the isolates.

METHODS

Surface water was sampled from rivers, streams and canals throughout Switzerland and was screened for the presence of VRE. Whole-genome sequencing was used to identify antimicrobial resistance genes and the phylogenetic similarity of the obtained isolates.

RESULTS

VRE were detected in 6 (3.1%) of 191 water samples. The six VRE-containing samples were all collected near treated wastewater discharge sites. The six isolates were identified as Enterococcus faecium sequence type 133 (ST133) and harboured the vancomycin resistance-conferring vanA gene cluster on transposon Tn1546. They showed a close phylogenetic relationship to ST133 swine faecal isolates obtained during a previously reported screening in Switzerland.

CONCLUSION

Our results suggest that surface water contributes to the environmental dissemination of VRE. Repeated identification of ST133 clones in geographically distinct water sampling sites and swine faecal samples collected in slaughterhouses may indicate a local dominance of this VRE lineage in Switzerland.

Environmental dissemination of pathogenic Listeria monocytogenes in flowing surface waters in Switzerland

Listeria monocytogenes is an opportunistic pathogen that is widely distributed in the environment. The aquatic environment may represent a potential source for the transmission of L. monocytogenes to animals and the food chain. The present study assessed the occurrence of L. monocytogenes in 191 surface water samples from rivers, streams and inland canals throughout Switzerland. Twenty-five (13%) of the surface water samples contained L. monocytogenes. Whole genome sequence (WGS) data were used to characterize the 25 isolates. The isolates belonged to major lineages I and II, with the majority assigned to either serotype 1/2a (48%), or 4b (44%). The predominant CCs identified were the hypervirulent serotype 4b clones CC1 and CC4, and the serotype CC412; all three have been implicated in listeriosis outbreaks and sporadic cases of human and animal infection worldwide. Two (8%) of the isolates belonged to CC6 which is an emerging hypervirulent clone. All isolates contained intact genes associated with invasion and infection, including inlA/B and prfA. The four CC4 isolates all harbored Listeria pathogenicity island 4 (LIPI-4), which confers hypervirulence. The occurrence of L. monocytogenes in river ecosystems may contribute to the dissemination and introduction of clinically highly relevant strains to the food chain.

Linezolid-resistant Enterococcus faecalis ST16 harbouring optrA on a Tn6674-like element isolated from surface water

OBJECTIVES

The objective of this work was to characterise an optrA-carrying Enterococcus faecalis ST16 isolate recovered from a river water sample in Switzerland.

METHODS

Linezolid-resistant E. faecalis F102 was recovered from surface water in Switzerland and was subjected to comprehensive genotypic characterisation and analysis of the genetic environment of the oxazolidinone/phenicol resistance gene optrA. Whole-genome sequencing (WGS) was performed to detect linezolid resistance mechanisms, including mutations in 23S rRNA and ribosomal protein genes as well as acquired resistance genes. The isolate was further characterised by multilocus sequence typing (MLST) and identification of virulence genes.

RESULTS

WGS detected the presence of optrA identical to the original optrA gene from E. faecalis E349. Analysis of the genetic environment revealed the association of optrA with fexA and a Tn6674-like transposon in co-existence with spc and erm(A) resistance genes. Sequence alignment indicated that the genetic environment of optrA was identical to a Tn6674-like variant from E. faecalis previously isolated from diseased and healthy humans and food-producing animals in the Asia-Pacific region. Enterococcus faecalis F102 did not contain any mutations in 23S rRNA or in genes encoding ribosomal proteins L3, L4 and L22. A total of 14 other resistance genes and 16 virulence genes were detected. Enterococcus faecalis F102 was assigned in silico to ST16.

CONCLUSION

The spread of optrA-carrying E. faecalis ST16 with a high pathogenic potential in surface water is a worrisome aspect from a public-health perspective.

Decontamination of knives used in a slaughterhouse by a commercial non-thermal UV-C treatment

To assess the antimicrobial effect of a commercial UV-C system, knives inoculated with Escherichia coli and Staphylococcus aureus as well as naturally contaminated and collected from the wet and clean area of a slaughterhouse knives were examined. For inoculated knives, UVC treatment for 30 s reduced mean E. coli counts by 5.1 log CFU cm-2 and mean S. aureus counts by 4.5 log CFU cm-2. The presence of blood lowered mean reductions to 3.4 log CFU cm-2 for E. coli and to 2.5 log CFU cm-2 for S. aureus. The presence of fat had a greater negative impact on the efficacy of the UV-C treatment resulting in mean reductions <1.8 log CFU cm-2. For naturally contaminated knives from a slaughterhouse, total viable counts (TVC) before UV-C treatment varied considerably (wet area: 2.0-6.0 log CFU cm-2, clean area: 1.0-3.0 log CFU cm-2). UV-C treatment for 30s reduced mean TVC by 0.8 log CFU cm-2 (wet area) and 0.6 log CFU cm-2 (clean area), but the effect varied greatly between individual knives. Thus, under commercial conditions, the antibacterial effect of UV-C for the decontamination of knives is affected by the presence of additional contaminations like blood or fat. The adequate cleaning of the knives prior to UV-C decontamination is therefore of central importance.