Vancomycin-Resistant Enterococci and Bacterial Community Structure following a Sewage Spill into an Aquatic Environment

Abstract

Sewage spills can release antibiotic-resistant bacteria into surface waters, contributing to environmental reservoirs and potentially impacting human health. Vancomycin-resistant enterococci (VRE) are nosocomial pathogens that have been detected in environmental habitats, including soil, water, and beach sands, as well as wildlife feces. However, VRE harboring vanA genes that confer high-level resistance have infrequently been found outside clinical settings in the United States. This study found culturable Enterococcus faecium harboring the vanA gene in water and sediment for up to 3 days after a sewage spill, and the quantitative PCR (qPCR) signal for vanA persisted for an additional week. Culturable levels of enterococci in water exceeded recreational water guidelines for 2 weeks following the spill, declining about five orders of magnitude in sediments and two orders of magnitude in the water column over 6 weeks. Analysis of bacterial taxa via 16S rRNA gene sequencing showed changes in community structure through time following the sewage spill in sediment and water. The spread of opportunistic pathogens harboring high-level vancomycin resistance genes beyond hospitals and into the broader community and associated habitats is a potential threat to public health, requiring further studies that examine the persistence, occurrence, and survival of VRE in different environmental matrices.

Importance: Vancomycin-resistant enterococci (VRE) are harmful bacteria that are resistant to the powerful antibiotic vancomycin, which is used as a last resort against many infections. This study followed the release of VRE in a major sewage spill and their persistence over time. Such events can act as a means of spreading vancomycin-resistant bacteria in the environment, which can eventually impact human health.

FIG 1

Culturable enterococci in water and sediment at site NC-03, near the site of the sewage spill. The dashed line represents the EPA standard for a single-sample maximum of enterococci in recreational water (130 CFU per 100 ml). Letters indicate where VRE were cultured (C) and where vanA was detected within 800 m of the spill (NC-01, NC-02, and NC-03). Note that on 1 October 2014, no sediment was collected or processed (indicated by *).

FIG 2

Analysis of DNA sequencing of the 16S rRNA gene in water and sediment on seven dates at site NC-03. The blue gradient represents water samples, and the red gradient represents sediment samples; the color gradient represents different time points in either water (W) or sediment (S) where darker shades are immediately after the spill or earlier in time.

FIG 3

Relative abundance of select sewage-associated OTUs (Bacteroidaceae, Ruminococcaceae, Lachnospiraceae, Porphyromonadaceae, Veillonellaceae, and Prevotellaceae) at site NC-03 in water and sediment samples.

FIG 4

Dominant families in sediment and water at site NC-03 on all sampling dates.