Vancomycin resistant Enterococcus spp. from crows and their environment in metropolitan Washington State, USA: Is there a correlation between VRE positive crows and the environment?
This executive summary was written for the Advanced Technical Communication in Public Health course at the University of Washington.
Roberts et al., 2016 Vancomycin resistant Enterococcus spp. from crows and their environment in metropolitan Washington State, USA: Is there a correlation between VRE positive crows and the environment? Vet Microbiol 2016 Oct 15;194:48-54.
Enterococci are opportunistic pathogens that cause a variety of infections in humans. The danger they pose is increased by several factors: their ability to withstand a range of temperatures, pH, and salinity; their resistance to antibiotics such as vancomycin; and their persistence in the environment, including carriage by animal species. Because birds have been previously linked to environmental contamination and because crows interact extensively with urban areas, Roberts et al. chose crows as an animal model for studying the appearance of vancomycin resistant enterococci (VRE) in wildlife.
In order to identify the relationship between crow VRE and environmental VRE, the researchers collected fecal material from several crow feeding sites: a Seattle area waste water treatment plant (WWTP), four dairy farms, and a restored wetland habitat at UW Bothell. In addition, they collected WWTP treated waste, dairy cow fecal samples, and wetland soil and water. These samples were processed and cultured to identify any VRE isolates. PCR assays then confirmed the presence of vanA, vanB, and vanC1 in each isolate. Any isolate that tested positive for one or more van genes was then speciated using 16S PCR and sequencing and checked for multidrug resistance.
In all, they collected 245 samples, 156 from crows and 89 from the environment. From those, 130 VRE isolates were identified. PCR analysis revealed 38 crow and 49 environmental VRE positive samples. Speciation of 57 of those isolates identified four crow vanA E. faecium, representing 2.7% of the total crows sampled and 10.3% of the characterized crow enterococci; 30 environmental E. faecium, encompassing 78.9% of samples; and vanC1 E. gallinarum in all crows and environmental isolates. The ubiquity of E. gallinarum may indicate a role in normal crow gut microbiota. The four crow E. faecium and a significant portion of the E. gallinarum were also multidrug resistant. Scientists found that the concentration of crow VRE differed by site, likely because of behavioral differences required for inhabiting each. Surprisingly, the variable levels of vanA E. faecium found among crows from different sites did not correlate with environmental levels of those same bacteria at any of the locations.
The work presented here is the first to compare crow VRE to that of their environment and highlights the human health risk of bird-borne disease. One limitation of the study is that crows’ mobility over the course of days and seasons may cause the acquisition of bacteria from distant areas; this may explain the identification of crow VRE that did not match those found in the examined environments and points to a more complex network of contamination. Roberts et al. close by raising two troubling questions: what is the magnitude of the risk birds pose to human health? And conversely, what risk do humans pose to animals as the source of pathogenic bacterial contamination?