Researchers have isolated pathogenic, drug-resistant bacteria from wastewater treatment facilities in the UK.
Drug-resistant bacteria are increasingly a public health concern as they can lead to serious illness or death, especially among people with compromised immune systems. While drug-resistant Enterococcus faecium are known to circulate in hospitals, their environmental abundance has been unclear.
A team led by Cambridge University researchers collected samples from 20 municipal wastewater plants in England, finding drug-resistant E. faecium at all the locations in untreated waste. As they reported in Genome Research this week, the researchers compared the genomes of bacteria they collected to uncover two major lineages, one of which included not only E. faecium resistant to vancomycin, but also to other drugs.
“We conclude that our findings are consistent with widespread distribution of hospital-adapted [vancomycin-resistant E. faecium] beyond acute healthcare settings with extensive release of VREfm into the environment in the East of England,” senior author Sharon Peacock, a clinical microbiologist at Cambridge, and her colleagues wrote in their paper.
The researchers collected both treated and untreated wastewater samples between June 2014 and January 2015 from 20 municipal plants in the East of England. Half the plants received waste directly from hospitals and half did not.
All the untreated samples from all plants harboured both ampicillin- and vancomycin-resistant E. faecium, the researchers reported. Treatment, though, reduced the number of enterococci present, especially treatment with ultraviolet light. Treated wastewater samples from the three plants using UV decontamination had the greatest reduction, with no detected ampicillin- or vancomycin-resistant E. faecium in those samples.
The researchers also collected four samples from a hospital sewer between September 2014 and December 2015, finding ampicillin- and vancomycin-resistant E. faecium in all samples.
Sequencing of 423 E. faecium isolates — 383 from wastewater treatment plants and 40 from the hospital sewer — and in silico MLST analysis uncovered 93 sequence types, 28 of which were novel, a finding the researchers said indicated high genetic diversity.
Through a phylogenetic analysis based on the genomes of these 423 E. faecium isolates as well as 187 E. faecium isolates associated with bloodstream infections in patients in the region and 10 publicly available E. faecium genomes, the researchers uncovered two main lineages, clade A and clade B. Clade A, they noted, could be further broken down into clades A1 and A2.
Clades A2 and B included ampicillin-susceptible E. faecium, the researchers noted. Clades A1 and A2 included ampicillin-resistant E. faecium, while only clade A1 contained vancomycin-resistant E. faecium.
The 481 isolates belonging to clade A1, the researchers noted, hailed from wastewater treatment plants, hospital sewage, and bloodstream isolates. The largest cluster included 72 isolates from each of those locales that share a common ancestor that lived slightly more than nine years ago.
Within these clade A1 isolates, the researchers uncovered 28 different resistance genes, including spw, cat_pC221, tet40, and cueO that provide resistance to spectinomycin, chloramphenicol, tetracycline, and copper, respectively.
These findings of resistant bacteria even among treated sewage, the researchers said, indicate that stronger controls are needed. “Ultraviolet light was used at three study plants and was effective in decontaminating wastewater prior to release,” they noted. “This represents a ready solution that would reduce environmental contamination with VREfm and drug-resistant bacteria more generally.”