Abstract
BackgroundEnterococci are now well recognised for their ability to transfer antibiotic resistance and for their association with nosocomial infections, but less is known regarding their relevance in the wider environment. Enterococcus faecalis and Enterococcus faecium were isolated from a range of agrarian associated sources (low-flow water, septic tank, poultry litter, high flow water, slurry/soil) and were assessed for latent ability to transfer antimicrobial resistance.ResultsThe isolates were tested for phenotypic clumping in the presence of cell-free supernatant from other isolates. Some isolates were identified which demonstrated clumping, indicating that they possessed peptide sex pheromone conjugal machinery. All isolates were also tested for antibiotic resistance phenotypes using both disc diffusion and minimum inhibitory concentration (MIC) assays. These tests revealed that the enterococci demonstrated both phenotypic clumping and antibiotic resistance phenotypes. Based on these selection criteria, the isolates were identified as having the potential for horizontal gene transfer and were used to investigate the transfer of multiple antibiotic resistance phenotypes. Conjugal transfer of antibiotic resistance phenotypes was determined using a solid agar mating method followed by a standard antibiotic selection test resulting in different transfer patterns. An interspecies conjugal transfer of vancomycin resistance from E. faecalis to E. faecium was identified while the remaining reactions were within the same species. Transfer efficiencies ranging from 2 × 10−1 to 2.3 × 10−5 were determined based on the reactions of three donor isolates (MF06036, MF0410 and MF06035) and two recipient isolates (MW01105Rif and ST01109Rif), with the transfer of vancomycin, erythromycin and tetracycline resistance genes.ConclusionsThe conjugation reactions and selection conditions used in this study resulted in a variety of co-transferred resistance phenotypes suggesting the presence of different mobile elements in the set of natural isolates. This study highlights the potential for extensive horizontal gene transfer in a previously neglected reservoir for enterococci.
Highlights
Enterococci are well recognised for their ability to transfer antibiotic resistance and for their association with nosocomial infections, but less is known regarding their relevance in the wider environment
Bacterial strains and reagents The E. faecalis and E. faecium used in this study (Table 1), were previously isolated from various sources feeding into river headwaters [14]
The enterococci recovered from a variety of agrarian sources (Table 1) were tested for antibiotic resistance phenotypes as well as their pheromone-induced clumping ability, to identify a subgroup of isolates that were likely to undergo horizontal gene transfer by conjugation
Summary
Enterococci are well recognised for their ability to transfer antibiotic resistance and for their association with nosocomial infections, but less is known regarding their relevance in the wider environment. Enterococci are Gram positive, facultative anaerobes and despite not forming spores they are tolerant to a range of environmental conditions [1]. They are ubiquitous inhabitants of the mammalian gastrointestinal tract and are regularly recovered from agrarian ecosystems [2, 3]. They do not thrive in water they have been found in surface waters prone to faecal contamination [4] and because of their resistance to salinity they pose a threat to recreational bathing waters [5, 6]. Water catchments close to farmland have the potential to provide a reservoir of antibiotic resistant enterococci which may pose a threat to human health
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
