Effects of season and water type on the distribution and antimicrobial resistance of Enterococcus faecalis and Ent. faecium from surface and reclaimed water

Abstract

Aims: To evaluate the safety of irrigation water sources based on phenotypic antimicrobial resistance (AMR) in Enterococcus spp., a potential environmental reservoir for AMR determinants. Methods and Results: Eleven sites representing fresh and brackish water rivers, ponds and reclaimed water, were sampled over 2 years. Samples (n = 333) yielded 198 unique isolates of Ent. faecalis and Ent. faecium which were tested for antimicrobial susceptibility by microbroth dilution. Species distribution was influenced by water type and season. Enterococcus faecalis was more likely found in freshwater rivers and in summer, and Ent. faecium in reclaimed water and in spring. Only 11% of isolates were pansusceptible, while 48.5% and 26.3% were single (SDR) and multidrug resistant (MDR), respectively. MDR was more likely detected in Ent. faecium than Ent. faecalis. Winter isolates were more likely than summer isolates to exhibit MDR than SDR. Conclusions: Enterococcus faecalis and Ent. faecium in surface and reclaimed water exhibited diverse phenotypic AMR and a low-level resistance to clinically important antimicrobials such as ampicillin, vancomycin and linezolid. Significance and Impact of the Study: Single and multidrug resistance in E. faecalis and E. faecium varied by season but not water type. Antimicrobial resistance prevalence can assist decisions on the safety of irrigation water sources for fresh produce crops.