Background: The increasing demand for agricultural water requires identification and safety assessment of alternative water sources, as pathogenic bacteria in the water could cause health risks if transferred to growing produce. Some species of Enterococcus, an opportunistic pathogen and water quality indicator, exhibit antimicrobial resistance and can transfer resistance traits to other bacterial taxa, including human pathogens. Thus, it is important to consider antimicrobial resistance when assessing the safety of irrigation water for food crops.
Goal: The goal of this project is to evaluate the distribution and antimicrobial resistance of Enterococcus faecalis and E. faecium in surface and recycled wastewaters in the Mid-Atlantic region of the U.S.
Objectives: 1) Identify E. faecalis and E. faecium in enterococci isolate collection, recovered from surface and recycled wastewater samples from a variety of sites in the Mid-Atlantic. 2) Evaluate susceptibilities of E. faecalis and E. faecium isolates to a suite of antimicrobials. 3) Assess whether antimicrobial resistance in E. faecalis and E. faecium is associated with season, water type, temperature, pH and salinity.
Approach: Enterococcus species isolated from surface and recycled water samples collected between October 2016 and September 2017 have been archived in -80°C storage. To identify E. faecalis and E. faecium in the collection, PCR amplification targeting the species-specific ddl (D-Ala:D-Ala ligase) gene of two Enterococcus species, E. faecalis and E. faecium is being conducted on these isolates. Once the E. faecalis and E. faecium isolates are identified, antimicrobial susceptibility testing will be conducted to evaluate their susceptibility to a suite of antimicrobials, including ampicillin, ceftriaxone, ciprofloxacin, clindamycin, daptomycin, erythromycin, gatifloxacin, gentamicin, levofloxacin, linezolid, oxacillin + 2% NaCl, penicillin, quinupristin/dalfopristin, rifampicin, streptomycin, tetracycline, trimethoprim/sulfamethoxazole, and vancomycin, using the microbroth dilution method.
Results: A total of 447 enterococci isolates from four water sources (reclaimed wastewater, non-tidal river, tidal river, pond) will be identified by species (E. faecalis, E. faecium, or other). Logistic regression will be used to evaluate correlation of antimicrobial resistance with season, water type, temperature, pH, and salinity.
Importance to public health: Understanding antimicrobial resistance in irrigation water and reducing risk to public health is critical in light of the shrinking treatment options for infectious diseases caused by antimicrobial resistant pathogens.