Escherichia coli antimicrobial resistance variability in water runoff and soil from a remnant native prairie, an improved pasture, and a cultivated agricultural watershed

Authors: MUKHERJEE, MAITREYEE - Texas A&M University; GENTRY, TERRY - Texas A&M University; MJELDE, HEIDI - Texas A&M University; Brooks, John; Harmel, Daren; GREGORY, LUCAS - Texas Water Resources Institute; WAGNER, KEVIN - Oklahoma State University

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2020
Publication Date: 4/28/2020
Citation: Mukherjee, M., Gentry, T., Mjelde, H., Brooks, J.P., Harmel, R.D., Gregory, L., Wagner, K. 2020. Escherichia coli antimicrobial resistance variability in water runoff and soil from a remnant native prairie, an improved pasture, and a cultivated agricultural watershed. Water. 12(5):1251. https://doi.org/10.3390/w12051251.
DOI: https://doi.org/10.3390/w12051251

Interpretive Summary: Antibiotic resistance is a problem that requires understanding of potential sources of resistance in the environment to properly gauge where antibiotic resistance contributions are coming from. Three watersheds in Texas were investigated with varying land use profiles, including managed hay pasture, native prairie, and cropland. Runoff and soil cores were collected from these watersheds to ascertain the release of bacteria from these environmental sources. Isolates were characterized for antibiotic resistance using plate-based discs impregnated with common antibiotics tested against E. coli. The majority of resistance was related to cephalothin resistance over any other antibiotic. Overall 95% of isolates were resistant to at least 1 antibiotic, with resistance spread amongst cephalothin, tetracycline, and ampicillin. The resistance patterns suggest multiple sources of antibiotic resistant E. coli within the environment.

Technical Abstract: Although many previous studies have focused on determining the patterns of antibiotic resistance and multidrug resistance from domestic animals and farm environments, very little is known about the environmental and natural reservoirs of antibiotic and multidrug resistance and the impact of agricultural activities on this. In this study, we collected stormwater runoff and soil samples (5 cm depth) from three watersheds in Texas with varying land uses including managed hay pasture, native prairie, and cropland. E. coli was isolated and enumerated from each of these sites using EPA method 1603. Isolates were analyzed for patterns of antibiotic resistance by antimicrobial sensitivity testing using the Kirby-Bauer disk-diffusion method for tetracycline, imipenem, cephalothin, gentamycin, sulfamethoxazole, cefoperazone and ampicillin. In general, a higher rate of antibiotic resistance was observed in the water E.coli isolates compared to the soil isolates. Overall, more isolates were resistant to the antibiotic cephalothin than any of the other antibiotics. Of the tested E. coli isolates from the water samples, 95% were resistant to one or more antibiotics, with 94% being resistant to cephalothin, 27% resistant to tetracycline, and 15% resistant to ampicillin. Furthermore, on an average over all three sites, a large number of the water isolates demonstrated multidrug-resistance with 34% resistant to =2 antibiotics and 11% resistant to =3 antibiotics. All of the soil isolates exhibiting antibiotic resistance were resistant to the cephalothin (87%), but only ten of these isolates were multidrug-resistant (8.9%) - significantly less than that found within the water isolates. The pattern of high cephalothin resistance observed within both the soil and water isolates may suggest the presence of native populations of cephalothin-resistant E. coli within these sites. However, the higher rate of multidrug resistance observed within the water isolates when compared to the soil E. coli populations suggests the possibility that resistance sources other than just the soil contributed to antibiotic-resistant E. coli in runoff from these watersheds.