Irrigation waters and pipe-based biofilms as sources for antibiotic-resistant bacteria

Authors: BLAUSTEIN, RYAN - University Of Maryland; Shelton, Daniel; Van Kessel, Jo Ann; Karns, Jeffrey; MATT, STOCKER - Orise Fellow; Pachepsky, Yakov

Submitted to: Environmental Monitoring and Assessment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2015
Publication Date: 12/24/2015
Citation: Blaustein, R., Shelton, D.R., Van Kessel, J.S., Karns, J.S., Matt, S., Pachepsky, Y.A. 2015. Irrigation waters and pipe-based biofilms as sources for antibiotic-resistant bacteria. Environmental Monitoring and Assessment. 199(1):1-12.

Interpretive Summary: Antimicrobial resistance threatens the effective prevention and treatment of an ever-increasing range of infections caused by bacteria, parasites, viruses and fungi. Health hazards may arise due to the presence of antibiotic resistant bacteria in water used to irrigate produce. Pipes in irrigation systems have been shown to harbor microorganisms in biofilms on their walls and connectors. Microorganisms from the biofilms can subsequently be released to irrigation water. We hypothesize that the antibiotic resistance of bacteria in biofilms may change with time; therefore, biofilms may both amplify or diminish the antibiotic resistance of microorganisms reaching produce in irrigation water. We carried out experiments with an irrigation system taking water from a creek in Maryland. We monitored biofilm growth and concentrations of bacteria, as well as the resistance of E. coli, fecal coliforms, and total heterotrophic bacteria to a panel of 7 antibiotics, representing 5 antibiotic classes. We found that multiple-drug resistance was observed for all studied bacterial groups, most often for fecal coliforms, and the percentages of multiple-drug resistant total coliforms and fecal coliforms substantially changed from week to week. The results of this work indicate that antibiotic resistance is pervasive in urban/suburban watersheds. The results of this survey are important to producers, regulators, and consultants in that they document the presence of antibiotic resistance in irrigation waters used in produce farming.

Technical Abstract: The presence of antibiotic-resistant bacteria in environmental surface waters has gained recent attention. Wastewater- and drinking water distribution systems are known to disseminate antibiotic-resistant bacteria, with the biofilms that form on the inner-surfaces of the pipeline as a hotspot for proliferation and gene exchange. Pipe-based irrigation systems that utilize surface waters may contribute to the dissemination of antibiotic-resistant bacteria in a similar manner. We conducted irrigation events at a perennial stream on a weekly basis for one month, and the concentrations of total heterotrophic bacteria, total coliforms, and fecal coliforms, as well as the concentrations of these bacterial groups that were resistant to ampicillin and tetracycline were monitored at the intake water. Just before each of the latter three events, residual pipe water was sampled and 6 in. sections of pipeline (coupons) were detached from the system and biofilm from the inner-wall was removed and analyzed for total protein content and all of the above bacteria. Isolates of biofilm-associated bacteria were screened for resistance to a panel of 7 antibiotics, representing 5 antibiotic classes. All of the monitored bacteria grew substantially in the residual water between irrigation events and the biomass of the biofilm steadily increased from week to week. The percentages of biofilm-associated isolates that were resistant to antibiotics on the panel sometimes increased between events. Multiple-drug resistance was observed for all bacterial groups, most often for fecal coliforms, and the amounts of multiple-drug resistant total coliforms and fecal coliforms substantially changed from week to week. Results from this study highlight irrigation waters as a potential source for antibiotic-resistant bacteria, which can subsequently become incorporated into and proliferate within irrigation pipe-based biofilms.