Incidence of fecal indicator and pathogenic bacteria in reclaimed and return flow waters in Arizona, USA

Authors: ZHU, LIBIN - University Of Arizona; TORRES, MONIQUE - University Of Arizona; BETANCOURT, WALTER - University Of Arizona; Sharma, Manan; MICALLEF, SHIRLEY - University Of Maryland; GERBA, CHARLES - University Of Arizona; SAPKOTA, AMY - University Of Maryland; SAPKOTA, AMIR - University Of Maryland; PARVEEN, SALINA - University Of Maryland Eastern Shore (UMES); MAY, ERIC - University Of Maryland Eastern Shore (UMES)

Submitted to: Environmental Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2018
Publication Date: 12/1/2018
Citation: Zhu, L., Torres, M., Betancourt, W.Q., Sharma, M., Micallef, S.A., Gerba, C., Sapkota, A.R., Sapkota, A., Parveen, S., May, E. 2018. Incidence of fecal indicator and pathogenic bacteria in reclaimed and return flow waters in Arizona, USA. Environmental Research. 170:122-127. https://doi.org/10.1016/j.envres.2018.11.048.
DOI: https://doi.org/10.1016/j.envres.2018.11.048

Interpretive Summary: As the availability of irrigation water receives more and more attention, additional sources other than groundwater are being evaluated for the suitability to grow fruits and vegetables. This study evaluated different sources of irrigation water, including reclaimed water and return flows, in Arizona to determine if they contained enteric bacterial pathogens that may be transferred to fruits and vegetables consumed raw. Reclaimed water showed the presence of fecal contamination indicators like Escherichia coli and Enterococcus spp, but no Salmonella enterica or Listeria monocytogenes. Results shows that Salmonella enterica was the most commonly detected pathogen in the return flows, while no Listeria monocytogenes was found from those sources. Overall, more samples are needed to truly evaluate and quantify the risk of bacterial pathogens present in return flows and reclaimed water that may potentially used on fruit and vegetable plants. The research presented here will benefit farmers as it used novel methods that were used to quantify the presence of bacterial pathogen in return flows and reclaimed waters, which can be applied to other geographic regions and water sources.

Technical Abstract: The quality of irrigation water used to cultivate produce that is consumed raw is an important issue with regard to food safety. In this study, the microbiological quality of potential irrigation water sources in Arizona was evaluated by testing for the presence of indicator and pathogenic bacteria. Reclaimed water samples were collected from two wastewater treatment plants and return flow samples were collected from two drainage canals and one return flow pond. Standard membrane filtration methods were used for detection of indicator bacteria. Water samples (n=28) were filtered through cellulose ester membrane filters. Each filter was placed on agar medium selective for Escherichia coli/total coliforms or Enterococcus spp., and bacteria were enumerated after incubation for 20-24 h. For detection of pathogens (Salmonella enterica, Listeria monocytogenes and Shiga toxin-producing E. coli (STEC)), water samples were filtered through Modified Moore swabs and enriched in Universal Pre-Enrichment Broth, followed by selective enrichment broth for each pathogen. The enriched broth was streaked onto agar media selective for each pathogen. Presumptive colonies were confirmed by PCR/real-time PCR. Among the 14 reclaimed water samples from two sites, the ranges of recovered populations of E. coli, total coliforms, and enterococci were 0-1.3, 0.5-8.3X10^3, and 0-5.5 CFU/100 mL, respectively. No L. monocytogenes, Salmonella or STEC were found. In the 13 return flow water samples from 3 sites, the ranges of recovered populations of E. coli, total coliforms and enterococci were 1.9- 5.3X10^2, 6.5X10^2-9.1X10^4, and 3.7-2.9X10^3 CFU/100 mL, respectively. All samples were negative for L. monocytogenes. One (7.1%) of the return flow samples was positive for E. coli O145. Nine (64.3%) of the samples were positive for Salmonella. Both real-time PCR and culture-based methods were used for the detection of Salmonella and L. monocytogenes, and the results from the two methods were comparable. The findings of this study provide evidence that irrigation waters in Arizona, including reclaimed water and return flows, could be potential sources of bacterial contamination of produce. Additional work is needed to evaluate whether bacteria present in irrigation water sources transfer to the edible portion of irrigated plants and are capable of persisting through postharvest activities.