Variations in Bacterial Communities and Antibiotic Resistance Genes Across Diverse Recycled and Surface Water Irrigation Sources in the Mid-Atlantic and Southwest United States: A CONSERVE Two-Year Field Study

Reduced availability of agricultural water has spurred increased interest in using recycled irrigation water for U.S. food crop production. However, there are significant knowledge gaps concerning the microbiological quality of these water sources. To address these gaps, we used 16S rRNA gene and metagenomic sequencing to characterize taxonomic and functional variations (e.g., antimicrobial resistance) in bacterial communities across diverse recycled and surface water irrigation sources. We collected 1 L water samples (n = 410) between 2016 and 2018 from the Mid-Atlantic (12 sites) and Southwest (10 sites) U.S. Samples were filtered, and DNA was extracted. The V3-V4 regions of the 16S rRNA gene were then PCR amplified and sequenced. Metagenomic sequencing was also performed to characterize antibiotic, metal, and biocide resistance genes. Bacterial alpha and beta diversities were significantly different (p < 0.001) across water types and seasons. Pathogenic bacteria, such as Salmonella enterica, Staphylococcus aureus, and Aeromonas hydrophilia were observed across sample types. The most common antibiotic resistance genes identified coded against macrolides/lincosamides/streptogramins, aminoglycosides, rifampin and elfamycins, and their read counts fluctuated across seasons. We also observed multi-metal and multi-biocide resistance across all water types. To our knowledge, this is the most comprehensive longitudinal study to date of U.S. recycled water and surface water used for irrigation. Our findings improve understanding of the potential differences in the risk of exposure to bacterial pathogens and antibiotic resistance genes originating from diverse irrigation water sources across seasons and U.S. regions.

Longitudinal Assessment of the Dynamics of Escherichia coli, Total Coliforms, Enterococcus spp., and Aeromonas spp. in Alternative Irrigation Water Sources: a CONSERVE Study

As climate change continues to stress freshwater resources, we have a pressing need to identify alternative (nontraditional) sources of microbially safe water for irrigation of fresh produce. This study is part of the center CONSERVE, which aims to facilitate the adoption of adequate agricultural water sources. A 26-month longitudinal study was conducted at 11 sites to assess the prevalence of bacteria indicating water quality, fecal contamination, and crop contamination risk (Escherichia coli, total coliforms [TC], Enterococcus, and Aeromonas). Sites included nontidal freshwater rivers/creeks (NF), a tidal brackish river (TB), irrigation ponds (PW), and reclaimed water sites (RW). Water samples were filtered for bacterial quantification. E. coli, TC, enterococci (∼86%, 98%, and 90% positive, respectively; n = 333), and Aeromonas (∼98% positive; n = 133) were widespread in water samples tested. Highest E. coli counts were in rivers, TC counts in TB, and enterococci in rivers and ponds (P < 0.001 in all cases) compared to other water types. Aeromonas counts were consistent across sites. Seasonal dynamics were detected in NF and PW samples only. E. coli counts were higher in the vegetable crop-growing (May-October) than nongrowing (November-April) season in all water types (P < 0.05). Only one RW and both PW sites met the U.S. Food Safety Modernization Act water standards. However, implementation of recommended mitigation measures of allowing time for microbial die-off between irrigation and harvest would bring all other sites into compliance within 2 days. This study provides comprehensive microbial data on alternative irrigation water and serves as an important resource for food safety planning and policy setting.IMPORTANCE Increasing demands for fresh fruit and vegetables, a variable climate affecting agricultural water availability, and microbial food safety goals are pressing the need to identify new, safe, alternative sources of irrigation water. Our study generated microbial data collected over a 2-year period from potential sources of irrigation (rivers, ponds, and reclaimed water sites). Pond water was found to comply with Food Safety Modernization Act (FSMA) microbial standards for irrigation of fruit and vegetables. Bacterial counts in reclaimed water, a resource that is not universally allowed on fresh produce in the United States, generally met microbial standards or needed minimal mitigation. We detected the most seasonality and the highest microbial loads in river water, which emerged as the water type that would require the most mitigation to be compliant with established FSMA standards. This data set represents one of the most comprehensive, longitudinal analyses of alternative irrigation water sources in the United States.

Cold Atmospheric Plasma Jet Inactivates Cryptosporidium parvum Oocysts on Cilantro

ABSTRACT

Cilantro was recently identified as a vehicle for protozoan illness. Current postharvest practices are not sufficient to inactivate protozoa on cilantro. Cold plasma is an emerging nonthermal waterless technology with potential applications in food processing that are currently being investigated to enhance the safety of herbs. The purpose of this study was to determine the impact of cold atmospheric plasma (CP) on the viability of Cryptosporidium parvum oocysts on cilantro. C. parvum oocysts were inoculated onto cilantro and treated with a CP jet for 0, 30, 90, and 180 s at a working distance of 10 cm with a flow of 1.42 × 10-3 m3/s. Oocyst viability was determined using HCT-8 cell culture infectivity assays. Overall, each treatment significantly reduced oocyst infectivity compared with the 0-s treatment control (P ≤ 0.02). Log inactivations of oocysts observed on cilantro were 0.84, 1.23, and 2.03 for the 30-, 90-, and 180-s treatment times, respectively. Drying and darkening of cilantro leaves was observed with treatments longer than 30 s. CP can reduce C. parvum infectivity on cilantro. With further research and optimization, this treatment technology has potential applications in postharvest processing of cilantro.

HIGHLIGHTS

Pharmaceuticals, herbicides, and disinfectants in agricultural water sources

Agricultural water withdrawals account for the largest proportion of global freshwater use. Increasing municipal water demands and droughts are straining agricultural water supplies. Therefore, alternative solutions to agricultural water crises are urgently needed, including the use of nontraditional water sources such as advanced treated wastewater or reclaimed water, brackish water, return flows, and effluent from produce processing facilities. However, it is critical to ensure that such usage does not compromise soil, crop, and public health. Here, we characterized five different nontraditional water types (n = 357 samples) for the presence of pharmaceuticals, herbicides, and disinfectants using ultra-high-pressure liquid chromatography tandem mass spectrometry based method (UPLC-MS/MS). We then evaluated whether the levels of these contaminants were influenced by season. The highest level of herbicides (atrazine) was detected in untreated pond water (median concentration 135.9 ng/L). Reclaimed water had the highest levels of antibiotics and stimulants including azithromycin (215 ng/L), sulfamethoxazole (232.1 ng/L), and caffeine (89.4 ng/L). Produce processing plant water also tended to have high levels of atrazine (102.7 ng/L) and ciprofloxacin (80.1 ng/L). In addition, we observed seasonal variability across water types, with the highest atrazine concentrations observed during summer months, while the highest median azithromycin concentrations were observed in reclaimed water during the winter season. Further studies are needed to evaluate if economically feasible on-farm water treatment technologies can effectively remove such contaminants from nontraditional irrigation water sources.

The efficacy of zero valent iron-sand filtration on the reduction of Escherichia coli and Listeria monocytogenes in surface water for use in irrigation

The use of surface and recycled water sources for irrigation can reduce demand on critical groundwater resources. Treatment or mitigation may be necessary for the use of these alternative water sources in order to reduce risk associated with microbial pathogens present in the water. In this study, the efficacy of a zero-valent iron (ZVI) sand filter was assessed for the reduction of Listeria monocytogenes and Escherichia coli in surface water. Water recovered from an agricultural pond was inoculated with E. coli TVS353 and an environmental L. monocytogenes isolate at 7 Log10 CFU/mL and horizontally filtered over a six-month period through a PVC pipe filter, filled with 35%:65% (volume:volume) ZVI:sand or sand alone. Filtered water was used to irrigate lettuce and bacterial persistence on lettuce leaves was determined for 7 days post-irrigation. Both ZVI:sand-filtered water and sand-filtered water contained significantly (p < 0.005) lower levels of E. coli and L. monocytogenes compared to initial unfiltered inoculated water. Population reductions of E. coli and L. monocytogenes were comparable after sand filtration. However, ZVI:sand filtration resulted in significantly greater population reductions of L. monocytogenes (P < 0.05) compared to E. coli. Populations of E. coli on leaves of lettuce plants irrigated with ZVI:sand-filtered water were not significantly lower than populations on plants irrigated with sand-filtered irrigation water over the 7-day period. However, populations of L. monocytogenes on lettuce leaves irrigated with ZVI-treated water were significantly lower than counts on plants irrigated with sand-filtered irrigation water on days 3 and 4 post irrigation (p = 0.052 and p = 0.042 for days 3 and 4, respectively. The differences observed in reductions of L. monocytogenes and E. coli by ZVI filtration is due to the differing effect that ZVI disruption has on Gram-positive and Gram-negative cell walls and membranes. ZVI- sand filters show promising results as an inexpensive on-farm technology for the mitigation of enteric foodborne bacterial populations in pond water over a six-month period.

Prevalence of Shiga-toxigenic and atypical enteropathogenic Escherichia coli in untreated surface water and reclaimed water in the Mid-Atlantic U.S

The microbial quality of irrigation water has increasingly become a concern as a source of contamination for fruits and vegetables. Non-traditional sources of water are being used by more and more growers in smaller, highly diversified farms in the Mid-Atlantic region of the U.S. Shiga-toxigenic E. coli (STEC) have been responsible for several outbreaks of infections associated with the consumption of leafy greens. Our study evaluated the prevalence of the "big seven" STEC serogroups and the associated enterohemorrhagic E. coli (EHEC) virulence factors (VF) genes in conventional and nontraditional irrigation waters in the Mid-Atlantic region of the U.S. Water samples (n = 510) from 170 sampling events were collected from eight untreated surface water sites, two wastewater reclamation facilities, and one vegetable processing plant, over a 12-month period. Ten liters of water were filtered through Modified Moore swabs (MMS); swabs were then enriched into Universal Pre-enrichment Broth (UPB), followed by enrichment into non-O157 STEC R&F broth and isolation on R & F non-O157 STEC chromogenic plating medium. Isolates (n = 2489) from enriched MMS from water samples were screened for frequently reported STEC serogroups that cause foodborne illness: O26, O45, O103, O111, O121, O145, and O157, along with VF genes stx1, stx2, eae, and ehxA. Through this screening process, STEC isolates were found in 2.35% (12/510) of water samples, while 9.0% (46/510) contained an atypical enteropathogenic E. coli (aEPEC) isolate. The eae gene (n = 88 isolates) was the most frequently detected EHEC VF of the isolates screened. The majority of STEC isolates (stx1 or stx2) genes mainly came from either a pond or reclamation pond water site on two specific dates, potentially indicating that these isolates were not spatially or temporally distributed among the sampling sites. STEC isolates at reclaimed water sites may have been introduced after wastewater treatment. None of the isolates containing eae were determined to be Escherichia albertii. Our work showed that STEC prevalence in Mid-Atlantic untreated surface waters over a 12-month period was lower than the prevalence of atypical EPEC.

Type 2 diabetes mellitus is associated with increased axial bone density in men and women from the Hertfordshire Cohort Study: evidence for an indirect effect of insulin resistance?

AIMS/HYPOTHESIS

Previous studies have suggested that the high bone density often observed in type 2 diabetic patients may be explained by insulin resistance. We explored this hypothesis in the Hertfordshire Cohort Study.

METHODS

A total of 465 men and 444 women aged 59 to 71 years and with no prior diagnosis of diabetes attended a clinic where a glucose tolerance test was performed and bone density measured at the femoral neck and lumbar spine. Biochemical markers of bone turnover (serum osteocalcin and urinary mean c-terminal cross-linking telopeptide of type II collagen) were measured in 163 men.

RESULTS

According to WHO criteria, 83 men and 134 women were diagnosed with impaired glucose tolerance and a further 33 men and 32 women were diagnosed as having type 2 diabetes. Bone density was higher in newly diagnosed diabetic subjects, with relationships stronger in women (p<0.001) than men (p<0.05) and attenuated by adjustment for body mass index. In both sexes, we observed positive correlations between the total femur and femoral neck bone mineral density with measures of insulin resistance (r=0.17-0.22), with stronger results observed in women. These relationships did not apply after adjustment for body mass index. Glucose status did not lead to differences in osteocalcin level or c-terminal cross-linking telopeptide of type II collagen levels.

CONCLUSIONS/INTERPRETATION

Our findings suggest that hyperinsulinaemia may affect bone mineral density through indirect effects, e.g. body weight.