Background:
Water scarcity has increased the use of wastewater (WW) for irrigation, especially in low/middle-income countries. However, WW irrigation poses risks, such as the spread of antimicrobial-resistant bacteria (ARBs) and pathogens like coliforms into the food chain. Humans are exposed to ARBs through cilantro consumption or indirectly via contact with alfalfa-fed livestock.
Hypothesis and Material/Method:
This study examined the presence of coliform ARBs in irrigation waters, including untreated WW (UWW), treated WW (TWW), groundwater (GW), spring water (SW), and irrigated crops (cilantro, alfalfa) collected in the Mezquital Valley, Mexico. We focused on the cultivation of bacteria colonizing the endosphere or strongly attached to the surface of leaves. We hypothesized that, (I) irrigation water quality influences the spread of coliform ARBs to plants, and (II) plants irrigated with TWW may harbour ARBs with a higher degree of multi-resistance due to potential horizontal gene transfer during WW treatment, compared to those irrigated with UWW, GW and SW.
Result and Conclusion:
Extended spectrum β-lactamase producing (ESBL) and carbapenem-resistant (CR) E. coli were cultivated by selective pre-enrichment and subsequent isolation on selective E. coli media. E. coli were identified by uidA PCR and MALDI-TOF MS. A total of 210 ESBL (130 alfalfa, 24 cilantro, 20 UWW, 18 per TWWs) and 40 CR E. coli (22 alfalfa, 14 UWW, 4 TWW) were isolated. ESBL/CR E. coli were not cultured from GW and SW. So far, WW treatment showed no significant effect on the multi-resistance of E. coli. Multi-resistance of E. coli isolated from alfalfa and cilantro was slightly lower compared to WW E. coli (without significant differences), depending on irrigation water quality or manure application[Office1] . Both, WW derived irrigation water and manure were determined as sources of multi-resistant E. coli in the studied crops. The E. coli strains will be characterized in more detail by genome sequencing.