Multidrug Resistance and High Prevalence of class 1 Integrons in Escherichia coli Isolated from Irrigation Water and Vegetables in Parts of Nsukka and Enugu, Nigeria
Authors: Chigor Chinyere B. , Ibangha Ini‐Abasi I , Onuora Valentino C , Omotosho Omolola E , Chernikova Tatyana , Chigor Vincent N , Golyshin Peter 
Published: November 2023

The contamination of fresh produce by irrigation waters has led to outbreaks of foodborne illness, yet treated wastewater presents itself as an attractive alternative to scarce quality water in the developing countries. Horizontal transfer of integrons play important role in the spread and maintenance of antimicrobial resistance among the Enterobacteriaceae.

Study objective

This study assessed the effluent from the University of Nigeria, Nsukka Wastewater Treatment Plant (UNN‐WWTP) as well as vegetables irrigated with the effluent and vegetables sold in selected markets for the presence of Escherichia coli and determined the prevalence integrons in multidrug‐resistant isolates.

Methods

Isolation and identification of presumptive E. coli was done using Eosin Methylene Blue (EMB) agar plates and the Gram‐staining procedure. The confirmation of E. coli and enterotoxigenic E. coli (ETEC) strain were achieved by polymerase chain reaction (PCR) detection of the target beta‐glucuronidase (uidA) and heat‐labile toxin (lt) genes respectively. Resistance to antibiotics was determined using the Bauer‐Kirby disk diffusion method and the Clinical and Laboratory Standard Institute criteria. Integrons were detected by multiplex PCR using primers specific for class 1 and 2 integrons.

Results

A total of the 178 E. coli isolates were obtained from WWTP effluent (41), Greenhouse vegetables (46), Farm vegetables (55) and Market vegetables (36). Twenty‐three of these 178 isolates (12.9%) were confirmed to be enterotoxigenic E. coli (ETEC) strains. The isolation rates of ETEC for the different sample types were: WWTP effluent, 20% (n=60), Greenhouse vegetables 8.3% (n=60), Farm vegetables 4.8% (n=84), and Market vegetables 2.4% (n=84). All the isolates were multi‐drug resistant. The most frequent resistance types in the 178 E. coli isolates were: Cloxacillin (100%), Metronidazole (100%), Vancomycin (98.8%), Erythromycin (94.3%), and Clarithromycin (89.6%). Multi‐drug resistance (MDR) was detected in isolates from all sources, ranging from a five‐drug resistance observed in a single isolate to 16‐drug resistance patterns found in two different isolates. Of the 178 E. coli isolates, class 1 integrons were detected in 175 (98.3%), and class 2 integrons were detected on 5 (2.8%). All the class 2 integrons were found in isolates that were positive for class 1.

Conclusions

The high detection rates for E. coli in the studied effluent and vegetable samples represent potential public health hazards heightened by observed multidrug resistance in all the isolates and the high prevalence of class 1 integrons. It is concluded that UNN‐WWTP is a significant reservoir for diarrheagenic E. coli. Vegetable farming at the site should therefore be discontinued as it presents significant threat to the health of consumers of such vegetables.

Support or Funding Information

The British Council Researcher Links Travel Grant (2014)