Microbiological quality of irrigation water on highly diverse fresh produce smallholder farms: elucidating environmental routes of contamination.

Publisher: Oxford University Press Country of Publication: England NLM ID: 9706280 Publication Model: Print Cited Medium: Internet ISSN: 1365-2672 (Electronic) Linking ISSN: 13645072 NLM ISO Abbreviation: J Appl Microbiol Subsets: MEDLINE

Publication: 2022- : Oxford : Oxford University Press
Original Publication: Oxford : Published for the Society for Applied Bacteriology by Blackwell Science, c1997-

Agricultural Irrigation* ; Farms* ; Escherichia coli*/isolation & purification ; Escherichia coli*/genetics ; Soil Microbiology* ; Water Microbiology*; Salmonella/isolation & purification ; Salmonella/genetics ; Vegetables/microbiology ; Food Microbiology

Aim: To evaluate the microbiological safety, potential multidrug-resistant bacterial presence and genetic relatedness (DNA fingerprints) of Escherichia coli isolated from the water-soil-plant nexus on highly diverse fresh produce smallholder farms.
Methods and Results: Irrigation water (n = 44), soil (n = 85), and fresh produce (n = 95) samples from six smallholder farms with different production systems were analysed for hygiene indicator bacterial counts and the presence of shigatoxigenic E. coli and Salmonella spp. using standard microbiological methods. Identities of isolates were confirmed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), and the genetic relatedness of the E. coli isolates determined using enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) analysis. Irrigation water E. coli levels ranged between 0 and 3.45 log MPN/100 ml-1 with five farms having acceptable levels according to the World Health Organization limit (3 log MPN/100 ml-1). Fresh produce samples on four farms (n = 65) harboured E. coli at low levels (<1 log CFU/g-1) except for one sample from kale, spring onion, green pepper, onion, and two tomato samples, which exceeded international acceptable limits (100 CFU/g-1). Only one baby carrot fresh produce sample tested positive for Salmonella spp. Of the 224 samples, E. coli isolates were identified in 40% (n = 90) of all water, soil, and fresh produce types after enrichment. Additionally, the DNA fingerprints of E. coli isolates from the water-soil-plant nexus of each respective farm clustered together at high similarity values (>90%), with all phenotypically characterized as multidrug-resistant.
Conclusions: The clustering of E. coli isolated throughout the water-soil-plant nexus, implicated irrigation water in fresh produce contamination. Highlighting the importance of complying with irrigation water microbiological quality guidelines to limit the spread of potential foodborne pathogens throughout the fresh produce supply chain.
(© The Author(s) 2024. Published by Oxford University Press on behalf of Applied Microbiology International.)

2022/2023-00885 Water Research Commission; 20301 Centre of Excellence in Food Security; Centre for Environment, Fisheries and Aquaculture Science

Keywords: E. coli; antimicrobial resistance; food safety; irrigation water; microbial contamination

Date Created: 20240417 Date Completed: 20240427 Latest Revision: 20240427

20240427

10.1093/jambio/lxae091

38632044