Microbiological safety of spinach throughout commercial supply chains in Gauteng Province, South Africa and characterization of isolated multidrug-resistant Escherichia coli.

Abstract

To investigate the microbiological quality, potential foodborne pathogen presence, and to phenotypically (antimicrobial resistance [AMR] profiles) and genotypically (DNA fingerprints and diarrhoeagenic genes) characterize Escherichia coli isolated throughout spinach production systems from farm-to-sale. Samples (n=288) were collected from two commercial supply chains using either river or borehole irrigation water. E. coli was enumerated throughout the chain where river water was directly used for overhead irrigation at levels between 0.00 and 3.22logcolony forming unit (CFU)g-1 . Following enrichment, isolation and matrix-assisted laser desorption ionization time-of-flight mass spectrometry identification, E. coli was isolated from 22.57% (n=65/288) of all samples. Salmonella spp. were isolated from 3% (n=9/288) of river and irrigation water samples on one farm, and no Listeria monocytogenes was detected throughout the study. Of the 80 characterized E. coli isolates, one harboured the stx2 virulence gene, while 43.75% (n=35) were multidrug resistant. Overall, 26.30% of the multidrug-resistant E. coli isolates were from production scenario one that used river irrigation water, and 17.50% from the second production scenario that used borehole irrigation water. A greater percentage of resistance phenotypes were from water E. coli isolates (52.50%), than isolates from spinach (37.50%). E. coli isolates from spinach and irrigation water clustered together at high similarity values (>90%) using enterobacterial repetitive intergenic consensus-polymerase chan reaction analysis. This study reported the presence of multidrug-resistant environmental E. coli throughout spinach production from farm, during processing and up to retail. Furthermore, the similarity of multi-drug resistant E. coli isolates suggests transfer from irrigation water to spinach in both scenarios, reiterating that irrigation water for vegetables consumed raw, should comply with standardized microbiological safety guidelines. Multidrug-resistant E. coli presence throughout spinach production emphasizes the necessity of increased surveillance of AMR in fresh produce and the production environment within a One Health paradigm to develop AMR mitigation strategies.