Exploratory study into the microbiological quality of spinach and cabbage purchased from street vendors and retailers in Johannesburg, South Africa

Abstract

Knowledge of the microbiological quality, prevalence of antibiotic resistance and virulence genes in bacterial isolates from leafy green vegetables supplied by formal (retailers) and informal (street vendors) suppliers in South Africa is limited. Since leafy vegetables have been implicated in food borne disease outbreaks world-wide, a total of 180 cabbage and spinach samples were collected from 3 major retailers and 9 street vendors in Johannesburg, SA. Escherichia coli and coliforms were enumerated using 3M Petrifilm count plates. The prevalence of Listeria monocytogenes, Salmonella spp. and Shigella spp. were determined using real-time PCR analysis. Identities of presumptive E. coli isolates from the fresh produce were confirmed using MALDI-TOF MS. Isolates were characterized using phenotypic (antibiotic resistance) and genotypic (phylogenetic, virulence gene) analysis. Hygiene indicator bacteria levels on spinach from formal and informal retailers exceeded the maximum level specified by the Department of Health guidelines for fresh fruit and vegetables. Street vendor spinach E. coli counts were higher (p= < 0.0789) than retailer spinach counts. E. coli was present in 2 cabbage samples only at 0.0035 CFU/g. L. monocytogenes and Salmonella spp. were detected in 7.2% and 5% of the 180 samples respectively using real-time PCR analysis, while Shigella was not detected. Of the 29 spinach E. coli isolates 37.9% were multi-drug resistant. Virulence genes eae and stx1 were present in 14% and 3% of the spinach E. coli isolates respectively, while the stx2 gene was not detected. Eighty-six percent (86%) of these isolates belonged to phylogroup A, 3% to group C, 7% to group E and 3% to clade 1. The results from the current exploratory study on the microbiological quality of spinach bought from selected retailers highlighted the need for continued surveillance on a larger scale, especially in the informal sector, in order to characterize the potential risk to the consumer.