Microbiological survey of imported produce available at retail across Canada

Abstract

Increasing consumption and year-round consumer demand for fresh, minimally processed green vegetables have been observed in Canada and other developed countries. However, in the past two decades, produce has been increasingly implicated in outbreaks and correspondingly recognized as a vector for the transmission of pathogenic microorganisms. To this end, we examined the microbiological quality of imported produce available at retail across Canada during a period of limited domestic availability. In total, 106 samples obtained from five Canadian cities were purchased from retail outlets and subjected to microbiological analyses, including aerobic plate (APC) and coliform counts, and enrichments for enterococci, indicator Escherichia coli, E. coli O157:H7 and Salmonella spp. Also, recovered Enterococcus faecalis and Enterococcus faecium were screened for antimicrobial resistance (AMR). Overall, samples included herbs (n=61), leafy greens (n=25), and spinach (n=20) deriving from five countries (Columbia, Dominican Republic, Guatemala, Mexico, and the United States [US]). APCs were consistent across commodities regardless of country, ranging from mean log10CFU/g of 6.1 to 7.4, with no significant differences observed. Excluding a single leafy green sample from Guatemala, the lowest prevalence of coliforms was for Mexican herbs (22.2%), with a high of 66.7% on US leafy greens. With the exception of spinach, concentrations of coliforms varied widely, ranging from undetectable to too numerous to count (>8.5log10CFU/g). Of the commodities assessed, Mexican and US spinach had the lowest coliform concentrations (undetectable to 4.0log10CFU/g). Organic herbs and conventional leafy greens possessed significantly lower (p<0.05) prevalence of coliforms compared to conventional herbs and organic leafy greens, respectively. The most frequent recovery of indicator E. coli was observed for herbs, with 11.1, 8.3, and 3.7% prevalence observed in samples from Columbia, US, and Mexico, respectively. For spinach, 0 and 6.7% of Mexican and US samples tested positive, while no leafy green samples from either country were positive. No E. coli O157:H7 or Salmonella spp. were detected. E. faecium and E. faecalis were recovered from 15.1 and 5.7% of samples, respectively. Although no glycopeptide resistance was observed, resistance to other clinically relevant antibiotics was noteworthy in both species. Overall, though microbiological quality indicators were frequently high, E. coli O157:H7 and Salmonella were not detected. However, the presence of resistance and reduced susceptibility to clinically relevant antimicrobials in recovered enterococci demonstrate imported fresh produce may serve as a vehicle for the transmission of antimicrobial resistance across national borders.