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Persistence of Bacteroidales and other fecal indicator bacteria on inanimated materials, melon and tomato at various storage conditions

Ordaz, Gilberto, Merino-Mascorro, José Ángel, García, Santos, Heredia, Norma
International journal of food microbiology 2019 v.299 pp. 33-38
Bacteroidales, Enterococcus faecalis, Escherichia coli, cattle, cellulose, cork, esters, feces, filters, foods, genetic markers, host specificity, indicator species, melons, quantitative polymerase chain reaction, relative humidity, storage conditions, swine, tomatoes
In order to determine the microbial safety of produce, conventional fecal indicator bacteria (CFIB) such as Escherichia coli and Enterococcus are quantified as a standard practice. Bacteroidales are also fecal indicators mostly used for water samples; however, their use and persistence in foods has been rarely studied. In this study, persistence of both CFIB and genetic markers of host-specific Bacteroidales was determined in artificially contaminated materials and vegetables with different textured surfaces under different storage conditions. Sterile feces were contaminated with E. coli, E. faecalis, Bacteroidesthetaiotaomicron (human origin), and Bacteroidales from porcine and bovine origin. Feces were applied to filters of mixed cellulose esters and tomatoes (smooth surface) and flat cork coupons and melons (rough surface) and stored at 10 °C/95% relative humidity (RH) and 25 °C/65%RH for up to 25 days. Bacteroidales markers were analyzed by real-time polymerase chain reaction (qPCR), whereas CFIB were plated onto selective agars. CFIB detection on filters and cork surfaces declined over time. E. coli decreased 2.9 log CFU and 1.2 log CFU per filter and cork, respectively, at 10 °C/95%RH and 5.8 log CFU and 1.8 log CFU per filter and cork, respectively, at 25 °C/65%RH. E. faecalis decreased 1.9 log CFU on filters and 1.3 log CFU on cork at 10 °C/95%RH and 2.6 log CFU/filter and cork under both storage conditions. Although E. coli levels in tomatoes slightly increased during storage, the levels decreased by the end of the assays. However, CFIB levels in melons stored at 10 °C/95%RH increased after 20 days; when stored at 25 °C/65%RH, these levels increased after five days.Bacteroidales levels (universal and host-specific markers) in inanimated material and produce did not show significant differences (P ≤ 0.01) over time. Stability and persistence of Bacteroidales genetic markers make them superior to CFIB as markers and are alternatives for determining the risk of exposure to feces-contaminated produce.