Growth kinetics of Escherichia coli O157: H7 on the epicarp of fresh vegetables and fruits

ABSTRACT Despite the increasing reports on the incidence of fresh vegetables and fruits as a possible vehicle for human pathogens, there is currently limited knowledge on the growth potential of Escherichia coli O157:H7 on different plant substrates. This study analyzed the selective adhesion and growth of E. coli O157:H7 on chili habanero (Capsicum chinense L.), cucumber (Cucumis sativus), radish (Raphanus sativus), tomato (Lycopersicon esculentum), beet (Beta vulgaris subsp. vulgaris), and onion (Allium cepa L.) under laboratory conditions. The Gompertz parameters were used to determine the growth kinetics. Scanning electron microscopy was used to visualize the adhesion of E. coli O157:H7 on the epicarp of the samples. Predictive models were constructed to compare the growth of E. coli O157:H7 on the samples with different intrinsic factors and to demonstrate the low selectivity of the pathogen. No significant difference was observed in the lag-phase duration (LPD), generation time (GT), and exponential growth rate (EGR) of the pathogen adhered to the samples. The interaction between the microorganism and the substrate was less supportive to the growth of E. coli O157:H7 for onion, whereas for tomato and cucumber, the time for the microorganism to attain the maximum growth rate (M) was significantly longer than that recorded for other samples.

Influence of raw meat natural background flora on growth of Escherichia coli 0157: H7 in ground beef

Escherichia coli 0157 : H7 foodborne pathogen of increasing importance. It has been involved in several threatening outbreaks, most of them associated with meat products. In this study, the influence of some bacteria from the natural background flora of raw meat over E.coli 0157 : H7 in ground beef stored under refrigeration and at room temperature was evaluated. Different levels of E.coli 0157 : H7 (10 1 - 10 2, 10 3 - 10 4, and 10 6 - 10 7 CFU/g), inoculated in ground beef samples, were challenged with strains of non-pathogenic E.coli, Psudomonas putida or Leuconostoc sp. Growth of the pathogen was monitored using standard cultural methods and an Elisa-type rapid method. Non-pathogenic E.coli, Pseudomonas putida and Leuconostoc sp. did not affect growth of E.coli 0157 : H7 in ground beef, both under refrigeration and at room temperature. Based on these findings, the low occurrence of E.coli 0157 : H7 in raw meat may not be attributed to antagonistic effects of bacteria from the natural background flora.