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

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.(AU)

Sobrevivência de Escherichia coli 0157: H7 em iogurtes com diferentes teores de açúcar / Survival of Escherichia coli 0157: H7 in yoghurts with different levels of sugar

The aim of this work was determine the viability of Escherichia coli 0157:H7 in yoghurt with different concentrations of sucrose (O, 10 and 15%) during 30 days of storage under refrigeration at 4.0°C±2.0°C. There was no difference apparent in pH among the yoghurt types. Yoghurt with no sugar and with 10% sucrose presented initially pH 4.52 and 4.44, respectively, and dropped in both to 4.32 at the end of storage. Yoghurt with 15% sucrose presented initial and final pH of 4.40 and 4.16, respectively. The acid lactic was 0.64 ± 0.04% on day O for three yoghurt types and there was no great variation during the time. Streptococcus thermophilus remained the 30 days of storage with log 9.0 CFU/mL and Lactobacillus bulgaricus about log 8.0-9.0 CFU/mL in all yoghurts. E. coli 0157:H7 survival S, 7and 8 days in yoghurt with O, 10% and 15% of sucrose, respectively. It was observed that the greater survival of pathogen occurred in yoghurt with more content of sucrose. (AU)

O objetivo do presente trabalho foi determinar a viabilidade de Escherichia coli 0157:H7 em iogurtes com diferentes concentrações de sacarose (O, 10, 15%) durante 30 dias de estocagem sob refrigeração a 4,0°C±2,0°C. Não houve diferença aparente no pH entre os tipos de iogurte. Iogurte sem açúcar e com 10% de sacarose apresentaram inicialmente pH de 4,52 e 4,44, respectivamente, caindo para 4,32 no final da estocagem; o pH baixou de 4,40 a 4,16 em iogurte com 15% de sacarose. Os três tipos de iogurte apresentaram 0,64±0,04% de ácido lático e não houve grande alteração com o tempo de refrigeração. S. thermophilus permaneceu os 30 dias de estocagem com log 9,0 UFC/mL e L bulgaricus entre log 8,0-9,0 UFC/rnL em todos os iogurtes. E. coli 0157:H7 sobreviveu 5, 7 e 8 dias em iogurte com 0, 10 e 15% de sacarose, respectivamente. Observou-se que a maior sobrevivência do patógeno ocorreu em iogurte com maior teor de açúcar. (AU)