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.

Estudio microbiológico de ajo(Allium sativum L.) y cebolla (Allium cepa L.) deshidratados / Microbiological study of garlic (Allium sativum L.) and onion (Allium cepaL.) dehydrated

En este trabajo se efectuó un estudio microbiológico durante la deshidratación y el almacenamiento de ajo (Allium sativum L.) y de cebolla (Allium cepa L.). Al ajo se le efectuó un proceso de escaldado y a la cebolla un salmuereado previo a la deshidratación. En las materias primas los recuentos promedio expresados en UFC/g fueron: bacterias aerobias mesófilas entre 1,2 x 102y 1,6 x 103, mohos y levaduras entre 60 y 1,6 x 103, Lactobacillus spp. y Leuconostocmesenteroidessubesp. mesenteroides entre 10 y 50.Se identificaron: Penicillium spp., Monilia spp. Lactobacillus brevis,Leuconostoc mesenteroides subesp. mesenteroides y levaduras en ajo; Mucor spp., Penicillium spp., Monilia spp., Lactobacillus brevis y levaduras en dos tipos de cebolla. Leuconostoc mesenteroides subesp. mesenteroides sólo se detectó en un tipo de cebolla. En ajos deshidratados y durante el almacenamiento se hallaron Penicillium spp., Monilia spp., Lactobacillus brevis y levaduras mientras que los mismos con escaldado no presentaron desarrollo. Mucor spp., Penicillium spp., Monilia spp. y Lactobacillus brevis se identificaron en los dos tipos de cebolla deshidratadas. Con la incorporación del salmuereado la microflora se redujo significativamente hallándose solamente Penicillium spp. La utilización de barreras adicionales de control microbiano tales como escaldado y salmuereado produce un aporte importante a la estabilidad microbiológica de los productos.

A microbiological study during the process and the storage of garlic (Allium sativum L.) and onion (Allium cepa L.) dehydrated, with the additional barriers of blanching or brine immersion, was made. In all raw materials the average counts of aerobic mesophilic bacteria expressed in CFU/g ranged from 1.2 x 102to 1.6 x 103, molds and yeasts from 60 to 1.6 x 103, Lactobacillus spp. and Leuconostocmesenteroides subsp. mesenteroides between 10 and 50. Microorganisms identified were Penicillium spp., Monilia spp., Lactobacillus brevis, Leuconostoc mesenteroides subsp. mesenteroides and yeasts in garlic; Mucor spp., Penicillium spp., Monilia spp., Lactobacillus brevis and yeasts in both types of onions. Leuconostoc mesenteroides subsp. mesenteroides was detected in only kind of onion. In dehydrated garlic storage, Penicillium spp., Monilia spp., Lactobacillus brevis and yeasts were detected. In garlic, when a blanching step was carried out no microflora was detected. Mucor spp., Penicillium spp., Monilia spp. and Lactobacillus brevis were identified in both types of dehydrated onions. When brine immersion was included the microflora detected was significantly lower and only Penicillium spp. were found. The use of additional barriers such as blanching or brine immersion produces an important effect on the microbiological stability in these products.