Penetration of Escherichia coli O157:H7 into Lettuce Tissues as Affected by Inoculum Size and Temperature and the Effect of Chlorine Treatment on Cell Viability

Abstract

Penetration of Escherichia coli O157:H7 into iceberg lettuce tissues and the effect of chlorine treatment on cell viability were evaluated. Attachment of different inoculum levels (10(9), 10(8), and 10(7) CFU/ml) was examined by determining the number of cells at the surface and the cut edge of lettuce leaves (2 by 2 cm). E. coli O157:H7 attached preferentially to cut edges at all inoculum levels, with greater attachment per cm2 of lettuce at higher inoculum levels. A longer attachment time allowed more cells to attach at both sites. Immunostaining with a fluorescein isothiocyanate-labeled antibody revealed that cells penetrated into lettuce leaves from cut edges. Cells showed greater penetration when lettuce was held at 4 degrees C compared with 7, 25, or 37 degrees C and were detected at an average of 73.5 +/- 16.0 microm below the surfaces of cut tissues. Penetrating cells were mostly found at the junction of lettuce cells. The viability of attached cells after treatment with 200 mg/liter (200 ppm) of free chlorine for 5 min was examined by plating on tryptic soy agar and by a nalidixic acid elongation method. Although chlorine treatment caused significant reduction in attachment (0.7- and 1.0-log reduction at surfaces and cut edges, respectively), cells remained attached at high numbers (7.9 and 8.1 log CFU/cm2 at surfaces and cut edges, respectively). Elongated cells were observed in stomata and within the tissues of the lettuce, indicating they were protected from contact with chlorine.

Colonization of Arabidopsis thaliana with Salmonella enterica and Enterohemorrhagic Escherichia coli O157:H7 and Competition by Enterobacter asburiae

“…10 bacteria) that disinfection is often not practical without destroying the produce (42) or inhibiting germination (44). Furthermore, since penetration of E. coli O157:H7 into plant tissue has been demonstrated, disinfection of the tissue may not be effective (31,51,55,62). Alternative intervention measures have targeted prevention of the initial infestation.…”

Sanitização de alface americana com água ozonizada para inativação de Escherichia coli O157:H7

“…Takeuchi & Frank [20] evidenciaram que E. coli O157:H7 penetra nos tecidos atingindo uma profundidade de até 73 µm e se aloja preferencialmente na junção das células da alface. Os autores demonstraram que na profundidade de 30 a 40 µm, 68% das células de E. coli O157:H7 sobrevivem ao tratamento com 200 mg de cloro livre por litro, com redução de apenas 0,4 a 0,5 ciclos logarítmicos.…”

“…Os autores demonstraram que na profundidade de 30 a 40 µm, 68% das células de E. coli O157:H7 sobrevivem ao tratamento com 200 mg de cloro livre por litro, com redução de apenas 0,4 a 0,5 ciclos logarítmicos. Observa-se, que além da barreira física, a matéria orgânica que envolve as células reage com o sanitizante, reduzindo seu potencial antimicrobiano [20] .…”

Microbial ecology of fresh vegetables

“…Several innovative approaches both chemically and physically have been explored for the decontamination of fresh or fresh-cut vegetables (Table 17.5). Effective washing and decontamination of fresh-cut veg etables is difficult to achieve due to the different types of vegetables, the inadequate efficacy of individual treatments alone (Table 17.5), the presence of biofilms on vegetables and on processing equipment (Jahid and Ha, 2012;Somers et al, 1994), and internalization/infil tration of bacteria within produce (Zhuang et al, 1995;Zheng et al, 2013;Takeuchi and Frank, 2000). Therefore, a combination of different disinfection methods (e.g., hurdle technology) (Rico et al, 2007;Joshi et al, 2013) is necessary to increase the efficacy of disinfectants against microbial population reduction.…”