Penetration of Escherichia coli O157:H7 into Lettuce as Influenced by Modified Atmosphere and Temperature

Abstract

The effects of temperature and atmospheric oxygen concentration on the respiration rate of iceberg lettuce and Escherichia coli O157:H7 cells attachment to and penetration into damaged lettuce tissues were evaluated. Respiration rate of lettuce decreased as the temperature was reduced from 37 to 10 degrees C. Reducing the temperature further to 4 degrees C did not affect the respiration rate of lettuce. Respiration rate was also reduced by lowering the atmospheric oxygen concentration. Lettuce was submerged in E. coli O157:H7 inoculum at 4, 10, 22, or 37 degrees C under 21 or 2.7% oxygen. Attachment and penetration of E. coli O157:H7 were not related to the respiration rate. The greatest numbers of E. coli O157:H7 cells attached to damaged lettuce tissues at 22 degrees C at both oxygen concentrations. More cells were attached under 21% oxygen than under 2.7% oxygen at each temperature, but this difference was small. Penetration of E. coli O157:H7 into lettuce tissue was determined by immunostaining with a fluorescein isothiocyanate-labeled antibody. Under 21% oxygen, E. coli O157:H7 cells showed greatest penetration when lettuce was held at 4 degrees C, compared to 10, 22. or 37 degrees C, and were detected at an average of 101 microm below the surfaces of cut tissues. However, under 2.7% oxygen, there were no differences in degree of penetration among four incubation temperatures. The degree of E. coli O157:H7 penetration into lettuce tissue at 4 or 22 degrees C was greater under 21% oxygen than under 2.7% oxygen; however, no difference was observed at 37 degrees C. Conditions that promote pathogen penetration into tissue could decrease the effectiveness of decontamination treatments.

Attachment of and Biofilm Formation by Enterobacter sakazakii on Stainless Steel and Enteral Feeding Tubes

“…In that study, L. monocytogenes cells were found to attach in higher numbers to the radish tissues at 20°C than at 10°C after Ն1 h of exposure. Higher numbers of E. coli O157:H7 attached to lettuce leaves at 22°C than at 4 or 10°C (54). Factors affecting attachment at different temperatures, however, may vary, depending on the nature of surfaces to which the cells are exposed.…”

Effect of temperature and chlorination of pre-washing water on shelf-life and physiological properties of ready-to-use iceberg lettuce

“…Once pathogenic bacteria have penetrated damaged tissue, their removal or destruction by normal washing is impeded . Washing lettuce with an antimicrobial solution prior to cutting may prevent transmission of pathogens to damaged tissue and therefore decrease the invasive potential (Takeuchi, Hassan, & Frank, 2001). Hence, the safety of lettuce could be enhanced by discarding damaged leaves and exposing undamaged leaves to effective levels of sanitizer before cutting, thus preventing the unwanted contamination of the damaged tissue (Seo & Frank, 1999).…”

Cold plasma inactivation of internalised bacteria and biofilms for Salmonella enterica serovar Typhimurium, Listeria monocytogenes and Escherichia coli

“…Higher temperatures and higher light intensity may induce bacterial attachment, biofilm formation and internalisation of bacterial cells in plants (Kroupitski et al, 2009;Takeuchi et al, 2001). Therefore, because consistent storage of fresh produce at the recommended temperatures of ~5°C is difficult to maintain throughout distribution (Koseki and Isobe, 2005) …”