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L. monocytogenes has been linked to fresh produce and detected in the retail environment. This study simulated the retail practices (crisping, misting, and storage) of unbagged whole heads of romaine lettuce to determine the growth of L. monocytogenes and natural psychrotrophic microflora. Three nalidixic acid-resistant strains of L. monocytogenes strains were inoculated to each head of lettuce (≈5 log10 CFU/g). For crisping, 24 heads of romaine lettuce were immersed in tap water or electrolyzed water (EW; free chlorine: 55 ppm) for 5 min, followed by holding at 5 °C for 2 h. The water-crisped (WC), EW crisped (EWC), or non-crisped (NC) lettuces were placed in a commercial refrigerated cabinet for misting at 5 °C. After 24-h misting, heads of lettuce were placed in perforated drain boxes with cover at 5 °C or 15 °C. The tap water and EW crisping achieved 1.3 and 2.9 log10 CFU/g reduction of L. monocytogenes, respectively. Approximately 1 log additional reduction of L. monocytogenes in the non-crisped lettuce was shown after misting (p < 0.05), but no significant effect of misting on the population of L. monocytogenes was observed on WC or EWC lettuces (p > 0.05). Regardless of the storage temperature or misting, L. monocytogenes populations remained significantly (p < 0.05) lower on EWC lettuce than NC and WC lettuce. On days 4 and 7 of storage, the natural psychrotrophic bacteria on lettuce stored at 5 °C was significantly lower than stored at 15 °C, and its population was not affected by crisping and misting. These provide insight into the influence of retail lettuce handling practices on the risk of L. monocytogenes. [ABSTRACT FROM AUTHOR]

Researchers demonstrate that E. coli strain O157:H7 in contaminated manure or irrigation water can enter lettuce plants and become internalized, where it would be resistant to chlorinated water used to sanitize the lettuce. This strain of E. coli has been linked to a disease called hemolytic-uremic syndrome.

Research has been conducted on the Escherichia coli O157:H7 strains. The recovery and pathogenicity of these strains stressed experimentally by long-term storage in water and chlorine exposure have been investigated, and the results are discussed.

Research reveals that vesicles shed by the gram-negative bacteria contain genetic material that can be transferred to recipient cells in which the donor genes are expressed. Data show that the genetic material also transfers virulence genes and antibiotic resistance and the transformed bacteria exhibit sixfold higher cytotoxicity.

Membrane vesicles released by Escherichia coli O157:H7 contain DNA encoding the virulence genes eae, stx1 and stx2, as well as uidA, which encodes for beta-galactosidase, while immunoblotting data show that Shiga toxins 1 and 2 are contained within vesicles. This was gleaned from a study that sought to determine whether E coli O157:H7 produces vesicles under normal growth conditions and whether these contain Shiga toxins and DNA and transfer virulent genes. Results indicate that these vesicles play a role in the export of toxic and genetic material. They can facilitate the transfer of genetic material to other enteric organisms and may serve to disseminate toxic material directly to host cells or to bacterial cells.

The efficacy of commercially available antimicrobials for fresh produce—electrolyzed water (EW; around 60 mg/L of free chlorine), a combination of lactic acid and phosphoric acid-based (LPA) and citric acid-based (CA)—was compared with tap water (TW) in preventing cross-contamination during the soaking step of crisping at a retail setting. A bunch of cilantro ((103.7±14.9) g/bunch) was inoculated with a three-strain cocktail of nalidixic acid-resistant Salmonella enterica (S. enterica) and Escherichia coli (E. coli) O157:H7, S. enterica and Listeria monocytogenes (L. monocytogenes), or E. coli O157:H7 and L. monocytogenes (around 5.0 log CFU/g). One inoculated and seven non-inoculated cilantro bunches were soaked in 76 L of TW, EW, LPA, and CA for 5 min. Two additional soakings, each with eight bunches of non-inoculated cilantro, were performed in the same soaking water. To determine the cross-contamination of inoculated foodborne pathogens via soaking water, the cilantro samples and soaking water following each soaking step were subjected to microbiological analyses using selective media supplemented with nalidixic acid (100 μg/mL). During the first soaking, significantly greater reductions in Salmonella ((2.9±0.5) log CFU/g), E. coli O157:H7 ((3.0±0.1) log CFU/g), and L. monocytogenes ((2.7±0.3) log CFU/g) on cilantro were achieved with EW compared to soaking with TW, LPA, and CA (P< 0.05). Cross-contamination of foodborne pathogens from inoculated cilantro to non-inoculated cilantro was completely mitigated by EW during three subsequent soaking events. With the exception of TW soaking water, no inoculated foodborne pathogens were detected in the 100 mL soaking water of EW, CA, and LPA collected. Including an appropriate concentration of chemical antimicrobial in water during the soaking step of crisping aids in mitigating cross-contamination of foodborne pathogen(s) in cilantro bunches. [ABSTRACT FROM AUTHOR]

The use of human antibiotics in agriculture as well as in poultry, beef and pigs, is on the rise in the US, making scientists worry that by this sharing of antibiotics the drug will be ineffective in humans. However the US government is taking a series of measures to counter this.