Transcriptional responses of Escherichia coli K-12 and O157:H7 associated with lettuce leaves.

An increasing number of outbreaks of gastroenteritis recently caused by Escherichia coli O157:H7 have been linked to the consumption of leafy green vegetables. Although it is known that E. coli survives and grows in the phyllosphere of lettuce plants, the molecular mechanisms by which this bacterium associates with plants are largely unknown. The goal of this study was to identify E. coli genes relevant to its interaction, survival, or attachment to lettuce leaf surfaces, comparing E. coli K-12, a model system, and E. coli O157:H7, a pathogen associated with a large number of outbreaks. Using microarrays, we found that upon interaction with intact leaves, 10.1% and 8.7% of the 3,798 shared genes were differentially expressed in K-12 and O157:H7, respectively, whereas 3.1% changed transcript levels in both. The largest group of genes downregulated consisted of those involved in energy metabolism, including tnaA (33-fold change), encoding a tryptophanase that converts tryptophan into indole. Genes involved in biofilm modulation (bhsA and ybiM) and curli production (csgA and csgB) were significantly upregulated in E. coli K-12 and O157:H7. Both csgA and bhsA (ycfR) mutants were impaired in the long-term colonization of the leaf surface, but only csgA mutants had diminished ability in short-term attachment experiments. Our data suggested that the interaction of E. coli K-12 and O157:H7 with undamaged lettuce leaves likely is initiated via attachment to the leaf surface using curli fibers, a downward shift in their metabolism, and the suppression of biofilm formation.

Inactivation of SARS-CoV-2 by 2 commercially available Benzalkonium chloride-based hand sanitizers in comparison with an 80% ethanol-based hand sanitizer.

BACKGROUND: The CDC and WHO recommend alcohol-based hand sanitizers to inactivate severe acute respiratory syndrome coronavirus-2 [SARS-CoV-2]. AIM: Benzalkonium chloride [BAK] is another hand sanitizer active ingredient that could be used in response to the global pandemic. Deployment of BAK-based hand sanitizers could reduce shortages of alcohol products and increase hand hygiene options where there are social, physical, and toxicological constraints on alcohol use. METHODS: Two commercially available BAK-based hand sanitizers, a concentrate diluted on-site with water and a ready-to-use product, were tested for activity against SARS-CoV-2 in the European Norm Virucidal Activity Suspension Test [EN14476]. A WHO and CDC-recommended 80% alcohol-based hand sanitizer formulation was tested in parallel. FINDINGS: Both BAK formulations demonstrated a ≥4.0 log10 reduction of SARS-CoV-2 in 30 seconds, meeting the EN14476 performance standard for virucidal activity against SARS-CoV-2 and matching the in vitro effectiveness of the ethanol-based sanitizer. CONCLUSION: These findings indicate that a commercial BAK hand hygiene formulation may be another effective means of inactivating the SARS-CoV-2 virus and could be considered as option for pandemic response.

Viral Inactivation in Foods: A Review of Traditional and Novel Food-Processing Technologies.

Over one-half of foodborne illnesses are believed to be viral in origin. The ability of viruses to persist in the environment and foods, coupled with low infectious doses, allows even a small amount of contamination to cause serious problems. An increased incidence of foodborne illnesses and consumer demand for fresh, convenient, and safe foods have prompted research into alternative food-processing technologies. This review focuses on viral inactivation by both traditional processing technologies such as use of antimicrobial agents and the application of heat, and also novel processing technologies including high-pressure processing, ultraviolet- and gamma-irradiation, and pulsed electric fields. These industrially applicable control measures will be discussed in relation to the 2 most common causes of foodborne viral illnesses, hepatitis A virus and human noroviruses. Other enteric viruses, including adenoviruses, rotaviruses, aichi virus, and laboratory and industrial viral surrogates such as feline caliciviruses, murine noroviruses, bacteriophage MS2 and ΦX174, and virus-like particles are also discussed. The basis of each technology, inactivation efficacy, proposed mechanisms of viral inactivation, factors affecting viral inactivation, and applicability to the food industry with a focus on ready-to-eat foods, produce, and shellfish, are all featured in this review.

Factors influencing germination of Bacillus subtilis spores via activation of nutrient receptors by high pressure.

Different nutrient receptors varied in triggering germination of Bacillus subtilis spores with a pressure of 150 MPa, the GerA receptor being more responsive than the GerB receptor and even more responsive than the GerK receptor. This hierarchy in receptor responsiveness to pressure was the same as receptor responsiveness to a mixture of nutrients. The levels of nutrient receptors influenced rates of pressure germination, since the GerA receptor is more abundant than the GerB receptor and elevated levels of individual receptors increased spore germination by 150 MPa of pressure. However, GerB receptor variants with relaxed specificity for nutrient germinants responded as well as the GerA receptor to this pressure. Spores lacking dipicolinic acid did not germinate with this pressure, and pressure activation of the GerA receptor required covalent addition of diacylglycerol. However, pressure activation of the GerB and GerK receptors displayed only a partial (GerB) or no (GerK) diacylglycerylation requirement. These effects of receptor diacylglycerylation on pressure germination are similar to those on nutrient germination. Wild-type spores prepared at higher temperatures germinated more rapidly with a pressure of 150 MPa than spores prepared at lower temperatures; this was also true for spores with only one receptor, but receptor levels did not increase in spores made at higher temperatures. Changes in inner membrane unsaturated fatty acid levels, lethal treatment with oxidizing agents, or exposure to chemicals that inhibit nutrient germination had no major effect on spore germination by 150 MPa of pressure, except for strong inhibition by HgCl2.