Effect of Food Residues on Norovirus Survival on Stainless Steel Surfaces

Background: In households and food processing plants, minute food residues left behind from improper cleaning may influence the survivability of human norovirus on surfaces. In this study, the survivability of norovirus on desiccated food residue-attached stainless steel coupons was investigated. Methodology/Principal Findings: Using murine norovirus-1 (MNV-1) as a surrogate of human norovirus, the survivability of norovirus was investigated on lettuce, cabbage, or ground pork-attached stainless steel coupons. A 6.2 log MPN/ml of MNV-1 infectivity was completely lost at day 30 in residue-free coupons, whereas only a 1.4 log MPN/ml reduction was observed in coupons with residues. Moreover, the disinfective effect of sodium hypochlorite was reduced when residues were present on the coupons. Conclusions/Significance: This study revealed that the food residues increased the survivability and the resistance to chemicals of norovirus, indicating the need of thorough cleaning in food processing plants and household settings

Risk of Listeria monocytogenes Contamination of Raw Ready-To-Eat Seafood Products Available at Retail Outlets in Japan▿

Examination of Listeria monocytogenes prevalence among ready-to-eat foods in Japan revealed frequent (5.7 to 12.1%) contamination of minced tuna and fish roe products, and the isolates had the same virulence levels as clinical isolates in terms of invasion efficiency and infectivity in cell cultures and a murine infection model, respectively. Premature stop codons in inlA were infrequent (1 out of 39 isolates). Cell numbers of L. monocytogenes in minced tuna and salmon roe increased rapidly under inappropriate storage temperatures (from a most probable number [MPN] of 100 to 101/g to an MPN of 103 to 104/g over the course of 2 days at 10°C). Thus, regulatory guidelines are needed for acceptable levels of L. monocytogenes in these foods

Reduction of MNV-1 on stainless steel coupons by sodium hypochlorite.

<p>Stainless steel coupons with or without food residues were exposed for 5 min to various concentration of sodium hypochlorite at room temperature. Error bars indicate standard deviations obtained from three independent experiments.</p

Survival of MNV-1 on stainless steel coupons with or without food residues.

<p>Food residue (cabbage, ground pork, or lettuce) -attached stainless steel coupons and coupons without any food component were incubated at 25°C over a 7-day experimental period. Error bars indicate standard deviations obtained from three independent experiments.</p

A dendrogram based on MLTSA and MVLST.

<p>The dendrogram is based on nucleotide sequences in 3 multilocus tandem-repeat sequence analysis (MLTSA) regions (regions 1, 2, and 3) and 6 multi-virulence-locus sequence typing (MVLST) regions. Epidemic clone groupings are shown to the right of the isolates. JF: Japanese food isolate, JC: Japanese clinical isolate.</p

Allelic diversities of MLTSA with 3 regions and MVLST with 6 regions.

<p>Allelic diversities of MLTSA with 3 regions and MVLST with 6 regions.</p

Genetic Characteristics of Japanese Clinical <i>Listeria monocytogenes</i> Isolates

<div><p><i>Listeria monocytogenes</i> causes foodborne illnesses through consumption of ready-to-eat foods. Although 135-201annual listeriosis cases have been estimated in Japan, the details regarding the clinical isolates such as infection source, virulence level, and other genetic characteristics, are not known. In order to uncover the trends of listeriosis in Japan and use the knowledge for prevention measures to be taken, the genetic characteristics of the past human clinical isolates needs to be elucidated. For this purpose, multilocus tandem-repeat sequence analysis (MLTSA) and multi-virulence-locus sequence typing (MVLST) were used in this study. The clinical isolates showed a variety of genetically distant genotypes, indicating they were from sporadic cases. However, the MVLST profiles of 7 clinical isolates were identical to those of epidemic clone (EC) I isolates, which have caused several serious outbreaks in other countries, suggesting the possibility that they have strong virulence potential and originated from a single outbreak. Moreover, 6 Japanese food isolates shared their genotypes with ECI isolates, indicating that there may be risks for listeriosis outbreak in Japan. This is the first investigational study on genetic characteristics of Japanese listeriosis isolates. The listeriosis cases happened in the past are presumably sporadic, but it is still possible that some isolates with strong virulence potential have caused listeriosis outbreaks, and future listeriosis risks also exist.</p></div