The secondary contamination during/after cooking is one of the causes of food poisoning. In order to prevent the occurrence of such incidents, it is necessary to identify locations where microorganisms are likely to adhere in food manufacturing facilities, and to efficiently remove them. In this study, we obtained aerobic plate count of 22 locations in a university’s food manufacturing training room in a total of 9 times to identify locations where microorganisms are likely to adhere. The median number of bacteria was 1.78 log cfu/100 cm² on the flat surface, while it was 2.12 log cfu/100 cm² on the handle, confirming that the number of bacteria on the handle was significantly higher (p < 0.05). Next, amplicon analysis was performed on the blast chiller handle where the highest number of viable bacteria was detected, and the contamination route was clarified. It was suggested that the bacteria that had been attached to the bean seedlings and sprouts may have been transmitted by the hands and attached to the handles. Finally, we investigated the effects of slightly acidic electrolyzed water used for cleaning manufacturing equipment. The log reduction value for the wiping solution was 0.098 to 0.31 log cfu, whereas that for isolated bacteria of the solution was 3.9 to 4.2 log cfu, suggesting the presence of a substance in the wiping solution that inhibits the action of electrolyzed water. These results suggest that it is desirable to monitor the sanitary conditions of handles, and to perform two-step cleaning using electrolyzed water, in order to prevent secondary contamination.

Selective broths for Escherichia albertii have been developed for its selective enrichment and efficient isolation. Here, we evaluated E. albertii-selective media, CTD-TSB and NCT-mTSB, for the efficiency of detection and isolation using wild raccoon fecal specimens. CTD-TSB culture yielded comparable detection rate (71.5%) to and higher isolation rate (34.3%) than non-selective enrichment with TSB (71.4% and 5.0%, respectively). While detection rate of NCT-mTSB culture was lower (55.6%) than the other broths, it yielded much higher isolation rate (79.8%). PCR-based intra-specimen diversity analysis of E. albertii isolates identified 2 or more genotypes in 38.7% of raccoon specimens from which this bacterium was isolated. Both the selective broths contributed to catching the heterogeneic E. albertii from each specimen as well as increasing the isolation efficiency. However, in several raccoon specimens, certain E. albertii genotypes identified in non-enriched samples were not identified when selective enrichment broths were used, especially in the NCT-mTSB. The discrepancies were more noticeable in specimens with low E. albertii load, where it could not be detected without prior enrichment. Growth test with selected isolates revealed that the bacterial load required for successful growth in NCT-mTSB varied significantly among isolates (10¹ to 10⁷ CFU). Some isolates which could not be isolated from NCT-mTSB required more E. albertii to grow in this medium than number of E. albertii initially present in the fecal samples, suggesting that they were not isolated from selective broths because their numbers were low. These findings suggest that combination of at least two media for enrichment is necessary to avoid false-negative results and for comprehensive isolations.

We conducted an epidemiological analysis of bacteriological test results (N = 44,218) from hand swabs collected after hand washing from 2017 to 2023 to understand the hand hygiene practices of food handlers at work and assess the impact of routine hand sanitization during the COVID-19 pandemic. The Mean and standard deviation of standard plate count (SPC) was 2.70±1.01 log10 CFU per swab, with coliform (CF) and Staphylococcus aureus (SA) positive rates at 2.24% and 4.22%, respectively. Swabs collected from gloves worn by food handlers showed significantly lower SPC than those collected from bare hands. Positive rates for CF and SA were higher in cases involving “long nails” and “wounds or rough hands,” respectively. Mean SPC values were higher in swabs from CF- or SA-positive cases than in swabs from negative cases. Variations in the mean SPC values and positive rates for CF and SA were observed across different categories of food facilities. Both the mean SPC values and positive rates for CF and SA increased during the summer months (July to September). The mean SPC values and CF-positive rates decreased during the COVID-19 pandemic, whereas the SA-positive rates increased. In a laboratory experiment assessing various hand hygiene methods after handling foodstuffs naturally contaminated with microorganisms, “hand rubbing with alcohol” was found to be the most effective, followed by “adequate hand washing” and “inadequate hand washing.” The log reduction in SPC was greater for individuals working as sanitation inspectors who were highly experienced in hand washing than for others. The mean SPC values and distribution for “adequate hand washing” were similar to those observed in food handlers after hand washing. These findings provide valuable scientific data for hand hygiene instruction.