Antimicrobial Resistance in Salmonella Isolated from Food Workers and Chicken Products in Japan.

Salmonella is an enteric bacterial pathogen that causes foodborne illness in humans. Third-generation cephalosporin (TGC) resistance in Salmonella remains a global concern. Food workers may represent a reservoir of Salmonella, thus potentially contaminating food products. Therefore, we aimed to investigate the prevalence of Salmonella in food workers and characterize the isolates by serotyping and antimicrobial susceptibility testing. Salmonella was isolated from 583 (0.079%) of 740,635 stool samples collected from food workers between January and December 2018, and then serotyped into 76 Salmonella enterica serovars and 22 untypeable Salmonella strains. High rates of antimicrobial resistance were observed for streptomycin (51.1%), tetracycline (33.1%), and kanamycin (18.4%). Although isolates were susceptible to ciprofloxacin, 12 (2.1%) strains (one S. Infantis, one S. Manhattan, two S. Bareilly, two S. Blockley, two S. Heidelberg, two S. Minnesota, one S. Goldcoast, and one untypeable Salmonella strain) were resistant to the TGC cefotaxime, all of which harbored ß-lactamase genes (blaCMY-2, blaCTX-M-15, blaCTX-M-55, and blaTEM-52B). Moreover, 1.3% (4/309) of Salmonella strains (three S. Infantis and one S. Manhattan strains) isolated from chicken products were resistant to cefotaxime and harbored blaCMY-2 or blaTEM-52B. Thus, food workers may acquire TGC-resistant Salmonella after the ingestion of contaminated chicken products and further contaminate food products.

[Detection of enteric pathogen bacteria with the PCR method from mixed fecal specimens of food handlers].

We developed an assay for rapid, specific detection of Shigella, Salmonella, and verotoxin-producing Escherichia coli O157 using the direct PCR analysis of mixed human fecal specimens. In this study, the sensitivity of the direct PCR assay for 50 mixed human fecal specimen was found to be 1.3, 0.42, and 0.76 colony-forming units/kit for Shigella sonnei, Salmonella Typhimurium, and verotoxin-producing E. coli O157, respectively. We compared the efficiency of the direct PCR method with the conventional direct agar plate method for 5000 fecal specimens from food handlers. The 50 mixed fecal specimens were concentrated to approximately 2.5% in distilled water and were heated to 95 degrees C for 5min. Then, 5 µL of the specimen supernatant was added to 45 µL of the PCR mixture. Direct PCR results were evaluated by melting curve analysis. Among the 5000 fecal specimens from food handlers, Salmonella Infantis was isolated from 1 specimen using the direct agar plate method, and it was positive for the Salmonella gene (stn), as confirmed with the direct PCR method. Shigella, Salmonella, or verotoxin-producing E. coli O157 were not detected in the remaining 4999 fecal specimens with the direct agar plate method. However, Salmonella Enteritidis isolated by the enrichment culture method from 1 fecal specimen was positive for stn. Non-O157 verotoxin-producing E. coli isolated using direct horse blood agar from another fecal specimen was positive for stx. Moreover, enteroinvasive E. coli isolated using direct BTB agar from one fecal specimen was positive for ipaH. We conclude that the direct PCR assay can be applied as a new rapid screening method for personal hygiene among food handlers.

[Direct PCR detection of food-borne bacteria from mixed human feces].

Mixed human feces were evaluated for simultaneous direct PCR detection of 3 food-borne bacteria--verotoxin-producing bacteria, Salmonella, and Shigella. Mixed feces concentrated approximately 2.5% in distilled water, were heated at 95 degrees C for 5 min. The heated suspension was then centrifuged and 5 microL of the supernatant poured into a 45 microL PCR mixture prepared to neutralize PCR inhibitors originating in biological samples. As a result of PCR under the above conditions followed by melting curve analysis (MCA), one positive fecal sample containing food-borne bacteria was detected from among 50 mixed fecal samples, showing the same sensitivity as individual cultivation. Results thus indicate that this method enables rapid, reliable, highly sensitive testing of many fecal samples--especially those of personnel handling food, which requires the simultaneous testing of many samples.