Isolation of Shiga Toxin-Producing Escherichia coli from the Surfaces of Beef Carcasses in Slaughterhouses in Japan

Shiga toxin-producing E. coli (STEC) is an important foodborne pathogen worldwide. It is necessary to control and prevent STEC contamination on beef carcasses in slaughterhouses because STEC infection is associated with beef consumption. However, the frequencies of STEC contamination of beef carcasses in various slaughterhouses in Japan are not well known. Herein, we investigated the contamination of beef carcasses with STEC in slaughterhouses to assess the potential risks of STEC. In total, 524 gauze samples were collected from the surfaces of beef carcasses at 12 domestic slaughterhouses from November 2020 to February 2023. The samples were measured for aerobic plate counts and tested for pathogenic genes (stx and eae) and major O-serogroups (O26, O45, O103, O111, O121, O145, and O157) by real-time PCR screening. Subsequently, immunomagnetic separation (IMS) was performed on samples positive for stx, eae, and at least one of the seven O-serogroups of STEC. Isolation process without IMS was performed on samples positive for stx, including those subjected to IMS. STEC O157:H7 and stx-positive E. coli other than serotype O157:H7 were isolated from 0.6% and 4.6% of beef carcass surfaces, respectively. Although the STEC O157:H7 isolation rate was low and stx-positive E. coli other than serotype O157:H7 belonged to minor O-serogroups, the results mean a risk of foodborne illness. Furthermore, a moderate correlation was observed between aerobic plate counts and detection rates of stx-positive samples by real-time PCR screening. The STEC O157:H7 isolated facilities showed higher values on aerobic plate counts and detection rates of stx-positive samples than the mean values of total samples. Therefore, these results suggest that it is important to evaluate hygiene treatments against beef carcasses for the reduction of STEC contamination risk, particularly in facilities with high aerobic plate counts.

An interlaboratory study on the detection method for Escherichia albertii in food using real time PCR assay and selective agars

Escherichia albertii is an emerging enteropathogen. Although E. albertii-specific detection and isolation methods have been developed, their efficiency on food samples have not yet been systematically studied. To establish a series of effective methods for detecting E. albertii in food, an interlaboratory study was conducted in 11 laboratories using enrichment with modified E. coli broth supplemented with cefixime and tellurite (CT-mEC), real-time PCR assay, and plating on four kinds of selective agars. This study focused on the detection efficiency of an E. albertii-specific real-time PCR assay (EA-rtPCR) and plating on deoxycholate hydrogen sulfide lactose agar (DHL), MacConkey agar (MAC), DHL supplemented with rhamnose and xylose (RX-DHL), and MAC supplemented with rhamnose and xylose (RX-MAC). Chicken and bean sprout samples were inoculated with E. albertii either at 17.7 CFU/25 g (low inoculation level) or 88.5 CFU/25 g (high inoculation level), and uninoculated samples were used as controls. The sensitivity of EA-rtPCR was 1.000 for chicken and bean sprout samples inoculated with E. albertii at low and high inoculation levels. The Ct values of bean sprout samples were higher than those of the chicken samples. Analysis of microbial distribution by 16S rRNA gene amplicon sequencing in enriched cultures of bean sprout samples showed that approximately >96 % of the population comprised unidentified genus of family Enterobacteriaceae and genus Acinetobacter in samples which E. albertii was not isolated. The sensitivity of the plating methods for chicken and bean sprout samples inoculated with a high inoculation level of E. albertii was 1.000 and 0.848-0.970, respectively. The sensitivity of the plating methods for chicken and bean sprout samples inoculated with a low inoculation level of E. albertii was 0.939-1.000 and 0.515-0.727, respectively. The E. albertii-positive rate in all colonies isolated in this study was 89-90 % in RX-DHL and RX-MAC, and 64 and 44 % in DHL and MAC, respectively. Therefore, the sensitivity of RX-supplemented agar was higher than that of the agars without these sugars. Using a combination of enrichment in CT-mEC and E. albertii isolation on selective agars supplemented with RX, E. albertii at an inoculation level of over 17.5 CFU/25 g of food was detected with a sensitivity of 1.000 and 0.667-0.727 in chicken and bean sprouts, respectively. Therefore, screening for E. albertii-specific genes using EA-rtPCR followed by isolation with RX-DHL or RX-MAC is an efficient method for E. albertii detection in food.

Growth and Survival of Escherichia albertii in Food and Environmental Water at Various Temperatures

Escherichia albertii is an emerging foodborne pathogen that causes diarrhea. E. albertii has been isolated from various foods, including pork and chicken meat, and environmental waters, such as river water. Although many food poisoning cases have been reported, there have been insufficient analyses of bacterial population behaviors in food and environmental water. In this study, we inoculated 2-5 log CFU of E. albertii into 25 g of pork, chicken meat, Japanese rock oyster, Pacific oyster, and 300 mL of well water and seawater at 4°C, 10°C, 20°C, and 30°C, and analyzed the bacterial population behavior in food and environmental water. After 3 days at 4°C, the population of E. albertii strain EA21 and EA24 in foods maintained approximately 4 log CFU/25 g. After 3 days at 10°C, the population of E. albertii strains in pork and oysters maintained approximately 4 log CFU/25 g, and that in chicken meat increased to approximately 5-6 log CFU/25 g. After 2 days at 20°C, E. albertii strains grew to approximately 6-7 log CFU/25 g in pork and chicken meat, and E. albertii strain EA21 but not EA24 grew to 4.5 log CFU/25 g in Japanese rock oyster, E. albertii strain EA21 but not EA24 slightly grew to 3.1 log CFU/25 g in Pacific oyster. After 1 day at 30°C, E. albertii strains grew to approximately 7-8 log CFU/25 g in chicken meat and pork, grew to approximately 4-6 log CFU/25 g in Japanese rock oyster, and 6-7 log CFU/25 g in Pacific oyster. These results suggest that E. albertii survives without growth below 4°C and grew rapidly at 20°C and 30°C in foods, especially in meat. E. albertii strains did not grow in well water and seawater at 4°C, 10°C, 20°C, and 30°C. The population of E. albertii strains in well water and seawater decreased faster at 30°C than at 4°C, 10°C, and 20°C, suggesting that E. albertii has low viability at 30°C in environmental water.

An experimental verification of fungal overgrowth in temporary houses at the site of the Great East Japan Earthquake

Fungal contamination in the indoor air of prefabricated temporary houses at the site of the Great East Japan Earthquake revealed extremely high levels compared to those found in conventional residences. We experimentally investigated fungal growth levels on different interior materials to support fungal overgrowth in prefabricated temporary houses. Three species each of allergenic fungi and invasive fungi observed in temporary housing were selected for inoculation tests with various interior materials. The experiments with fungal inoculation were conducted in conformance with standards for industrial products described in the Japanese" JIS Z 2911:2018 Methods of test for fungus resistance" with small modifications. After incubation, visual and stereomicroscopic assessments were performed to determine fungal growth levels. The viability of the fungi varied according to the interior material type. Our findings demonstrate the importance of antifungal measures in indoor environments and the need for additional research on the growth levels of fungal species on various interior materials.

Atypical diarrhoeagenic Escherichia coli in milk related to a large foodborne outbreak

A foodborne outbreak related to milk cartons served in school lunches occurred in June 2021, which involved more than 1,800 cases from 25 schools. The major symptoms were abdominal pain, diarrhoea, vomiting, and fever. Although major foodborne toxins and pathogens were not detected, a specific Escherichia coli strain, serotype OUT (OgGp9):H18, was predominantly isolated from milk samples related to the outbreak and most patients tested. The strains from milk and patient stool samples were identified as the same clone by core genome multilocus sequence typing and single-nucleotide polymorphism analysis. The strain was detected in milk samples served for two days related to the foodborne outbreak at a rate of 69.6% and levels of less than ten most probable number/100 mL but not on days unrelated to the outbreak. The acid tolerance of the strain for survival in the stomach was similar to that of enterohaemorrhagic E. coli O157:H7, and the same inserts in the chu gene cluster in the acid fitness island were genetically revealed. The pathogenicity of the strain was not clear; however, it was indicated that the causative pathogen was atypical diarrhoeagenic E. coli OUT (OgGp9):H18.

Development of detection methods by multiplex real-time PCR for highly pathogenic Yersinia enterocolitica, low pathogenic Yersinia enterocolitica, and Yersinia pseudotuberculosis based on SYBR green and TaqMan probes

This study aimed to develop multiplex real-time PCR methods using SYBR Green and TaqMan probes for rapid and sensitive diagnosis, differentiating three pathogenic Yersinia groups such as highly pathogenic Y. enterocolitica, low pathogenic Y. enterocolitica, and Y. pseudotuberculosis. Specific primer and probe combinations for differentiating three pathogenic Yersinia groups were designed from three chromosomally encoded genes (ail, fyuA, and inv). Twenty-six stains of pathogenic Yersinia species including 6 strains of low pathogenic Y. enterocolitica serotypes, 7 strains of highly pathogenic Y. enterocolitica serotypes, and 13 strains of pathogenic Y. pseudotuberculosis were used for specificity testing. Specific patterns of real-time amplification signals distinguished three pathogenic Yersinia groups. A detection limit of approximately 10¹ colony forming units (CFU) /reaction of genomic DNA was determined based on plate counts. Furthermore, the multiplex real-time PCR methods also detected Y. enterocolitica O:8 from the DNA extracted from spiked rabbit blood samples and potentially infected wild rodent fecal samples. These results demonstrated that the multiplex real-time PCR methods developed in this study are useful for rapid detection and differentiation of three pathogenic Yersinia groups. Therefore, these methods provide a new monitoring and detection capability to understand the epidemiology of pathogenic Yersinia and to diagnose three pathogenic Yersinia groups.

Prevalence and abundance of Anisakis larvae in ready-to-eat mackerel products in Japan

The risk of contracting anisakiasis from consuming ready-to-eat (RTE) mackerel products in Japan was investigated by examining the prevalence and abundance of Anisakis simplex and its sibling species in these products. From 2019 to 2021, a total of 448 RTE mackerel products were purchased in Japan. Anisakis larvae were isolated from 244 of the 448 samples (54 %), and live larvae were isolated from 161 of the 448 samples (36 %). In total, 3170 Anisakis larvae, which included 919 live larvae, were isolated. The isolated Anisakis larvae consisted of 3118 A. simplex (s. s.), 27 A. pegreffii, and 25 hybrid genotype (A. simplex [s. s.] × A. pegreffii) larvae. No A. berlandi larvae were isolated. The prevalence of larvae in samples of mackerel caught in the Southern Japan region and Sea of Japan was much lower than that in mackerel caught in other areas. Both the prevalence of Anisakis larvae in all samples and their abundance in larvae-positive samples exhibited specific seasonal variations, being high in spring.

Determination of the biological origin of enzyme preparations using SDS-PAGE and peptide mass fingerprinting

Enzymes are mainly extracted from the culture broth of microorganisms. Various commercially available enzyme preparations (EPs) are derived from different microorganisms, and the source of the EP should be the same as that mentioned in the manufacture's information. The development of analytical methods that can determine the origin of the final products is important for ensuring that the EPs are nontoxic, especially when used as food additives. In this study, various EPs were subjected to SDS-PAGE, and the main protein bands were excised. After in-gel digestion, the generated peptides were analysed using MALDI-TOF MS, and protein identification was performed by searching the set of peptide masses against protein databases. In total, 36 EPs including amylase, β-galactosidase, cellulase, hemicellulase and protease were analysed, and the information about the enzyme sources was obtained for 30 EPs. Among these, the biological sources determined for 25 EPs were consistent with the manufacturer's information; for the remaining five, enzymes produced by closely-related species were shown as matching proteins due to high sequence similarity. Six enzymes derived from four microorganisms could not be identified because their protein sequences were not registered in the database. As these databases are expanded, this approach of using SDS-PAGE and peptide mass fingerprinting (PMF) can determine the biological origin of enzymes rapidly and contribute to ensuring the safety of EPs.

Antimicrobial resistance profiles of Campylobacter jejuni and Salmonella spp. isolated from enteritis patients in Japan

Understanding the antimicrobial resistance of Campylobacter jejuni and Salmonella spp. isolated from patients with enteritis will aid in therapeutic decision-making. This study aimed to characterize C. jejuni and Salmonella spp. isolates from patients with enteritis. For C. jejuni, the resistance rates against ampicillin, tetracycline, and ciprofloxacin were 17.2%, 23.8%, and 46.4%, respectively. All the C. jejuni isolates were susceptible to erythromycin, which is recommended as a first-choice antimicrobial if Campylobacter enteritis is strongly suspected. C. jejuni was classified into 64 sequence types (STs), and the five major STs were ST22, ST354, ST21, ST918, and ST50. The ciprofloxacin-resistance rate of ST22 was 85.7%. For Salmonella, the resistance rates against ampicillin, cefotaxime, streptomycin, kanamycin, tetracycline, and nalidixic acid were 14.7%, 2.0%, 57.8%, 10.8%, 16.7%, and 11.8%, respectively. All the Salmonella spp. isolates were susceptible to ciprofloxacin. Therefore, fluoroquinolones are the recommended antimicrobials against Salmonella enteritis. S. Thompson, S. Enteritidis, and S. Schwarzengrund were the three most prevalent serotypes. The two cefotaxime-resistant isolates were serotyped as S. Typhimurium and were found to harbor bla_CMY-2. The results of this study would help select antimicrobials for treating patients with Campylobacter and Salmonella enteritis.

[Suitability of Culture Broth and Conditions for Escherichia coli Growth and Gas Production as a Test for Food Additives in EC Broth]

The growth and gas production test for Escherichia coli in the microbiological examination of food additives is stipulated in the ninth edition of Japan's Specifications and Standards for Food Additives (JSFA) and described as a part of the "Confirmation Test for Escherichia coli" in "Microbial Limit Tests" in the same manuscript. The growth and gas production test for E. coli indicated that the positive or negative of "gas production and/or turbidity" in EC broth should be confirmed after incubating at 45.5±0.2℃ for 24±2 h. If both gas production and turbidity are negative, the culture is additionally incubated up to 48±2 h to determine E. coli contamination. The internationally referenced Bacteriological Analytical Manual of the U.S. FDA had revised the incubation temperature in tests for coliforms and E. coli from 45.5±0.2℃ to 44.5±0.2℃ in 2017. Therefore, we conducted research in anticipation of this temperature change being reflected in the microbiological examination of the JSFA. We used seven EC broth products and six food additives across eight products that are available in Japan in order to compare the growth and gas production at temperatures of 45.5±0.2℃ and 44.5±0.2℃ of E. coli NBRC 3972, which is designated as the test strain in JSFA. Both with/without food additives, the number of EC broth products in which medium turbidity and gas production by the strain were positive in three out of three tubes at all test times was greater at 44.5±0.2℃ than at 45.5±0.2℃. These results suggest that the growth and gas production test for E. coli could be more appropriately conducted by incubation at 44.5±0.2℃ in the "Confirmation Test for Escherichia coli" for E. coli in the JSFA in comparison to 45.5±0.2℃. Furthermore, there were differences in the growth and gas production of E. coli NBRC 3972 depending on the EC broth product used. Therefore, the importance of "Media growth promotion test" and "Method suitability test" in the ninth edition of the JSFA should be emphasized.

Development of a Novel Real-Time Polymerase Chain Reaction Assay to Detect Escherichia albertii in Chicken Meat

Escherichia albertii is an emerging enteropathogen. Several foodborne outbreaks of E. albertii have been reported in Japan; however, foods associated with most outbreaks remain unidentified. Therefore, polymerase chain reaction (PCR) assays detecting E. albertii specifically and sensitively are required. Primers and probe for real-time PCR assays targeting E. albertii-specific gene (EA-rtPCR) was designed. With 74 strains, including 43 E. albertii strains and several of its close relatives, EA-rtPCR specifically amplified E. albertii; therefore, the sensitivity of EA-rtPCR was then evaluated. The detection limits were 2.8 and 2.0-3.2 log colony-forming unit (CFU)/mL for E. albertii culture and enriched chicken culture inoculated with the pathogen, respectively. In addition, E. albertii was detected from 25 g of chicken meat inoculated with 0.1 log CFU of the pathogen by EA-rtPCR. The detection of E. albertii from chicken meat by EA-rtPCR was also evaluated by comparing with the nested-PCR assay, and 28 retail chicken meat and 193 dissected body parts from 21 chicken carcass were tested. One and three chicken meat were positive in the nested-PCR assay and EA-rtPCR, respectively. Fourteen carcasses had at least one body part that was positive for EA-rtPCR, and 36 and 48 samples were positive for the nested-PCR assay and EA-rtPCR, respectively. A total of 37 strains of E. albertii were isolated from seven PCR-positive samples obtained from six chicken carcass. All E. albertii isolates harbored eae gene, and were classified as E. albertii O-genotype (EAOg)3 or EAOg4 by EAO-genotyping. The EA-rtPCR developed in this study has potential to improve E. albertii detection in food and advance research on E. albertii infection.

Cross-genus inhibitory activity of polyoxins against aflatoxin production by Aspergillus parasiticus and fumonisin production by Fusarium fujikuroi

Co-exposure to aflatoxin and fumonisin is a health concern where corn is a staple food, and a method to prevent co-contamination of these mycotoxins in foods is urgently needed. Polyoxins are chitin synthase inhibitors produced by Streptomyces cacaoi var. asoensis. The aflatoxin production inhibitory activity of a commercially available polyoxin D and four polyoxins purified from polyoxin AL water-soluble powder, an agricultural chemical containing polyoxins, was tested. The five polyoxins dose-dependently inhibited aflatoxin production by Aspergillus parasiticus and the IC50 values of polyoxin A, B, D, K and L were 16, 74, 110, 9 and 280 µmol L-1, respectively. Polyoxins also inhibited fumonisin production by Fusarium fujikuroi, and the IC50 values of polyoxin B, D, K and L were 270, 42, 65 and 62 µmol L-1, respectively. Polyoxins repressed the transcription of genes encoding proteins required for aflatoxin biosynthesis in A. parasiticus and fumonisin biosynthesis in F. fujikuroi. Polyoxin K and D also inhibited conidiation in A. parasiticus and F. fujikuroi, respectively. These results suggest that a mixture of polyoxins may effectively prevent co-contamination of aflatoxin and fumonisin in foods.

Matrix-Assisted Laser Desorption and Ionization Time-of-Flight Mass Spectrometry Analysis for the Direct Detection of SARS-CoV-2 in Nasopharyngeal Swabs

The most common diagnostic method used for coronavirus disease-2019 (COVID-19) is real-time reverse transcription polymerase chain reaction (PCR). However, it requires complex and labor-intensive procedures and involves excessive positive results derived from viral debris. We developed a method for the direct detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in nasopharyngeal swabs, which uses matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-ToF MS) to identify specific peptides from the SARS-CoV-2 nucleocapsid phosphoprotein (NP). SARS-CoV-2 viral particles were separated from biological molecules in nasopharyngeal swabs by an ultrafiltration cartridge. Further purification was performed by an anion exchange resin, and purified NP was digested into peptides using trypsin. The peptides from SARS-CoV-2 that were inoculated into nasopharyngeal swabs were detected by MALDI-ToF MS, and the limit of detection was 10^6.7 viral copies. This value equates to 10^7.9 viral copies per swab and is approximately equivalent to the viral load of contagious patients. Seven NP-derived peptides were selected as the target molecules for the detection of SARS-CoV-2 in clinical specimens. The method detected between two and seven NP-derived peptides in 19 nasopharyngeal swab specimens from contagious COVID-19 patients. These peptides were not detected in four specimens in which SARS-CoV-2 RNA was not detected by PCR. Mutated NP-derived peptides were found in some specimens, and their patterns of amino acid replacement were estimated by accurate mass. Our results provide evidence that the developed MALDI-ToF MS-based method in a combination of straightforward purification steps and a rapid detection step directly detect SARS-CoV-2-specific peptides in nasopharyngeal swabs and can be a reliable high-throughput diagnostic method for COVID-19.

[Literature Review on the Type of Fish and Histamine-producing Bacteria Associated with Histamine Poisonings in Japan]

Histamine poisoning has been reported worldwide. Improvements in refrigeration technology have led to a reduction in this food poisoning; however, it continues to occur. Misdiagnosis of fish allergies has compounded this problem and the number of patients subjected to histamine poisoning that are transported to the emergency ward because of anaphylactic shock-like symptoms should not be underestimated. We investigated incidents of histamine food poisoning in Japan from 1998 to 2020, and found that there were a mean 9.7 incidents/year and 195.3 cases/year. Facility-wise occurrence of the incidents per year was the highest in restaurants followed by lunch facilities, and these together accounted for approximately 70% of the incidents. Facility-wise total number of cases was the highest in lunch facilities followed by restaurants, and these together accounted for 80% of the cases. Fish associated with histamine poisoning were mainly tuna, marlin, and mackerel. Based on the current literature review, 23 genera of histamine-producing bacteria were isolated from fish purchased in Japan. The most frequently reported bacteria were Morganella morganii and Photobacterium damselae. Psychrophilic bacteria such as Morganella psychrotolerans and Photobacterium phosphoreum were also isolated. To prevent histamine poisoning, freezing or fast handling of fish and the products during processing and consuming is important because only refrigeration of fish is enough.

Detection of Escherichia albertii in Retail Oysters

ABSTRACT

Escherichia albertii is an emerging foodborne pathogen. Owing to its distribution in river water, it is important to determine the presence of E. albertii in aquaculture-related foods. In this study, we investigated the distribution of E. albertii in retail oyster samples. A total of 427 raw oyster samples (385 Pacific oysters and 42 Japanese rock oysters) were enriched in modified Escherichia coli broth (mEC) or mEC supplemented with novobiocin (NmEC) at 42°C. The cultures were used for E. albertii-specific nested PCR assay, as well as for E. albertii isolation using deoxycholate hydrogen sulfide lactose agar (DHL), DHL supplemented with rhamnose and xylose, and MacConkey agar supplemented with rhamnose and xylose. The population of E. albertii in nested PCR-positive samples was determined using the most-probable-number (MPN) method. E. albertii isolates were subjected to biochemical and genetic characterization. E. albertii was detected in 5 (1.6%) of 315 Pacific oyster samples (one piece each), 2 (2.9%) of 70 Pacific oyster samples (25 g each), and 2 (4.8%) of 42 Japanese rock oyster samples procured from four geographically distinct regions. A total of 64 E. albertii strains were isolated from eight of the nine nested PCR assay-positive oyster samples, and the MPN value was under the detection limit (<3 MPN/10 g). A specific season or month for detecting E. albertii was not observed in this study, suggesting that the pathogen is present in seawater. All the E. albertii isolates, except one, were positive for the virulence factor eae, indicating that these isolates have the potential to infect humans.

HIGHLIGHTS

Multiplex PCR method for differentiating highly pathogenic Yersinia enterocolitica and low pathogenic Yersinia enterocolitica, and Yersinia pseudotuberculosis

A multiplex PCR method for rapid and sensitive diagnosis, differentiating three pathogenic Yersinia groups such as the highly pathogenic Y. enterocolitica, including serotype O8, low pathogenic Y. enterocolitica, and Y. pseudotuberculosis, was developed. Four primer pairs were chosen to detect the genes fyuA, ail, inv, and virF, responsible for the virulence in pathogenic Yersinia species. Under the multiplex PCR conditions, the unique band patterns for the highly pathogenic Y. enterocolitica, low pathogenic Y. enterocolitica, and Y. pseudotuberculosis were generated from Yersinia strains. The detection limit of this method was 10¹-10³ CFU per reaction tube. This multiplex PCR method could detect highly pathogenic Y. enterocolitica O8 from the wild rodent fecal samples that were culture-positive. Therefore, the new multiplex PCR method developed in this study is a useful tool for rapid and sensitive diagnosis, distinguishing three pathogenic Yersinia groups.

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 β-lactamase genes (bla_CMY-2, bla_CTX-M-15, bla_CTX-M-55, and bla_TEM-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 bla_CMY-2 or bla_TEM-52B. Thus, food workers may acquire TGC-resistant Salmonella after the ingestion of contaminated chicken products and further contaminate food products.

Diversification of Escherichia albertii H-Antigens and Development of H-Genotyping PCR

Escherichia albertii is a recently recognized human enteropathogen that is closely related to Escherichia coli. As E. albertii sometimes causes outbreaks of gastroenteritis, rapid strain typing systems, such as the O- and H-serotyping systems widely used for E. coli, will be useful for outbreak investigation and surveillance. Although an O-genotyping system has recently been developed, the diversity of E. albertii H-antigens (flagellins) encoded by fliC genes remains to be systematically investigated, and no H-serotyping or genotyping system is currently available. Here, we analyzed the fliC genes of 243 genome-sequenced E. albertii strains and identified 73 sequence types, which were grouped into four clearly distinguishable types designated E. albertii H-genotypes 1–4 (EAHg1–EAHg4). Although there was a clear sign of intraspecies transfer of fliC genes in E. albertii, none of the four E. albertii H-genotypes (EAHgs) were closely related to any of the 53 known E. coli H-antigens, indicating the absence or rare occurrence of interspecies transfer of fliC genes between the two species. Although the analysis of more E. albertii strains will be required to confirm the low level of variation in their fliC genes, this finding suggests that E. albertii may exist in limited natural hosts or environments and/or that the flagella of E. albertii may function in a limited stage(s) in their life cycle. Based on the fliC sequences of the four EAHgs, we developed a multiplex PCR-based H-genotyping system for E. albertii (EAH-genotyping PCR), which will be useful for epidemiological studies of E. albertii infections.

[Contamination of Pathogenic Escherichia coli in Retail Fresh Vegetables in the Mekong Delta, Vietnam]

From July 2017 to January 2019, total of 645 retail fresh vegetables collected from 19 retail shops and markets was investigated to know the contamination of enterohemorrhagic Escherichia coli (EHEC) and enterotoxigenic E. coli (ETEC). Of 645 samples, 2 samples (0.3%) were positive for pathogenic E. coli. Of 2 pathogenic E. coli positive samples, 1 was EHEC (stx2 positive) and the other was ETEC (sta positive). Two pathogenic E. coli strains were isolated from crisphead lettuce. EHEC strain was not serotyped by commercial antisera and ETEC was serotyped as O20. EHEC and ETEC strains showed multi-drug resistance against 4 and 7 antibiotics, respectively. These results indicate that retail fresh vegetables seem to be not an important source of human EHEC and ETEC infection in the Mekong Delta, Vietnam.

Presence and quantification of pathogenic Arcobacter and Campylobacter species in retail meats available in Japan

We present estimations for the amounts of Arcobacter (A. butzleri, A. cryaerophilus and A. skirrowii) and Campylobacter (C. jejuni, C. coli and C. fetus) species in retail chicken, pork and beef meat using PCR-MPN. Arcobacter butzleri, A. cryaerophilus and C. jejuni were found in 100, 60 and 55% of chicken samples, respectively. No other Arcobacter or Campylobacter species were found in chicken. The MPNs of A. butzleri, A. cryaerophilus and C. jejuni were greater than 10³ per 100 g in 50, 0 and 5% of samples, respectively. The MPN of A. butzleri was higher than that of C. jejuni in 95% of samples. In pork, A. butzleri and A. cryaerophilus were detected in 10 and 11 (50 and 55%) of 20 samples, respectively. No other Arcobacter or Campylobacter species were found in pork. Only one pork sample had more than 10³ MPN per 100 g of A. cryaerophilus. For beef, only two samples tested positive for A. cryaerophilus, at 4600 and 92 MPN per 100 g. Overall, we found that the presence and MPNs of Arcobacter species are very high in chicken. In contrast, the positive ratios of Arcobacter in pork were high as chicken samples, but MPNs were lower than in chicken.

Evaluating Methods for Detecting Escherichia albertii in Chicken Meat

ABSTRACT

Escherichia albertii is an emerging foodborne pathogen. The source of the E. albertii infection in most foodborne outbreaks is unknown because E. albertii is difficult to isolate from suspected food or water. E. albertii has a broad host range among birds and can be isolated from chicken meat. In this study, PCR assay, enrichment, and isolation conditions for detecting E. albertii in chicken meat were evaluated. The growth of 47 E. albertii strains isolated in Japan between 1994 and 2018 and a type strain was evaluated in modified EC broth (mEC) and mEC supplemented with novobiocin (NmEC) and on media containing carbohydrates. The enzyme used for the nested PCR, the enrichment conditions, the most-probable-number (MPN) method, and agar media were also evaluated with chicken meat. To distinguish E. albertii from presumptive non-E. albertii bacteria, desoxycholate hydrogen sulfide lactose agar (DHL), MacConkey agar (MAC), and these agars supplemented with rhamnose and xylose (RX-DHL and RX-MAC, respectively) were used. All E. albertii strains grew in mEC and NmEC at both 36 and 42°C and did not utilize rhamnose, sucrose, or xylose. Both the first and nested PCRs with TaKaRa Ex Taq, which was 10 to 100 times more active than the other enzymes, produced positive results in enrichment culture of 25 g of chicken meat inoculated with >20 CFU of E. albertii and incubated in mEC and NmEC at 42°C for 22 ± 2 h. Thus, the first PCR was sensitive enough to detect E. albertii in chicken meat. The MPN values in mEC and NmEC were 0.5- and 2.3-fold higher than the original inoculated bacterial levels, respectively. E. albertii in chicken meat was more efficiently isolated with enrichment in NmEC (70.1 to 100%) and plating onto RX-DHL (85.4%) and RX-MAC (100%) compared with enrichment in mEC (53.5 to 83.3%) and plating onto DHL (70.1%) and MAC (92.4%). Thus, optimized conditions for the surveillance of E. albertii contamination in food and investigations of E. albertii outbreaks, including the infectious dose, were clarified.

HIGHLIGHTS

Indoor Fungal Contamination in Temporary Housing after the East Japan Great Earthquake Disaster

To understand fungal contamination in the indoor environment of the disaster region, a field survey was performed to measure the number of fungal counts and identify isolates in the indoor air of prefabricated temporary housing, privately independent-housing, and rented apartments flooded by the East Japan Great Earthquake disaster tsunami. As a result, the period with the highest detected fungal count was from the rainy season to summer in independent-housing and rented apartments. Moreover, in the temporary housing, the fungal number increased further in winter as indicated by the maximum fungal-number throughout the measurement period. The detection frequency of Aspergillus species was relatively higher in the indoor air of temporary housing than in typical housing in the non-disaster area. Since Aspergillus is known as an allergenic genus, it requires careful attention to the health risk for residents. The extremely high level of fungal condensation in indoor air possibly occurred due to high relative humidity and loss of heat insulation in the building attics. It is suggested that this problem commonly happened in the cold region including the entire disaster region of the East Japan Great Earthquake.

Retail fresh vegetables as a potential source of Salmonella infection in the Mekong Delta, Vietnam

From July 2017 to Jan 2019, a total of 572 retail fresh vegetables were collected to clarify the contamination of Salmonella in the Mekong Delta, Vietnam. Salmonella was isolated from 74 (12.9%) of 572 samples. The isolation rate of Salmonella from retail fresh vegetables in the rainy season (15.3%) was significantly higher than that in the dry season (7.6%) (P < 0.05). Of 74 Salmonella isolates, Salmonella Weltevreden was the most predominant serovar (35.1%) identified from retail fresh vegetables in all of the wet markets. All S. Weltevreden isolates (100%) were susceptible to nine antibiotics examined. Thus, retail fresh vegetables were considered as an important potential vehicle of Salmonella transmission to humans in the Mekong Delta. These results provide important data for preventing and controlling human salmonellosis in this area.

[Discovery of Putative Anti-Kudoa septempunctata Chemical Agents by Comprehensive Assay]

We screened 360 chemicals and discovered that 71 chemicals had anti-Kudoa septempunctata effect. Especially 19 and seven of 71 chemicals were antibiotics and antibacterial agents/disinfectants, respectively. The other 45 chemicals were pesticides, natural toxins, industrial chemicals and medicines for non-infectious diseases. Nineteen antibiotics that possessed anti-Kudoa effect contained four tetracyclines, one steroid, two macrolides, one aminoglycoside, three β-lactams, one quinolone, two rifamycines, one polyene, one novobiocine, one sulfonamide and two nitroimidazoles. To use these drugs for prevention of Kudoa infection, the further study is need for the determination of effective dose.

[Assessment of Modified Forms of Fumonisins in Corn-Based Products Retailed in Japan by an Alkaline Hydrolysis Method]

Fumonisins, which are secondary metabolites produced by some Fusarium species, are detected mainly in corn and corn-based products. Recently, the presence of modified forms of fumonisins in fumonisin-contaminated food products has been reported. In order to evaluate the health risk of modified forms of fumonisins to the Japanese population, we analyzed modified forms of fumonisins in corn-based products retailed in Japan. The modified and free forms of fumonisins in food samples were hydrolyzed by alkaline treatment. The resulting hydrolyzed fumonisins were quantified by LC-MS/MS, and total fumonisins (sum of modified and free forms) was calculated. A total of 166 samples of corn-based products were analyzed over two years. The relative ratios of mean total fumonisins to mean free fumonisins in the cornflakes, corn snacks, corn flour and powdered corn soup samples were 4.7, 2.8, 2.1 and 1.2, respectively. Total fumonisins in the residual solid of five cornflake and three corn snack samples obtained after extraction with methanol-water (3 : 1) were quantified. In the cornflakes and corn snacks samples, 56-72 and 83-98% of the modified forms of fumonisins were present in the residual solid, respectively. The average daily intake of fumonisins from cornflakes and corn snacks by the Japanese population was estimated at 1.1 to 3.9 ng/kg body weight/day when the results of free fumonisins were used for the estimate, but when the results of total fumonisins were used, average daily intake increased about three times and was estimated at 3.3 to 12.5 ng/kg body weigh/day. These results indicate that a risk assessment of fumonisins, including the modified forms of fumonisins, is necessary in order to evaluate the true risk of fumonisins to Japanese people.

Discrimination between edible and poisonous mushrooms among Japanese Entoloma sarcopum and related species based on phylogenetic analysis and insertion/deletion patterns of nucleotide sequences of the cytochrome oxidase 1 gene

Entoloma sarcopum is widely known as an edible mushroom but appears morphologically similar to the poisonous mushrooms E. rhodopolium sensu lato (s. l.) and E. sinuatum s. l. Many cases of food poisoning caused by eating these poisonous mushrooms occur each year in Japan. Therefore, they were recently reclassified based on both morphological and molecular characteristics as sensu stricto species. In this study, we analyzed the nucleotide sequences of the rRNA gene (rDNA) cluster region, mainly including the internal transcribed spacer regions and mitochondrial cytochrome oxidase 1 (CO1) gene, in E. sarcopum and its related species, to evaluate performances of these genes as genetic markers for identification and molecular phylogenetic analysis. We found that the CO1 gene contained lineage-specific insertion/deletion sequences, and our CO1 tree yielded phylogenetic information that was not supported by analysis of the rDNA cluster region sequence. Our results suggested that the CO1 gene is a better genetic marker than the rDNA cluster region, which is the most widely used marker for fungal identification and classification, for discrimination between edible and poisonous mushrooms among Japanese E. sarcopum and related species. Our study thus reports a new genetic marker that is useful for detection of Japanese poisonous mushrooms, Entoloma.

An interlaboratory study on the detection methods for enterotoxigenic Escherichia coli in vegetables using enterotoxin gene screening and selective agars for ETEC-specific isolation

Enterotoxigenic Escherichia coli (ETEC) causes acute diarrhea and is transmitted through contaminated food and water; however, systematic procedures for its specific detection in foods have not been established. To establish an efficient detection method for ETEC in food, an interlaboratory study using ETEC O148 and O159 as representative serogroups was first conducted with 13 participating laboratories. A series of tests including enrichment, real-time PCR assays, plating on selective agars, and concentration by immunomagnetic separation followed by plating onto selective agar (IMS-plating methods) were employed. This study particularly focused on the detection efficiencies of real-time PCR assays for enterotoxin genes (sth, stp, and lt), IMS-plating methods, and direct plating onto sorbitol MacConkey agar and CHROMagar STEC medium, supplemented with tobramycin, which is a novel modification in the preparation of a selective agar. Cucumber and leek samples inoculated with ETEC O148 and O159, either at 4-7 CFU/25 g (low levels) or at 21-37 CFU/25 g (high levels) were used as samples with uninoculated samples used as controls. At high inoculation levels, the sensitivities of sth, stp, and lt detection, direct-plating, and IMS-plating methods in cucumber inoculated with O148 and in both foods inoculated with O159 were 100%. In leek inoculated with high levels of O148, the sensitivities of sth, stp, and lt detection, direct-plating, and the IMS-plating method were 76.9%, 64.1%, and 74.4%, respectively. At low inoculation levels, the sensitivities of sth, stp, and lt detection, direct plating, and IMS-plating method in cucumber inoculated with O148 and in both foods inoculated with O159 were in the range of 87.2-97.4%. In leek inoculated with low levels of O148, the sensitivities of sth, stp, and lt detection, direct plating, and the IMS-plating method were 59.0%, 33.3%, and 38.5%, respectively. Thus, ETEC in food contaminated with more than 21 CFU/25 g were detected at high rate (over 74%) using real-time PCR assays and IMS-plating onto selective agar. Therefore, screening sth, stp, and lt genes followed by isolation of STEC using the IMS-plating method may be an efficient method for ETEC detection.

Comprehensive Fungal Community Analysis of House Dust Using Next-Generation Sequencing

Fungal community analyses in homes have been attracting attention because fungi are now generally considered to be allergens. Currently, these analyses are generally conducted using the culture method, although fungal communities in households often contain species that are difficult to culture. In contrast, next-generation sequencing (NGS) represents a comprehensive, labor- and time-saving approach that can facilitate species identification. However, the reliability of the NGS method has not been compared to that of the culture method. In this study, in an attempt to demonstrate the reliability of this application, we used the NGS method to target the internal transcribed spacer 1 (ITS1) in the fungal genome, conducted fungal community analyses for 18 house-dust samples and analyzed fungal community structures. The NGS method positively correlated with the culture method regarding the relative abundance of Aspergillus, Penicillium, Cladosporium and yeasts, which represent the major fungal components found in houses. Furthermore, several genera, such as Malassezia, could be sensitively detected. Our results imply that the reliability of the NGS method is comparable to that of the culture method and indicates that easily available databases may require modifications, including the removal of registrations that have not been sufficiently classified at the genus level.

A New Protocol for the Detection of Sterigmatocystin-producing Aspergillus Section Versicolores Using a High Discrimination Polymerase

Aspergillus section Versicolores species, except Aspergillus sydowii, produce a carcinogenic mycotoxin sterigmatocystin (STC). Since these fungi are found in varied environmental milieu including indoor dust and food products, our aim was to develop a sensitive and convenient assay to detect STC producing fungal strains. We made use of a high discrimination DNA polymerase (HiDi DNA polymerase), for single nucleotide polymorphism (SNP)-based PCR amplification. Using specific primer pairs based on the SNPs between A. sydowii and other strains of Aspergillus section Versicolores, we succeeded in amplifying the genomic DNA all target strains except A. sydowii. These results confirm that the SNP-based PCR amplification technique, using a high discrimination DNA polymerase, was a reliable and robust screening method for target fungal strains.

O-antigen biosynthesis gene clusters of Escherichia albertii: their diversity and similarity to Escherichia coli gene clusters and the development of an O-genotyping method

Escherichia albertii is a recently recognized human enteropathogen that is closely related to Escherichia coli. In many Gram-negative bacteria, including E. coli, O-antigen variation has long been used for the serotyping of strains. In E. albertii, while eight O-serotypes unique to this species have been identified, some strains have been shown to exhibit genetic or serological similarity to known E. coli/Shigella O-serotypes. However, the diversity of O-serotypes and O-antigen biosynthesis gene clusters (O-AGCs) of E. albertii remains to be systematically investigated. Here, we analysed the O-AGCs of 65 E. albertii strains and identified 40 E. albertii O-genotypes (EAOgs) (named EAOg1–EAOg40). Analyses of the 40 EAOgs revealed that as many as 20 EAOgs exhibited significant genetic and serological similarity to the O-AGCs of known E. coli/Shigella O-serotypes, and provided evidence for the inter-species horizontal gene transfer of O-AGCs between E. albertii and E. coli. Based on the sequence variation in the wzx gene among the 40 EAOgs, we developed a multiplex PCR-based O-genotyping system for E. albertii (EAO-genotyping PCR) and verified its usefulness by genotyping 278 E. albertii strains from various sources. Although 225 (80.9 %) of the 278 strains could be genotyped, 51 were not assigned to any of the 40 EAOgs, indicating that further analyses are required to better understand the diversity of O-AGCs in E. albertii and improve the EAO-genotyping PCR method. A phylogenetic view of E. albertii strains sequenced so far is also presented with the distribution of the 40 EAOgs, which provided multiple examples for the intra-species horizontal transfer of O-AGCs in E. albertii.

[DNA Extraction for Sensitive Detection of Shiga Toxin-Producing Escherichia coli in Food by Real-Time PCR Assays]

Alkali-heat DNA extraction, a rapid and economical method, was evaluated for use in the detection of Shiga toxin-producing Escherichia coli in food using real-time PCR assays. Alkali-heat DNA extracts led to highly sensitive detection (10²-10⁴ CFU/mL) of stx and O-antigen genes in beef liver, ground beef, sliced pork, cheese, lettuce, radish sprouts, tomato, and spinach, equivalent to the sensitivity obtained using a commercial DNA extraction kit that utilizes proteinase K lysis, and silica membrane purification. Although there were differences in DNA concentration and purity between DNA extraction methods, the sensitivity of real-time PCR assays was similar. These results indicate that alkali-heat DNA extraction is a viable method when testing food products with real-time PCR assays for the presence of stx and O-antigen genes.

Detection of Kudoa hexapunctata and Kudoa neothunni from retail raw tuna in Japan using a novel duplex polymerase chain reaction

Kudoa hexapunctata was taxonomically separated from Kudoa neothunni, but their main host is tuna. K. hexapunctata has been identified as causative agent of foodborne diseases associated with the ingestion of raw Pacific bluefin tuna (PBT) in Japan, but K. neothunni has not. Therefore, it is clinically and epidemiologically important to detect and distinguish these two species. In the present study, we developed a novel duplex polymerase chain reaction (dPCR) targeting the 28S rRNA gene sequences of K. hexapunctata and K. neothunni. The dPCR amplified the desired genetic regions of each species, and the detection limit was 10 copies/reaction. A total of 36 retail tuna samples from different fishing ports were purchased and tested by dPCR. Thirty-one tested positive for K. hexapunctata and four tested positive for K. neothunni. Several retail PBT samples were examined in some of the fishing ports, and among these samples, the detection rates of K. hexapunctata was higher than 85%, and the rates were similar between wild and farmed PBT. The detection rates of K. hexapunctata in wild and farmed retail PBT were 75% and 71%, respectively, in May. However, the rates in June and July were 100% for both. K. hexapunctata and K. neothunni myxospores were not observed in the dPCR-positive samples, except in juvenile PBT, suggesting that the number of parasites was insufficient to cause foodborne disease. Thus, dPCR is a useful method for detecting and distinguishing K. hexapunctata and K. neothunni, and can be used in epidemiological studies of these parasites.

Development of Amphipathic Antimicrobial Peptide Foldamers Based on Magainin 2 Sequence

Magainin 2 (Mag 2), which is isolated from the skin of frogs, is a representative antimicrobial peptide (AMP), exerts its antimicrobial activity via microbial membrane disruption. It has been reported that both the amphipathicity and helical structure of Mag 2 play an important role in its antimicrobial activity. In this study, we revealed that the sequence of 17 amino acid residues in Mag 2 (peptide 7) is required to exert sufficient activity. We also designed a set of Mag 2 derivatives, based on enhancement of helicity and/or amphipathicity, by incorporation of α,α-disubstituted amino acid residues into the Mag 2 fragment, and evaluated their preferred secondary structures and their antimicrobial activities against both Gram-positive and Gram-negative bacteria. As a result, peptide 11 formed a stable helical structure in solution, and possessed potent antimicrobial activities against both Gram-positive and Gram-negative bacteria without significant cytotoxicity.

Determination of sterigmatocystin in foods in Japan: method validation and occurrence data

A survey of the contamination of foods by sterigmatocystin (STC) was performed by an analytical method based on LC-MS/MS. STC was extracted from samples with acetonitrile/water (85/15, v/v) and then purified with immunoaffinity columns. The method was validated by a small-scale inter-laboratory study using spiked wheat samples. Mean recoveries of STC were 100.3% and 92.5% from two samples spiked at 0.5 and 5.0 µg/kg, respectively. A total of 583 samples were analysed between 2016 and 2018, and STC was detected in 19.9% of all samples at >0.05 μg/kg (limit of quantification). The foods that were contaminated by STC were wheat flour, Job's tears products, rye flour, rice, buckwheat flour, white sorghum, barley products, azuki bean and corn flour. STC was not found in beer or wine. The occurrence of STC in domestic wheat flour (44.4%), Job's tears products (41.7%) and rye flour (29.9%) accounted for the three highest values. The highest mean concentrations were obtained for Job's tears products (0.3 μg/kg) and rye flour (0.3 μg/kg). The maximum contamination level was present in a sample of rye flour (7.1 μg/kg). Although the contamination levels were low, these results indicate that STC frequently contaminates Japanese retail foods. A continuous survey is required to assess exposure to STC in Japan.

Prevalence of Diarrheagenic Escherichia coli in Foods and Fecal Specimens Obtained from Cattle, Pigs, Chickens, Asymptomatic Carriers, and Patients in Osaka and Hyogo, Japan

The source and routes of diarrheagenic Escherichia coli (DEC) remain poorly understood. To investigate the involvement of domestic animals in the dissemination of DEC, the prevalence of DEC in foods and fecal specimens from cattle, pigs, chickens, healthy carriers, and patients in Osaka and Hyogo, Japan was investigated using a multiplex real-time Polymerase Chain Reaction assay. The most abundant virulence genes were astA and eae, which had a prevalence 46.8% and 27.4%, respectively. Additionally, stx1 (26.6%) and stx2 (45.9%) were prevalent in cattle feces, while est (8.5%) and elt (7.6%) were prevalent in pig feces. afaB was the second-most prevalent gene in patients and healthy carriers, and it had detection rates of 5.1% and 8.1%, respectively. In contrast, afaB was not detected in animal feces or foods, except for three porcine fecal samples. The aggR gene was more prevalent in humans than in foods or animal feces. Both Shiga toxin-producing E. coli and atypical enteropathogenic E. coli carried by cattle may be sources for diarrheal diseases in humans. Pigs may be a source for human enterotoxigenic E. coli infections, whereas humans are expected to be the reservoir for diffusely adhering E. coli, enteroaggregative E. coli, and enteroinvasive E. coli.

Prevalence, antimicrobial resistance and multiple-locus variable-number tandem-repeat analysis profiles of diarrheagenic Escherichia coli isolated from different retail foods

Diarrheagenic E. coli (DEC) isolates were recovered from local retail markets and the Osaka Municipal Central Wholesale Market in Japan. Retail food samples were collected for analysis in Osaka Japan from 2005 to 2008 and consisted of 32 beef, 28 pork, 20 poultry, 136 fish, 66 fruits and vegetables and 51 ready-to-eat (RTE) food samples. A total of 82 DEC strains were recovered from 64 (19%) food samples with the highest prevalence in poultry (100%, 20/20), followed by pork (54%, 15/28), beef (28%, 9/32), fruits and vegetables (12%, 8/66), fish (6.6%, 9/136) and RTE foods (5.9%, 3/51). Most of the strains belonged to E. coli possessing the enteroaggregative E. coli (EAEC) heat-stable enterotoxin 1 (EAST1) gene (EAST1EC; n=62, P<0.0001) and enteropathogenic E. coli (EPEC; n=16, P<0.01), whereas only 1 strain belonged to Shiga toxin-producing E. coli (STEC), 1 to EAEC and 2 to enterotoxigenic E. coli (ETEC) strains. Of the 82 DEC isolates, 22 O and 13H serogroups were detected, including some specific serogroups (O91, O103, O115, O119, O126, and O157) which have been associated with human diarrheal infections. Phylogenetic group A and B1 were predominant among the DEC isolates. Antimicrobial resistance to tetracycline was most common (49%), followed by nalidixic acid (28%), ampicillin (24%), sulfamethoxazole/trimethoprim (20%), and cephalothin (18%). All isolates were susceptible to aztreonam. Of the resistant strains, 44% (22/50) demonstrated resistance to >3 antimicrobial agents. Isolates resistant to >5 antimicrobials were only found in the meat samples, while isolates from the fruits and vegetables as well as RTE foods showed resistance to only 1 or 2 antimicrobial agents. Sixty one percent of EAST1EC, 56% of EPEC and all of the EAEC and ETEC were resistant to at least 1 antimicrobial agent. Multiple-locus variable-number tandem repeat analysis (MLVA) was used in this study for genotyping of DEC. The 82 isolates collected for this study showed 77 distinct MLVA profiles located among 3 branches. The Simpson's Index of Diversity (D) was 99.9% at its highest. The high diversity of these food strains would suggest their originating from a variety of sources and environments. In conclusion, retail food samples in Japan were contaminated with DEC; EAST1EC, a putative DEC, were detected at high rates in poultry, pork and beef. Isolates resistant to >3 antimicrobials were found only in raw meat and fish. Food animals may act as the reservoir for multi-resistant bacteria. Due to the finding that nearly 1/3 of EAST1EC strains were resistant to >3 antimicrobials, additional surveillance for EAST1EC should be initiated.

Comparison by multilocus variable-number tandem repeat analysis and antimicrobial resistance among atypical enteropathogenic Escherichia coli strains isolated from food samples and human and animal faecal specimens

AIM

This study assessed whether multilocus variable-number tandem repeat analysis (MLVA) and antimicrobial susceptibility testing discriminated diarrhoeagenic atypical enteropathogenic Escherichia coli (aEPEC) from aEPEC indigenous to domestic animals or healthy people.

METHODS AND RESULTS

MLVA genotyping of 142 aEPEC strains isolated from foods and faecal samples of domestic animals and humans revealed 126 distinct MLVA profiles that distributed to four clusters, yielding a Simpson's index of diversity (D) of 99·8%. Cluster 2 included 87% of cattle isolates and 67% of patient isolates. The plurality (15/34, 44%) of strains from healthy humans mapped to Cluster 1, while half (18/41, 44%) of the swine strains belonged to Cluster 4. Testing for antimicrobial susceptibility revealed that 52 strains (37%) of aEPEC were resistant to one or more agents; only 10 strains (7%) exhibited resistance to more than three agents. Strains isolated from swine or food exhibited a wider variety of resistance phenotypes than bovine or human strains.

CONCLUSIONS

MLVA assigned the aEPEC isolates from cattle and patients to Cluster 2, distinct from aEPEC from other sources. Hog yards may be a larger source of drug-resistant strains than are cattle ranches.

SIGNIFICANCE AND IMPACT OF THE STUDY

MLVA suggests that human diarrhoeagenic aEPEC are derived from cattle and are distinct from strains carried by healthy people and other animals. Cattle appear to be reservoirs of human diarrhoeagenic aEPEC.

Characterization of unstable pEntYN10 from enterotoxigenic Escherichia coli (ETEC) O169:H41

Enterotoxigenic Escherichia coli (ETEC) serotype O169:H41 has been an extremely destructive epidemic ETEC type worldwide. The strain harbors a large unstable plasmid that is regarded as responsible for its virulence, although its etiology has remained unknown. To examine its genetic background specifically on the unstable retention and responsibility in the unique adherence to epithelial cells and enterotoxin production, the complete sequence of a plasmid, pEntYN10, purified from the serotype strain was determined. The length is 145,082 bp; its GC content is 46.15%. It contains 182 CDSs, which include 3 colonization factors (CFs), an enterotoxin, and large number of insertion sequences. The repertory of plasmid stability genes was extraordinarily scant. Uniquely, results showed that 3 CFs, CS6, CS8 (CFA/III)-like, and K88 (F4)-like were encoded redundantly in the plasmid with unique variations among previously known subtypes. These three CFs preserved their respective gene structures similarly to those of other ETEC strains reported previously with unique sequence variations respectively. It is particularly interesting that the K88-like gene cluster of pEntYN10 had 2 paralogous copies of faeG, which encodes the major component of fimbrial structure. It remains to be verified how the unique variations found in the CFs respectively affect the affinity to infected cells, host range, and virulence of the ETEC strain.

An interlaboratory study on efficient detection of Shiga toxin-producing Escherichia coli O26, O103, O111, O121, O145, and O157 in food using real-time PCR assay and chromogenic agar

To establish an efficient detection method for Shiga toxin (Stx)-producing Escherichia coli (STEC) O26, O103, O111, O121, O145, and O157 in food, an interlaboratory study using all the serogroups of detection targets was firstly conducted. We employed a series of tests including enrichment, real-time PCR assays, and concentration by immunomagnetic separation, followed by plating onto selective agar media (IMS-plating methods). This study was particularly focused on the efficiencies of real-time PCR assays in detecting stx and O-antigen genes of the six serogroups and of IMS-plating methods onto selective agar media including chromogenic agar. Ground beef and radish sprouts samples were inoculated with the six STEC serogroups either at 4-6CFU/25g (low levels) or at 22-29CFU/25g (high levels). The sensitivity of stx detection in ground beef at both levels of inoculation with all six STEC serogroups was 100%. The sensitivity of stx detection was also 100% in radish sprouts at high levels of inoculation with all six STEC serogroups, and 66.7%-91.7% at low levels of inoculation. The sensitivity of detection of O-antigen genes was 100% in both ground beef and radish sprouts at high inoculation levels, while at low inoculation levels, it was 95.8%-100% in ground beef and 66.7%-91.7% in radish sprouts. The sensitivity of detection with IMS-plating was either the same or lower than those of the real-time PCR assays targeting stx and O-antigen genes. The relationship between the results of IMS-plating methods and Ct values of real-time PCR assays were firstly analyzed in detail. Ct values in most samples that tested negative in the IMS-plating method were higher than the maximum Ct values in samples that tested positive in the IMS-plating method. This study indicates that all six STEC serogroups in food contaminated with more than 29CFU/25g were detected by real-time PCR assays targeting stx and O-antigen genes and IMS-plating onto selective agar media. Therefore, screening of stx and O-antigen genes followed by isolation of STECs by IMS-plating methods may be an efficient method to detect the six STEC serogroups.

Association of Cell-adhesion Activities with Virulence in Shiga toxin-producing Escherichia coli O103：H2

The characteristics of 11 strains of Stx1-producing and Stx2-non-producing STEC O103：H2 were analyzed to investigate the differences in virulence in a single serotype of Shiga toxin (Stx) -producing Escherichia coli (STEC). Differences in the cell-adhesion activity to Caco-2 cells were observed among the strains. The activity of the one strain, isolated from a patient with hemolytic uremic syndrome was 4-20-fold higher than those of the other strains. Although the strains with high cell-adhesion activity showed high expressions of eae, espB, espD, and tir in the locus of enterocyte effacement related with cell-adhesion, those were not specific for this strain. In addition, the Stx1 production level of the strain was not particularly high. It was indicated that the high adhesion activity might be a potential factor to associate serious symptom.

[Molecular Detection Methods for Vibrio parahaemolyticus in Seafood]

To detect Vibrio parahaemolyticus in seafood, we evaluated efficient combinations of molecular methods with DNA extraction methods using heat extraction and alkaline heat extraction, and PCR, real-time PCR and loop-mediated isothermal amplification (LAMP) assays were performed targeting V parahaemolyticus species-specific genes (tlh and rpoD) and pathogenic factors genes (tdh and trh). The species-specific genes were detected in all combinations of two strains (a tdh * trh1-positive strain and a trh2-positive strain), two kinds of shellfish (oyster and bloody clams) and molecular methods with tlh-real time PCR or rpoD-LAMP assays with DNA of alkaline heat extraction at 85-145cfu/test level. tdh was detected in both seafoods with real time PCR assay with DNA of heat extraction at 85cfu/test level, and detected with the LAMP and real time PCR assays with DNA of alkaline heat extraction at 85cfu/test level. Detection of both trh1 and trh2 with the PCR assay with DNA of alkaline heat extraction was comparatively high though trh2 was detected with the LAMP assay with DNA of alkaline heat extraction at 145cfu/test level. It, however, is necessary to investigate more sensitive trh-detection methods. In this study, the results indicated that tlh-real time PCR or rpoD-LAMP, tdh-real time PCR and tdh-LAMP assays with DNA of alkaline heat extraction are relatively-sensitive methods to detect V. parahaemolyticus in seafood.

Phylogenetic Clades 6 and 8 of Enterohemorrhagic Escherichia coli O157:H7 With Particular stx Subtypes are More Frequently Found in Isolates From Hemolytic Uremic Syndrome Patients Than From Asymptomatic Carriers

EHEC O157:H7 clade 6 strains harboring stx2a and/or stx2c and clade 8 strains harboring stx2a or stx2a/stx2c were frequently associated with childhood HUS cases in Japan. Rapid and specific detection of such lineages are required for infection control measures.

Background

 Enterohemorrhagic Escherichia coli (EHEC) O157:H7 infection causes severe diseases such as bloody diarrhea and hemolytic uremic syndrome (HUS). Although EHEC O157:H7 strains have exhibited high genetic variability, their abilities to cause human diseases have not been fully examined.

Methods

 Clade typing and stx subtyping of EHEC O157:H7 strains, which were isolated in Japan during 1999–2011 from 269 HUS patients and 387 asymptomatic carriers (ACs) and showed distinct pulsed-field gel electrophoresis patterns, were performed to determine relationships between specific lineages and clinical presentation.

Results

 Clades 6 and 8 strains were more frequently found among the isolates from HUS cases than those from ACs (P = .00062 for clade 6, P < .0001 for clade 8). All clade 6 strains isolated from HUS patients harbored stx2a and/or stx2c, whereas all clade 8 strains harbored either stx2a or stx2a/stx2c. However, clade 7 strains were predominantly found among the AC isolates but less frequently found among the HUS isolates, suggesting a significant association between clade 7 and AC (P < .0001). Logistic regression analysis revealed that 0–9 year old age is a significant predictor of the association between clade 8 and HUS. We also found an intact norV gene, which encodes for a nitric oxide reductase that inhibits Shiga toxin activity under anaerobic condition, in all clades 1–3 isolates but not in clades 4–8 isolates.

Conclusions

 Early detection of EHEC O157:H7 strains that belonged to clades 6/8 and harbored specific stx subtypes may be important for defining the risk of disease progression in EHEC-infected 0- to 9-year-old children.

[Histamine formation in Japanese marine fish species and the effect of frozen storage]

To investigate histamine formation in Japanese marine fish, model samples were made from fish meat mixed with intestines of commercial 73 fish species. After the samples were stored at 25℃ for 12 hr, histamine was detected in 35 fish species at 50 mg/kg or more. These fish species might potentially be related to histamine poisoning. In addition, the effect of frozen storage at -45℃ on histamine formation was examined. Although histamine was formed in some fish species, and Photobacterium damselae and Photobacterium iliopiscarium were isolated from the frozen samples, the amount of histamine formed in the model samples was reduced in all tested fish species after frozen storage. Therefore frozen storage of fish may be effective to control histamine formation, even though histamine forming bacteria survived under these conditions.

Characteristics of bacterial and fungal growth in plastic bottled beverages under a consuming condition model

Microbial contamination in unfinished beverages can occur when drinking directly from the bottle. Various microorganisms, including foodborne pathogens, are able to grow in these beverages at room temperature or in a refrigerator. In this study, we elucidated the characteristics of microorganism growth in bottled beverages under consuming condition models. Furthermore, we provide insight into the safety of partially consumed bottled beverages with respect to food hygiene. We inoculated microorganisms, including foodborne pathogens, into various plastic bottled beverages and analysed the dynamic growth of microorganisms as well as bacterial toxin production in the beverages. Eight bottled beverage types were tested in this study, namely green tea, apple juice drink, tomato juice, carbonated drink, sport drink, coffee with milk, isotonic water and mineral water, and in these beverages several microorganism types were used: nine bacteria including three toxin producers, three yeasts, and five moulds. Following inoculation, the bottles were incubated at 35°C for 48 h for bacteria, 25°C for 48 h for yeasts, and 25°C for 28 days for moulds. During the incubation period, the number of bacteria and yeasts and visible changes in mould-growth were determined over time. Our results indicated that combinations of the beverage types and microorganism species correlated with the degree of growth. Regarding factors that affect the growth and toxin-productivity of microorganisms in beverages, it is speculated that the pH, static/shaking culture, temperature, additives, or ingredients, such as carbon dioxide or organic matter (especially of plant origin), may be important for microorganism growth in beverages. Our results suggest that various types of unfinished beverages have microorganism growth and can include food borne pathogens and bacterial toxins. Therefore, our results indicate that in terms of food hygiene it is necessary to consume beverages immediately after opening the bottle.

Spread and change in stress resistance of Shiga toxin-producing Escherichia coli O157 on fungal colonies

To elucidate the effect of fungal hyphae on the behaviour of Shiga toxin-producing Escherichia coli (STEC) O157, the spread and change in stress resistance of the bacterium were evaluated after coculture with 11 species of food-related fungi including fermentation starters. Spread distances of STEC O157 varied depending on the co-cultured fungal species, and the motile bacterial strain spread for longer distances than the non-motile strain. The population of STEC O157 increased when co-cultured on colonies of nine fungal species but decreased on colonies of Emericella nidulans and Aspergillus ochraceus. Confocal scanning microscopy visualization of green fluorescent protein-tagged STEC O157 on fungal hyphae revealed that the bacterium colonized in the water film that existed on and between hyphae. To investigate the physiological changes in STEC O157 caused by co-culturing with fungi, the bacterium was harvested after 7 days of co-culturing and tested for acid resistance. After co-culture with eight fungal species, STEC O157 showed greater acid resistance compared to those cultured without fungi. Our results indicate that fungal hyphae can spread the contamination of STEC O157 and can also enhance the stress resistance of the bacteria.