[Major Vehicles and O-Serogroups in Foodborne Enterotoxigenic Escherichia coli Outbreaks in Japan, and Effective Detection Methods of the Pathogen in Food Associated with An Outbreak].

Enterotoxigenic Escherichia coli (ETEC) is a common pathogen in developing countries, and causes foodborne infections through contaminated vegetables and water. ETEC also caused some foodborne infections in developed countries, though the vehicles are often unclear. We analyzed ETEC foodborne outbreaks in Japan based on the National Food Poisoning Statistics. Vegetables and private well water accounted for 50% and 22.2% of vehicles, respectively. The main vehicles were similar to those in developing countries. Serogroups of ETEC were also analyzed, and O6, O25, O27, O148, O153, O159, and O169 were the seven major O-serogroups. We investigated suitable detection methods for the pathogen (O148) in food samples associated with an outbreak of ETEC in Japan in 2011. We show that ETEC O148 could be effectively detected in cut leeks by means of a two-step enrichment and real-time PCR assay targeting heat-stable enterotoxin gene. Our survey of the vehicles and the major O-serogroups of ETEC outbreaks in Japan indicates that ETEC survives in the environment in Japan.

Characterization of enterohemorrhagic Escherichia coli O111 and O157 strains isolated from outbreak patients in Japan.

In April and May 2011, there was a serious food-poisoning outbreak in Japan caused by enterohemorrhagic Escherichia coli (EHEC) strains O111:H8 and O157:H7 from raw beef dishes at branches of a barbecue restaurant. This outbreak involved 181 infected patients, including 34 hemolytic-uremic syndrome (HUS) cases (19%). Among the 34 HUS patients, 21 developed acute encephalopathy (AE) and 5 died. Patient stool specimens yielded E. coli O111 and O157 strains. We also detected both EHEC O111 stx2 and stx-negative E. coli O111 strains in a stock of meat block from the restaurant. Pulsed-field gel electrophoresis (PFGE) and multilocus variable-number tandem-repeat analysis (MLVA) showed that the stx-negative E. coli O111 isolates were closely related to EHEC O111 stx2 isolates. Although the EHEC O157 strains had diverse stx gene profiles (stx1, stx2, and stx1 stx2), the PFGE and MLVA analyses indicated that these isolates originated from a single clone. Deletion of the Stx2-converting prophage from the EHEC O111 stx2 isolates was frequently observed during in vitro growth, suggesting that strain conversion from an EHEC O111 stx2 to an stx-negative strain may have occurred during infection.

Inference of the impact of insertion sequence (IS) elements on bacterial genome diversification through analysis of small-size structural polymorphisms in Escherichia coli O157 genomes.

Mobile genetic elements play important roles in the evolution and diversification of bacterial genomes. In enterohemorrhagic Escherichia coli O157, a major factor that affects genomic diversity is prophages, which generate most of the large-size structural polymorphisms (LSSPs) observed in O157 genomes. Here, we describe the results of a systematic analysis of numerous small-size structural polymorphisms (SSSPs) that were detected by comparing the genomes of eight clinical isolates with a sequenced strain, O157 Sakai. Most of the SSSPs were generated by genetic events associated with only two insertion sequence (IS) elements, IS629 and ISEc8, and a number of genes that were inactivated or deleted by these events were identified. Simple excisions of IS629 and small deletions (footprints) formed by the excision of IS629, both of which are rarely described in bacteria, were also detected. In addition, the distribution of IS elements was highly biased toward prophages, prophage-like integrative elements, and plasmids. Based on these and our previous results, we conclude that, in addition to prophages, these two IS elements are major contributors to the genomic diversification of O157 strains and that LSSPs have been generated mainly by bacteriophages and SSSPs by IS elements. We also suggest that IS elements possibly play a role in the inactivation and immobilization of incoming phages and plasmids. Taken together, our results reveal the true impact of IS elements on the diversification of bacterial genomes and highlight their novel role in genome evolution.

Coordinate control of the locus of enterocyte effacement and enterohemolysin genes by multiple common virulence regulators in enterohemorrhagic Escherichia coli.

The locus of enterocyte effacement (LEE) pathogenicity island is required for the intimate adhesion of enterohemorrhagic Escherichia coli (EHEC) to the intestinal epithelial cells. GrlR and GrlA are LEE-encoded negative and positive regulators, respectively. The interaction of these two regulators is important for controlling the transcription of LEE genes through Ler, a LEE-encoded central activator for the LEE. The GrlR-GrlA regulatory system controls not only LEE but also the expression of the flagellar and enterohemolysin (Ehx) genes in EHEC. Since Ehx levels were markedly induced in a grlR mutant but not in a grlR grlA double mutant and significantly increased by overexpression of GrlA in a ler mutant, GrlA is responsible for this regulation (T. Saitoh et al., J. Bacteriol. 190:4822-4830, 2008). In this study, additional investigations of the regulation of ehx gene expression determined that Ler also acts as an activator for Ehx expression without requiring GrlA function. We recently reported that the LysR-type regulator LrhA positively controls LEE expression (N. Honda et al., Mol. Microbiol. 74:1393-1411, 2009). The hemolytic activity of the lrhA mutant strain of EHEC was lower than that of the wild-type strain, and LrhA markedly induced ehx transcription in an E. coli K-12 strain, suggesting that LrhA also activates the transcription of ehx without GrlA and Ler. Gel mobility shift assays demonstrated that Ler and LrhA directly bind to the regulatory region of ehxC. Together, these results indicate that transcription of ehx is positively regulated by Ler, GrlA, and LrhA, which all act as positive regulators for LEE expression.

LrhA positively controls the expression of the locus of enterocyte effacement genes in enterohemorrhagic Escherichia coli by differential regulation of their master regulators PchA and PchB.

Summary Genes essential for eliciting pathogenicity of enterohemorrhagic Escherichia coli are located within the locus of enterocyte effacement (LEE). Expression of LEE genes is positively regulated by paralogues PchA, PchB and PchC, which are encoded by separate loci of the chromosome. To elucidate the underlying regulatory mechanism, we screened transposon mutants exhibiting reduced expression of pchA, transcription level of which is highest among the pch genes. Here, we report that the LysR-homologue A (LrhA) positively regulated the transcription of pchA and pchB. A deletion in lrhA reduced the transcription levels of pchA and pchB to different degrees, and also reduced the expression of LEE-coded type 3-secreted protein, EspB. Expression of LrhA from a plasmid restored and markedly increased the transcription levels of pchA and pchB respectively, and highly induced EspB expression. Deletion analysis of the regulatory region showed that both promoter-proximal (-195 to +88) and promoter-distal (-418 to -392 for pchA and -391 to -375 for pchB) sequences were required for the LrhA-mediated upregulation of pchA and pchB genes. Purified His(6)-LrhA protein differentially bound to the regulatory regions of pchA/B, suggesting that direct regulation of pchA and pchB genes by LrhA in turn controls the expression of LEE genes.

Plasmid-mediated resistance to cephalosporins in Salmonella enterica serovar Typhi.

This study characterized a cephalosporin-resistant Salmonella enterica serovar Typhi isolate. The organism possessed a plasmid encoding the CTX-M-15 extended-spectrum-beta-lactamase. This plasmid is the determinant for the phenotype of cephalosporin resistance and is transferrable among Enterobacteriaceae.

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.

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.

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.

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.

Development of a multiplex PCR-based rapid typing method for enterohemorrhagic Escherichia coli O157 strains.

Enterohemorrhagic Escherichia coli O157 (EHEC O157) is a food-borne pathogen that has raised worldwide public health concern. The development of simple and rapid strain-typing methods is crucial for the rapid detection and surveillance of EHEC O157 outbreaks. In the present study, we developed a multiplex PCR-based strain-typing method for EHEC O157, which is based on the variability in genomic location of IS629 among EHEC O157 strains. This method is very simple, in that the procedures are completed within 2 h, the analysis can be performed without the need for special equipment or techniques (requiring only conventional PCR and agarose gel electrophoresis systems), the results can easily be transformed into digital data, and the genes for the major virulence markers of EHEC O157 (the stx(1), stx(2), and eae genes) can be detected simultaneously. Using this method, 201 EHEC O157 strains showing different XbaI digestion patterns in pulsed-field gel electrophoresis (PFGE) analysis were classified into 127 types, and outbreak-related strains showed identical or highly similar banding patterns. Although this method is less discriminatory than PFGE, it may be useful as a primary screening tool for EHEC O157 outbreaks.

Utility of multilocus variable-number tandem-repeat analysis as a molecular tool for phylogenetic analysis of Shigella sonnei.

A panel of 916 isolates, including 703 closely related IST1 isolates, were characterized by inter-IS1 spacer typing (IST), pulsed-field gel electrophoresis (PFGE), and multilocus variable-number tandem-repeat (VNTR) analysis (MLVA) to evaluate the utility of MLVA as a molecular tool for the phylogenetic analysis of Shigella sonnei. The global phylogenetic patterns determined by IST, PFGE, and MLVA were concordant. MLVA was carried out using 26 VNTR loci with a range of degrees of variability. MLVA data for the 703 IST1 isolates revealed that diversification among the closely related isolates was attributed mainly to four highly variable loci. The phylogenetic pattern for the closely related isolates determined using MLVA profiles of 8 highly variable loci was in agreement with that determined using the 26-locus profiles. A clustering analysis using the profiles of 18 loci with limited variability established clear phylogenetic relationships among IST clonal groups. Accordingly, MLVA is a useful tool for the phylogenetic analysis of S. sonnei. Combined VNTR loci with higher variability are useful markers for resolving closely related isolates, whereas combined loci with lower variability are suitable for establishing clear phylogenetic relationships between strains or clones that have evolved over a longer timescale.

Multilocus variable-number tandem repeat analysis for molecular typing and phylogenetic analysis of Shigella flexneri.

BACKGROUND: Shigella flexneri is one of the causative agents of shigellosis, a major cause of childhood mortality in developing countries. Multilocus variable-number tandem repeat (VNTR) analysis (MLVA) is a prominent subtyping method to resolve closely related bacterial isolates for investigation of disease outbreaks and provide information for establishing phylogenetic patterns among isolates. The present study aimed to develop an MLVA method for S. flexneri and the VNTR loci identified were tested on 242 S. flexneri isolates to evaluate their variability in various serotypes. The isolates were also analyzed by pulsed-field gel electrophoresis (PFGE) to compare the discriminatory power and to evaluate the usefulness of MLVA as a tool for phylogenetic analysis of S. flexneri. RESULTS: Thirty-six VNTR loci were identified by exploring the repeat sequence loci in genomic sequences of Shigella species and by testing the loci on nine isolates of different subserotypes. The VNTR loci in different serotype groups differed greatly in their variability. The discriminatory power of an MLVA assay based on four most variable VNTR loci was higher, though not significantly, than PFGE for the total isolates, a panel of 2a isolates, which were relatively diverse, and a panel of 4a/Y isolates, which were closely-related. Phylogenetic groupings based on PFGE patterns and MLVA profiles were considerably concordant. The genetic relationships among the isolates were correlated with serotypes. The phylogenetic trees constructed using PFGE patterns and MLVA profiles presented two distinct clusters for the isolates of serotype 3 and one distinct cluster for each of the serotype groups, 1a/1b/NT, 2a/2b/X/NT, 4a/Y, and 6. Isolates that had different serotypes but had closer genetic relatedness than those with the same serotype were observed between serotype Y and subserotype 4a, serotype X and subserotype 2b, subserotype 1a and 1b, and subserotype 3a and 3b. CONCLUSIONS: The 36 VNTR loci identified exhibited considerably different degrees of variability among S. flexneri serotype groups. VNTR locus could be highly variable in a serotype but invariable in others. MLVA assay based on four highly variable loci could display a comparable resolving power to PFGE in discriminating isolates. MLVA is also a prominent molecular tool for phylogenetic analysis of S. flexneri; the resulting data are beneficial to establish clear clonal patterns among different serotype groups and to discern clonal groups among isolates within the same serotype. As highly variable VNTR loci could be serotype-specific, a common MLVA protocol that consists of only a small set of loci, for example four to eight loci, and that provides high resolving power to all S. flexneri serotypes may not be obtainable.

Interaction between enterohemorrhagic Escherichia coli O157:H7 EspFu and IRSp53 induces dynamic membrane remodeling in epithelial cells.

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 induces the formation of filamentous, actin-rich, pedestal-shaped structures beneath bacterial cells that have attached to intestinal epithelial cells. Pedestal formation requires the translocation of EHEC O157:H7 type III effectors. One of these type III effectors, EspFu, consists of an N-terminal signal sequence, which is necessary for the translocation of EspFu into the host cell through a type III secretion system, and almost identical proline-rich repeats (PRRs), which control actin rearrangement and increase the efficiency of actin assembly in the host cell. In this study, we report that insulin receptor tyrosine kinase substrate p53 (IRSp53) in the host cell acts as a binding partner for EspFu. Co-immunoprecipitation and fluorescence microscopy showed specific interactions between EspFu and IRSp53 as well as their co-localization in epithelial cells. Additionally, we demonstrated that the association between EspFu and IRSp53 induces dynamic membrane remodeling in epithelial cells.

Yersinia infection in two captive guereza colobus monkeys (Colobus guereza).

Two guereza colobus monkeys (Colobus guereza) reared in a zoological garden in Japan suddenly died of multifocal fibrinonecrotic gastroenteritis and septicemia associated with infection by Yersinia spp. It was necessary to microbiologically differentiate Yersinia frederiksenii and Y. enterocolitica. We described the pathological findings and discuss the causal agent to emphasize the need to revert to using a combination of multiple examinations for diagnosis.

Transcription of the ehx enterohemolysin gene is positively regulated by GrlA, a global regulator encoded within the locus of enterocyte effacement in enterohemorrhagic Escherichia coli.

The pathogenicity island termed locus of enterocyte effacement (LEE) encodes a type 3 protein secretion system, whose function is required for full virulence of enterohemorrhagic Escherichia coli (EHEC). GrlR and GrlA are LEE-encoded negative and positive regulators, respectively, for controlling transcription of the ler gene, which encodes a central activator of LEE gene expression. We previously reported that the GrlR-GrlA regulatory system controls not only the LEE genes but also flagellar gene expression in EHEC (S. Iyoda et al., J. Bacteriol. 188:5682-5692, 2006). In order to further explore virulence-related genes under the control of the GrlR-GrlA regulatory system, we characterized a grlR-deleted EHEC O157 strain, which was found to have high and low levels of expression of LEE and flagellar genes, respectively. We report here that the grlR deletion significantly induced enterohemolysin (Ehx) activity of EHEC O157 on plates containing defibrinated sheep erythrocytes. Ehx levels were not induced in the grlR grlA double mutant strain but increased markedly by overexpression of GrlA even in the ler mutant, indicating that GrlA is responsible for this regulation. Ehx of the EHEC O157 Sakai strain is encoded by the ehxCABD genes, which are carried on the large plasmid pO157. The expression of ehxC fused with FLAG tag or a promoterless lacZ gene on pO157 was significantly induced under conditions in which GrlA was overproduced. These results together suggest that GrlA acts as a positive regulator for the ehx transcription in EHEC.

Molecular characterization of enterohemorrhagic Escherichia coli O157:H7 isolates dispersed across Japan by pulsed-field gel electrophoresis and multiple-locus variable-number tandem repeat analysis.

We identified seven distinct subtypes of enterohemorrhagic Escherichia coli (EHEC) O157:H7 isolates that were derived from sporadic cases and outbreaks from multiple prefectures in Japan in 2005. A surveillance system utilizing pulsed-field gel electrophoresis (PFGE), PulseNet Japan, was used. Some strains showed indistinguishable PFGE patterns using another restriction enzyme (BlnI or SpeI) in each subtype of EHEC O157:H7 isolates that were routinely subtyped by the XbaI PFGE pattern. In order to examine the genotypic relatedness of these strains, we carried out a multiple-locus variable-number tandem repeat (VNTR) analysis (MLVA). By using the MLVA system, we found that three of seven subtypes of EHEC O157:H7 strains that were isolated from sporadic cases dispersed across multiple prefectures within a few months showed indistinguishable PFGE patterns and identical MLVA types. Strains belonging to the other four subtypes of EHEC O157:H7 in the PFGE analysis were further classified into different clusters of EHEC O157:H7. Therefore, compared to PFGE, MLVA showed greater discriminatory power with respect to analysis of the isolates in this study.

Phage type and antimicrobial susceptibility of Salmonella enterica serovar Enteritidis from food-producing animals in Japan between 1976 and 2004.

A total of 56 isolates of Salmonella enterica serovar Enteritidis, including 38 isolates from poultry, 16 from cattle and two from pigs, collected between 1976 and 2004, were subjected to bacteriophage typing and antimicrobial susceptibility testing. Phage type (PT) 8 was predominant in bovine isolates, whereas PT1 and PT4 were predominant in poultry isolates. Resistance was found for 8 of 11 antimicrobials tested, at the following rates: 46.4% for dihydrostreptomycin followed by ampicillin and oxytetracycline (both 8.9%).

The Molecular Detection of Cryptosporidium and Giardia in Sika Deer (Cervus Nippon Centralis) in Japan.

Fecal specimens (271 samples) from wild deer, Cervus nippon centralis, were collected from nine different areas in Japan; these samples were subjected to a real-time reverse transcription PCR for Cryptosporidium-and Giardia-specific 18S ribosomal RNA to investigate the prevalence of Cryptosporidium and Giardia infection. The incidence of Cryptosporidium and Giardia in the nine areas ranged from 0% to 20.0% and 0% to 3.4%, respectively. The prevalence of Cryptosporidium among male and female deer was 8.1% and 3.9%, respectively, while that of Giardia was 0.7% and 0.8%. Sequence analysis identified the Cryptosporidium deer genotype, Cryptosporidium bovis, Cryptosporidium ryanae and Cryptosporidium meleagridis from the sequence of Cryptosporidium-specific partial 18S ribosomal RNA and Giardia intestinalis assemblage A from the partial sequence of Giardia-specific 18S rRNA. The variation in regional prevalence indicates that Cryptosporidium infection depends on environmental factors, and that bovine Cryptosporidium was detected more frequently than cervine Cryptosporidium. These data suggest that wild deer might be a healthy carrier of bovine Cryptosporidium.