Global population structure, genomic diversity and carbohydrate fermentation characteristics of clonal complex 119 (CC119), an understudied Shiga toxin-producing E. coli (STEC) lineage including O165:H25 and O172:H25

Among Shiga toxin (Stx)-producing Escherichia coli (STEC) strains of various serotypes, O157:H7 and five major non-O157 STEC (O26:H11, O111:H8, O103:H2, O121:H19 and O145:H28) can be selectively isolated by using tellurite-containing media. While human infections by O165:H25 STEC strains have been reported worldwide, their detection and isolation are not easy, as they are not resistant to tellurite. Systematic whole-genome sequencing (WGS) analyses have not yet been conducted. Here, we defined O165:H25 strains and their close relatives, including O172:H25 strains, as clonal complex 119 (CC119) and performed a global WGS analysis of the major lineage of CC119, called CC119 sensu stricto (CC119ss), by using 202 CC119ss strains, including 90 strains sequenced in this study. Detailed comparisons of 13 closed genomes, including 7 obtained in this study, and systematic analyses of Stx phage genomes in 50 strains covering the entire CC119ss lineage, were also conducted. These analyses revealed that the Stx2a phage, the locus of enterocyte effacement (LEE) encoding a type III secretion system (T3SS), many prophages encoding T3SS effectors, and the virulence plasmid were acquired by the common ancestor of CC119ss and have been stably maintained in this lineage, while unusual exchanges of Stx1a and Stx2c phages were found at a single integration site. Although the genome sequences of Stx2a phages were highly conserved, CC119ss strains exhibited notable variation in Stx2 production levels. Further analyses revealed the lack of SpLE1-like elements carrying the tellurite resistance genes in CC119ss and defects in rhamnose, sucrose, salicin and dulcitol fermentation. The genetic backgrounds underlying these defects were also clarified.

The global population structure and evolutionary history of the acquisition of major virulence factor-encoding genetic elements in Shiga toxin-producing Escherichia coli O121:H19

Shiga toxin (Stx)-producing Escherichia coli (STEC) are foodborne pathogens causing serious diseases, such as haemorrhagic colitis and haemolytic uraemic syndrome. Although O157:H7 STEC strains have been the most prevalent, incidences of STEC infections by several other serotypes have recently increased. O121:H19 STEC is one of these major non-O157 STECs, but systematic whole genome sequence (WGS) analyses have not yet been conducted on this STEC. Here, we performed a global WGS analysis of 638 O121:H19 strains, including 143 sequenced in this study, and a detailed comparison of 11 complete genomes, including four obtained in this study. By serotype-wide WGS analysis, we found that O121:H19 strains were divided into four lineages, including major and second major lineages (named L1 and L3, respectively), and that the locus of enterocyte effacement (LEE) encoding a type III secretion system (T3SS) was acquired by the common ancestor of O121:H19. Analyses of 11 complete genomes belonging to L1 or L3 revealed remarkable interlineage differences in the prophage pool and prophage-encoded T3SS effector repertoire, independent acquisition of virulence plasmids by the two lineages, and high conservation in the prophage repertoire, including that for Stx2a phages in lineage L1. Further sequence determination of complete Stx2a phage genomes of 49 strains confirmed that Stx2a phages in lineage L1 are highly conserved short-tailed phages, while those in lineage L3 are long-tailed lambda-like phages with notable genomic diversity, suggesting that an Stx2a phage was acquired by the common ancestor of L1 and has been stably maintained. Consistent with these genomic features of Stx2a phages, most lineage L1 strains produced much higher levels of Stx2a than lineage L3 strains. Altogether, this study provides a global phylogenetic overview of O121:H19 STEC and shows the interlineage genomic differences and the highly conserved genomic features of the major lineage within this serotype of STEC.

Differential dynamics and impacts of prophages and plasmids on the pangenome and virulence factor repertoires of Shiga toxin-producing Escherichia coli O145:H28

Phages and plasmids play important roles in bacterial evolution and diversification. Although many draft genomes have been generated, phage and plasmid genomes are usually fragmented, limiting our understanding of their dynamics. Here, we performed a systematic analysis of 239 draft genomes and 7 complete genomes of Shiga toxin (Stx)-producing Escherichia coli O145:H28, the major virulence factors of which are encoded by prophages (PPs) or plasmids. The results indicated that PPs are more stably maintained than plasmids. A set of ancestrally acquired PPs was well conserved, while various PPs, including Stx phages, were acquired by multiple sublineages. In contrast, gains and losses of a wide range of plasmids have frequently occurred across the O145:H28 lineage, and only the virulence plasmid was well conserved. The different dynamics of PPs and plasmids have differentially impacted the pangenome of O145:H28, with high proportions of PP- and plasmid-associated genes in the variably present and rare gene fractions, respectively. The dynamics of PPs and plasmids have also strongly impacted virulence gene repertoires, such as the highly variable distribution of stx genes and the high conservation of a set of type III secretion effectors, which probably represents the core effectors of O145:H28 and the genes on the virulence plasmid in the entire O145:H28 population. These results provide detailed insights into the dynamics of PPs and plasmids, and show the application of genomic analyses using a large set of draft genomes and appropriately selected complete genomes.

[Molecular Characterization of Salmonella enterica subsp. enterica Serovar 4: b: -]

Salmonella is a major causative agent of food borne diseases. Recently, monophasic strains of Salmonella, such as S. enterica 4: i: -, have been frequently reported. Here, we investigated the genetic background of S. enterica 4: b: - using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis. A total of 10 strains of S. enterica (I) 4: b: - were examined and compared with 34 strains including serovar Paratyphi B and Paratyphi B var Java, Schleissheim, and II b: -. All I 4: b: - strains were negative for hin which encodes an invertase that converts the H phases, and six were also negative for fljB, which encodes the second phase of the H antigen. An MLST analysis identified 12 sequence types (ST) and 6 ST complexes (STC) from the 44 strains. A clustering analysis of PFGE patterns almost corresponded to the STC. The monophasic I 4: b: - strains were assigned to 3 STCs (19, 32 and 155), corresponding to those of Paratyphi B var. Java or a monophasic strain according to the data of this and previous studies. These findings suggest that the monophasic strains examined in this study might have been derived from multiple clones of Paratyphi B var Java. This study shows the usefulness of molecular typing as complementation tools of the conventional serotyping system.

Prevalence and Characteristics of Salmonella and Campylobacter in Retail Poultry Meat in Japan

This study was performed to determine the prevalence, antimicrobial susceptibility, and genetic relatedness of Salmonella enterica subsp. enterica and Campylobacter spp. in poultry meat, and to analyze the association of genetic types of these bacteria with their geographical distribution and antimicrobial resistance profiles. Salmonella and Campylobacter isolates have been detected, respectively, in 54 and 71 samples out of 100 samples tested. Nine Salmonella serotypes were found, including S. enterica subsp. enterica serovar Infantis (33%), Schwarzengrund (12%), Manhattan (9%), and others. Campylobacter jejuni and C. coli were detected in 64 (64%) and 14 (14%) samples, respectively. S. enterica subsp. enterica isolates were very frequently resistant to tetracycline (78.3%) and streptomycin (68.3%). Many C. jejuni and C. coli isolates were resistant to sulfamethoxazole/trimethoprim (90.5%), nalidixic acid (47.3%), ampicillin (45.9%), and ciprofloxacin (40.5%). Cluster analysis was performed for the Salmonella isolates using pulsed-field gel electrophoresis (PFGE) data. For Campylobacter isolates, the cluster analysis was based on both PFGE and comparative genomic fingerprinting. The molecular typing results were compared with the information about antimicrobial resistance and geographical locations in which the poultry meat was produced. This analysis revealed that C. jejuni strains with a particular genotype and antimicrobial resistance profile are spreading in specific areas of Japan.

Association between aggregative adherence fimbriae types including putative new variants and virulence-related genes and clump formation among aggR-positive Escherichia coli strains isolated in Thailand and Japan

Enteroaggregative Escherichia coli (EAggEC) are an important cause of diarrhea. Four types of AAF have been identified; however, their prevalence and association with virulence properties remain unclear. E. coli strains carrying the aggR gene as EAggEC that were isolated in Japan and Thailand (n = 90) were examined for AAF subunit genes, two toxin genes (pet/astA), and clump formation. The most prevalent AAF gene was hdaA (28%), followed by aafA (20%), aggA (12%), and agg3A (4%), as well as a putative new AAF sequence (25.6%). Retention status of the toxin genes and intensities of clump formation appeared to vary according to the AAF type.

Increase in resistance to extended-spectrum cephalosporins in Salmonella isolated from retail chicken products in Japan

Extended-spectrum β-lactamase (ESBL)-producing Salmonella are one of the most important public health problems in developed countries. ESBL-producing Salmonella strains have been isolated from humans in Asian countries neighboring Japan, along with strains harboring the plasmid-mediated extended-spectrum cephalosporin (ESC)-resistance gene, ampC (pAmpC). However, only a few studies have investigated the prevalence of ESC-resistant Salmonella in chicken products in Japan, which are the main vehicle of Salmonella transmission. The aim of this study was to investigate the prevalence of ESBL-producing, pAmpC-harboring, or carbapenem-resistant Salmonella in chicken products in Japan. In total, 355 out of 779 (45.6%) chicken product samples collected from 1996–2010 contained Salmonella, resulting in 378 distinct isolates. Of these isolates, 373 were tested for resistance to ESCs, cephamycins, or carbapenems. Isolates that showed resistance to one or more of these antimicrobials were then examined by PCR and DNA sequence analysis for the presence of the bla_CMY, bla_CTX-M, bla_TEM, and bla_SHV resistance genes. Thirty-five resistant isolates were detected, including 26 isolates that contained pAmpC (bla_CMY-2), and nine ESBL-producing isolates harboring bla_CTX-M (n = 4, consisting of two bla_CTX-M-2 and two bla_CTX-M-15 genes), bla_TEM (n = 4, consisting of one bla_TEM-20 and three bla_TEM-52 genes), and bla_SHV (n = 1, bla_SHV-12). All pAmpC-harboring and ESBL-producing Salmonella isolates were obtained from samples collected after 2005, and the percentage of resistant isolates increased significantly from 0% in 2004 to 27.9% in 2010 (P for trend = 0.006). This increase was caused in part by an increase in the number of Salmonella enterica subsp. enterica serovar Infantis strains harboring an approximately 280-kb plasmid containing bla_CMY-2 in proximity to ISEcp1. The dissemination of ESC-resistant Salmonella containing plasmid-mediated bla_CMY-2 in chicken products indicates the need for the development of continuous monitoring strategies in the interests of public health.

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.

Determination of enterohemorrhagic Escherichia coli serotype O165:HNM infection in a hemolytic uremic syndrome patient with adenovirus seroype 41

A 4-year-old girl who was positive for adenovirus according to a rapid immunochromatographic test conducted at a hospital, progressed to hemorrhagic diarrhea and hemolytic uremic syndrome (HUS). The presence of adenovirus serotype 41 (AdV-41) was confirmed by TaqMan real-time PCR and sequence analysis. However, most enteric viral infections cause mild to moderate diarrhea. In the present case, enterohemorrhagic Escherichia coli (EHEC) O165:HNM was isolated concomitantly with AdV-41. In addition, O165 antibody was specifically detected in patient sera. The EHEC isolate was positive for the virulence genes stx1, stx2a, eae type ε, ehxA, and norV. Therefore, we concluded that EHEC O165:HNM was the precise pathogen leading to HUS in this patient.

Virulence gene profiling of enteroaggregative Escherichia coli heat-stable enterotoxin 1-harboring E. coli (EAST1EC) derived from sporadic diarrheal patients

Between 2007 and 2009, a total of 2168 Escherichia coli strains derived from diarrheal patients, defined as putative diarrheagenic E. coli (DEC), were collected from medical institutions in Akita prefecture, Japan. Thirty five of the strains lacked typical pathogenic determinants of DEC other than astA, which encodes enteroaggregative E. coli (EAggEC) heat-stable enterotoxin 1 (EAST1). These E. coli strains are referred to as EAST1EC. Several studies have suggested a role of EAST1 in diarrhea; however, the correlation between diarrhea and the presence of astA remains inconclusive. To investigate whether EAST1EC strains derived from diarrheal patients shared pathogenic factors other than EAST1, virulence gene profiling of 12 virulence genes - iha, lpfA, ldaG, pilS, pic, pet, irp2, daa, aah, aid, cdtB and hlyA - was carried out. PCR analysis revealed that four of the 35 EAST1EC strains harbored only astA, 24 harbored genes associated with adhesins and intestinal colonization, three strains harbored the gene for α-hemolysin, and 24 strains harbored the gene for a siderophore. These results indicated that some EAST1EC strains harbor various virulence genes associated with distinct E. coli pathotypes, primarily enterohemorrhagic E. coli and EAggEC, which may represent additional pathogenic determinants of EAST1EC.

Application of a multilocus variable number of tandem repeats analysis to regional outbreak surveillance of Enterohemorrhagic Escherichia coli O157:H7 infections

A total of 18 strains of EHEC O157:H7 were isolated from distinct cases in Akita Prefecture, Japan from July to September 2007. The genetic relatedness of these isolates was investigated by performing a multilocus variable number of tandem repeats analysis (MLVA) and a pulsed-field gel electrophoresis (PFGE) analysis using XbaI. The PFGE analyses allowed us to group these 18 isolates into three major clusters. The MLVA results correlated closely with those obtained by PFGE, although some variants were found within the clusters obtained by PFGE, thus highlighting the utility of this technique for determining a precise classification when it is difficult to differentiate between isolates with indistinguishable or very similar PFGE patterns. In addition, MLVA is a much easier and more rapid method than PFGE for analysis of the genetic relatedness of strains. Thus, as a second molecular epidemiological subtyping method, MLVA is useful for the regional outbreak surveillance of EHEC O157:H7 infections.

Classification of perA sequences and their correlation with autoaggregation in typical enteropathogenic Escherichia coli isolates collected in Japan and Thailand

Enteropathogenic Escherichia coli (EPEC) strains produce a bundle-forming pilus (BFP) that mediates localized adherence (LA) to intestinal epithelial cells. The major structural subunit of the BFP is bundlin, which is encoded by the bfpA gene located on a large EAF plasmid. The perA gene has been shown to activate genes within the bfp operon. We analyzed perA gene polymorphism among typical (eae- and bfpA-positive) EPEC strains isolated from healthy and diarrheal persons in Japan (n=27) and Thailand (n=26) during the period 1995 to 2007 and compared this with virulence and phenotypic characteristics. Eight genotypes of perA were identified by heteroduplex mobility assay (HMA). The strains isolated in Thailand showed strong autoaggregation and had an intact perA, while most of those isolated in Japan showed weak or no autoaggregation, and had a truncated perA due to frameshift mutation. The degree of autoaggregation was well correlated with adherence to HEp-2 cells, contact hemolysis and BFP expression. Our results showed that functional deficiency due to frameshift mutation and subsequent nonsense mutation in perA reduced BFP expression in typical EPEC strains isolated in Japan.

[The risk of pertussis and diphtheria infections among pediatric healthcare workers in Japan]

For infection control in pediatric hospitals, we investigated the risk of pertussis and diphtheria infections among pediatric healthcare workers. Forty-nine Japanese pediatric healthcare workers in 12 general hospitals were screened for antibodies of pertussis toxin (PT), filamentous hemagglutinin (FHA), and diphtheria toxin (DT). The seropositive rates of anti-PT IgG (protective level, > 10 U/mL), anti-FHA IgG (> 10 U/ mL), and anti-DT (> 0.11 U/mL) were 50, 82, and 59%, respectively. During this survey period (Oct. 2003-Feb. 2004), 16 (33%) of the healthcare workers were in contact with pertussis-infant (s). However, all culture and PCR tests for Bordetella pertussis were negative. One of the 16 exposed healthcare workers, a male pediatrician, had serological evidence of a pertussis infection, but no disease symptomatic of pertussis. Our observations indicate that i) 50 and 41% of Japanese pediatric healthcare workers were seronegative for pertussis (anti-PT IgG) and diphtheria antibodies, respectively, and ii) although the healthcare workers had a high rate of contact with pertussis-infant (s), the infection rate was low. For pertussis and diphtheria infection control in pediatric hospitals, it is important for healthcare workers to be aware of their own protection levels against these diseases.

Intimin types determined by heteroduplex mobility assay of intimin gene (eae)-positive Escherichia coli strains

We developed a quick genetic approach to screen variants of the intimin gene (eae) by using a heteroduplex mobility assay (HMA) that targets the 5' conserved region of eae. The eae variants were categorized into 4 major HMA types and 10 minor subtypes.

[Development of O-serogroup serodiagnosis for patients with hemolytic uremic syndrome by Ec-LPS array]

We extracted lipopolysaccharides from 58 O-serogroup strains of Escherichia coli with phenol-water for use as antigens for an Ec-LPS array. The Ec-LPS array was made by dot-blotting of E. coli LPS on PVDF membrane. Commercial anti-E. coli O-serogroup antisera reacted with homologous O-serogroup LPS in Ec-LPS arrays. Convalescent sera of 6 patients with hemolytic uremic syndrome reacted strongly with O157 LPS when IgM and IgA antibodies in patient sera analyzed by Ec-LPS arrays. When IgG antibody was analyzed in this array, it was difficult to diagnose the O-serogroup because of the reactivity of patient sera against many O-serogroup LPS. These results match those by ELISA and western blotting. Compared to these serological techniques, Ec-LPS array appears superior to ELISA and western blotting in cost performance, time performance, and technical complexity.

Typing of bfpA genes of enteropathogenic Escherichia coli isolated in Thailand and Japan by heteroduplex mobility assay

We developed a rapid genetic approach for screening bfpA variants of enteropathogenic E. coli(EPEC) using a heteroduplex mobility assay (HMA). A total of 204 human EPEC strains were isolated in Thailand and Japan. Of 34 bfpA-positive EPEC strains, bfpA variants were classified into 5 HMA-types. Different HMA-types were found in EPEC of the same serotypes. The results suggest that HMA is a simple and easy method to analyze polymorphism of bfpA gene, and can be used in laboratories without large apparatus such as sequencers.

Nosocomial outbreak of ceftazidime-resistant Serratia marcescens strains that produce a chromosomal AmpC variant with N235K substitution

Serratia marcescens is a Gram-negative bacterium that is often associated with nosocomial infections. Here we analyzed the resistance mechanism of the ceftazidime-resistant S. marcescens nosocomial strains. The five S. marcescens urinary tract infection-associated isolates were positive for chromosomal ampC and bla(TEM-1). Four of the five strains, ES11, ES31, ES42, and ES46, were single clone and ceftazidime resistant. The fifth strain, ES71, was susceptible to ceftazidime. Analysis of the deduced amino acid sequence revealed a Glu-235-Lys substitution in the third amino acid of the third motif of AmpC from both ES46 and ES71, and a site-directed mutagenesis experiment confirmed that this substitution is involved in the ceftazidime resistance phenotype. However, the resistance phenotypes of strains ES46 and ES71 to ceftazidime were quite different from one another, indicating that another mechanism, in addition to the AmpC mutation, is also involved in the determination of the resistance phenotype of these strains. Basal AmpC activity was more than two times higher in strain ES46 than in ES71, which could result in the differing resistance phenotypes of these two strains. The clinical significance and prevalence of extended-spectrum cephalosporin-resistant S. marcescens strains harboring the mutated chromosomal ampC gene are unclear in Japan and remain to be elucidated.

Campylobacter jejuniisolated from retail poultry meat, bovine feces and bile, and human diarrheal samples in Japan: Comparison of serotypes and genotypes

To determine the significance of poultry and bovine as infectious sources of Campylobacter jejuni in Japan, the serotype distribution and pulsed-field gel electrophoresis (PFGE) patterns of poultry and bovine isolates were compared with those of isolates from patients with diarrhea in Akita (Japan). Serotypes O:2 and O:4-complex were common in human, poultry, and bovine isolates, and serotype O:23,36,53 was common in human and bovine isolates. SmaI PFGE patterns of isolates belonging to these serotypes were generated. Eight PFGE patterns were shared by poultry and human isolates and three patterns were shared by human and bovine isolates. Further analysis of the isolates having the same SmaI PFGE pattern by KpnI PFGE confirmed that four patterns and two patterns were still shared by poultry and human isolates, and bovine and human isolates, respectively. Thus, serotypic and genotypic data indicated a possible link between sporadic human campylobacteriosis and C. jejuni from retail poultry and bovine bile and feces, suggesting that bovine serves as an infectious source of C. jejuni in Japan, as is observed in other countries.

Evaluation of pulsed-field gel electrophoresis analysis performed at selected prefectural institutes of public health for use in PulseNet Japan

In order to evaluate reliability of pulsed-field gel electrophoresis (PFGE) analysis performed at different prefectural public health institutes (PHIs) for use in the PulseNet Japan surveillance system to detect enterohemorrhagic Escherichia coli O157, we compared the results of PFGE-typing of 14 selected strains of O157 performed at 8 selected PHIs to evaluate the reliability of different experimental protocols used in these PHIs. PFGE was performed for 14 strains for which there were 14 PFGE types in 3 PHIs, and 13 PFGE types in 5 PHIs by using their own protocols and/or those of the National Institute of Infectious Diseases (NIID). PFGE fingerprints from 5 out of the 8 PHIs were successfully genotyped for all of the 14 strains. A PFGE fingerprint from one PHI was successfully genotyped when the NIID pulsing protocol was used, but was not genotyped when the PHI's own protocols were used. PFGE fingerprints from 2 PHIs failed to be genotyped for one each of the strains. The cause of this genotyping failure was considered to be inappropriate PFGE pulsing protocols or inadequate digestion of chromosomal DNA. These results suggest that PFGE protocols should be standardized for the establishment of PulseNet Japan.

Quantitative Detection ofVibrio vulnificusin Seafood

To quantify the number of Vibrio vulnificus in shellfish, we compared the most probable number (MPN) combined with a culture (MPN-culture) or polymerase-chain reaction (PCR) assay (MPN-PCR) to a quantitative PCR assay. Enrichment in alkaline peptone water by MPN was conducted at 25 and 35 degrees C. Enrichment at 35 degrees C was superior or similar to enrichment at 25 degrees C in over 65% of samples by MPNculture and in more than 75% of samples by MPN-PCR assay. V. vulnificus was more easily isolated on chromogenic agar medium during culture, MPN-PCR assay was superior or similar to MPNculture in over 90% of samples by enrichment at 25 degrees C and to over 88% of samples by enrichment at 35 degrees C. The number of V. vulnificus by quantitative PCR assay was similar to that of MPN-PCR assay in 6 of 8 samples but not from MPNculture. V. vulnificus contamination was frequently detected in samples from Kyushu Island.

Class 1 integron containing metallo-beta-lactamase gene blaVIM-2 in Pseudomonas aeruginosa clinical strains isolated in Japan

Four bla(VIM-2) gene-harboring Pseudomonas aeruginosa strains were identified. These strains possessed a class 1 integron harboring ORF1, bla(VIM-2), and aacA4 gene cassettes. The transposon-mediated horizontal spread of the bla(VIM-2) gene among these strains was suggested, which increases the threat that the bla(VIM-2) gene will disseminate among diverse genera of bacteria.

Prevalence of pandemic thermostable direct hemolysin-producing Vibrio parahaemolyticus O3:K6 in seafood and the coastal environment in Japan

Although thermostable direct hemolysin (TDH)-producing Vibrio parahaemolyticus has caused many infections in Asian countries, the United States, and other countries, it has been difficult to detect the same pathogen in seafoods and other environmental samples. In this study, we detected and enumerated tdh gene-positive V. parahaemolyticus in Japanese seafoods with a tdh-specific PCR method, a chromogenic agar medium, and a most-probable-number method. The tdh gene was detected in 33 of 329 seafood samples (10.0%). The number of tdh-positive V. parahaemolyticus ranged from <3 to 93/10 g. The incidence of tdh-positive V. parahaemolyticus tended to be high in samples contaminated with relatively high levels of total V. parahaemolyticus. TDH-producing strains of V. parahaemolyticus were isolated from 11 of 33 tdh-positive samples (short-necked clam, hen clam, and rock oyster). TDH-producing strains of V. parahaemolyticus were also isolated from the sediments of rivers near the coast in Japan. Representative strains of the seafood and sediment isolates were examined for the O:K serovar and by the PCR method specific to the pandemic clone and arbitrarily primed PCR and pulsed-field gel electrophoresis techniques. The results indicated that most O3:K6 tdh-positive strains belonged to the pandemic O3:K6 clone and suggested that serovariation took place in the Japanese environment.

Characterization of atypical enteropathogenic Escherichia coli strains harboring the astA gene that were associated with a waterborne outbreak of diarrhea in Japan

The virulence traits of the Escherichia coli strain associated with a waterborne diarrhea outbreak were examined. Forty-one of 75 students (ages 12 to 15) in Akita Prefecture, Japan, showed clinical symptoms. Seven E. coli Ouk:K-:H45 isolates were isolated from the patients as the causative agent of this outbreak. One isolate (EC-3605) showed the presence of E. coli attaching-and-effacing (eaeA) and enteroaggregative E. coli heat-stable enterotoxin-1 (astA) genes and the absence of Shiga toxin (stx1 and stx2) genes. A polymorphic enteropathogenic E. coli (EPEC) adherence factor plasmid was detected in EC-3605 with a major structural gene deletion and a regulatory gene frameshift mutation, revealing that EC-3605 represents an atypical EPEC strain harboring the astA gene. The role that atypical EPEC strains harboring the astA gene play in human disease is unclear. Our results, along with those of others, present a possibility that these strains comprise a distinct category of diarrheagenic E. coli and that astA affects the age distribution of atypical-EPEC infection.

[Typings of Campylobacter jejuni isolated from patients of 2 outbreak cases by genotypic and phenotypic methods]

We compared Campylobacter jejuni strains isolated from the patient stools associated with two food-borne diarrheal outbreak cases by the serotypic methods (Lior and Penner systems) and the genotypic methods (restriction fragment length polymorphism (RFLP) of flaA gene and pulsed-field gel electrophoresis (PFGE)). Fla-RFLP was based on the digestion of 410 bp DNA fragment by MboI restriction enzyme amplified from a 5' portion of C. jejuni flaA gene. Six distinctive fla-RFLP patterns were identified by examining 29 serotype reference strains and 58 strains isolated from the patients infected with C. jejuni independently. In the first outbreak case, 4 isolates were shown to be the same patterns each other by the fla-RFLP and PFGE, and by the Lior serotyping, except the Penner system that serotyped into 2 distinct types. On the other hand, in the second case, out of 10 isolates, 5 isolates were identical by the both genotypic and the both serotypic methods, and 4 isolates were not differentiated by the fla-RFLP and Penner system, but were separated into 4 types by PFGE in a little difference. The rest isolate was completely different from the other isolates by the all of methods used now. The findings suggest that the second case occurred by the infection of at least 3 different strains of C. jejuni.

Characterization of enteropathogenic and enteroaggregative Escherichia coli isolated from diarrheal outbreaks

Virulence characteristics of diarrheal outbreak-associated Escherichia coli O55:NM, O126:NM, and O111:NM were examined. The E. coli O55:NM strains were atypical enteropathogenic E. coli (EPEC), while the E. coli O126:NM and O111:NM strains should be classified as enteroaggregative E. coli (EAggEC). The contributions of EPEC and EAggEC to the human disease burden in Japan might be significantly greater than is currently appreciated.

[Characterization of enterohemorrhagic Escherichia coli O26 and development of its isolation media]

We studied 101 strains of Enterohemorrhagic Escherichia coli (EHEC) O26 isolated from diarrhea patients in six prefectural institutes of public health in Japan during June 1996 and December 1997 and tried to establish an isolation medium for EHEC O26. None of the 101 EHEC O26 strains fermented rhamnose; Whereas all of the other EHEC including O157 and non-EHEC (166 strains) fermented rhamnose except 1 strain of non-EHEC. All of the randomly selected EHEC O26 (14 strains of O26:H11.2 strains of O26:H-) showed a very high resistance to potassium tellurite (Minimal Inhibitory Concentration (MIC) > or = 50 micrograms/ml), whereas all of the randomly selected non-EHEC (26 strains) but 1 showed a high sensitivity (MIC < or = 6.25 micrograms/ml) to this compound. On the basis of these results, we developed a Rhamnose MacConkey (RMAC) medium in which lactose in the MacConkey medium was replaced by rhamnose, and Cefixime-Potassium Tellurite-RMAC (CT-RMAC) medium in which Cefixime (0.05mg/l) and Potassium Tellurite (25mg/l) was added to RMAC for the isolation of EHEC O26 strains. We then evaluated the specifcity of these selective media by growing a selected number of O26 (24 strains) and 9 selected strains of bacteria. All of the EHEC O26 strains generated rhamnose non-fermented colonies (white color) on both media. In contrast to the EHEC O26, the vast majority of E. coli strains (166/167 = 99.4%) other than EHEC O26 were theoretically assumed to generate red colonies on the RMAC medium because of their rhamnose fermenting character and most of them were assumed not to grow on CT-RMAC medium because of their sensitivity to potassium tellurite. These findings and results indicate that EHEC O26 can be easily distinguished from other strains of E. coli including O157. Although EHEC O26 strains showed somewhat poor growth on CT-RMAC medium compared with that on RMAC medium, these O26 showed almost the same degree of growth on CT-RMAC as they showed on DHL media. The results of the present study demonstrated that the use of RMAC and CT-MRAC media for the isolation of EHEC O26 is very reliable and efficient with RMAC having good sensitivity and CT-RMAC having a better specificity for the isolation of this strain of EHEC.

[Epidemiological characteristics and virulence factor of verotoxin-producing Eschericia coli O121:H19 isolated in Akita Prefecture in July 1997]

Epidemiological characteristics and virulence factors of VTEC O121:H19 strains isolated in July 1997 from a 15 year old female and a 20 year old male patient suffering from bloody diarrhea and severe abdominal pain were examined. The 2 VTEC O121:H19 isolates showed identical antibiotic susceptibility patterns, biochemical characteristics and plasmid profile while slight differences were observed in their Xba I and Not I PFGE patterns, suggesting that closely related 2 VTEC O121:H19 strains evoked the sporadic infectious cases in July 1997. The 2 VTEC O121:H19 isolates, as well as VTEC O157:H7, possessed eaeA gene and a ca. 60 MDa plasmid which hybridised with CVD 419 probe and produced enterohemolysin. In addition, the VTEC O121:H19 isolates produced almost the same amount of VT-2 in vitro as VTEC O157:H7 did. These results suggested that VTEC O121:H19 possesed the virulence factor comparable to that of VTEC O157:H7. Incidence, molecular epidemiology and infectious source of VTEC O121:H19 in this country have not been sufficiently understood. Antiserum for E. coli serogroup O121 should be manufactured to clarify the epidemiology of the highly virulent VTEC strain.

[A familial outbreak of verotoxin-producing Escherichia coli O103:H2 infection in which a calf was the suspected infectious source]

A familial outbreak of Verotoxin-producing Escherichia coli (VTEC) infection occurred in July 1996 in AKITA prefecture. Four VTEC strains harboring VT-1 and eaeA genes were isolated from three patients and a calf, breeding farm for which was located as close as 4 meters from the house where the patients lived in. All of the 4 VTEC isolates were serotyped as O63:H2 using commercially available sera kits. However, a patient isolate, EC-281, was serotyped as 0103:H2 at the International Escherichia and Klebsiella Centre. Titration and absorption tests using rabbit antisera raised against EC-281 confirmed that the serogroup of the remaining 3-VTEC isolates was also O103. Epidemiological characteristics including plasmid profile, antibiotic susceptibility patterns and pulsed-field gel electrophoresis patterns of the 4 VTEC isolates were completely the same, indicating that these isolates originated from a common source. These findings in conjunction with the results of epidemiological survey conducted by the Health Center suggested that a possible infectious source for this outbreak is the calf. Our present results strengthen the significance of calf as an infectious source of VTEC infection.

[Characteristics of enterotoxigenic Escherichia coli and E. coli harboring enteroaggregative E. coli heat-stable enterotoxin-1 (EAST-1) gene isolated from a water-borne outbreak]

A water-borne outbreak occurred in A Town in Akita prefecture on March 1995. Enterotoxigenic Escherichia coli (ETEC) strains were isolated from 6 of 13 feces of patients with food poisoning disease and from 1 of 4 drinking water samples. In addition, E. coli strains harboring Enteroaggregative E. coli (EAggEC) heat-stable enterotoxin-1 (EAST-1) gene were isolated from 5 of 13 patient's feces and 1 feces sample obtained from the septic tank. Both of the E. coli strains were isolated from the 3 patient's feces, suggesting that this outbreak was a mixed infectious case. All of the ETEC strains possessed both heat-stable enterotoxin (ST) and EAST-1 genes and their serotype was O148:H28. The EAST-1 gene was detected on a ca. 80 kb plasmid by a southern blot analysis using EAST-1 DNA probe in the 5 of 7 ETEC strains. The southern blot analysis suggested that the location of the EAST-1 gene was genome in the rest of the 2 ETEC strains. A southern blot analysis using ST DNA probe also suggested that the location of the ST gene was genome in all of the ETEC strains. On the other hand, all of the 6 E. coli strains harboring EAST-1 gene could not be serotyped with commercially available OH sera. The location of the EAST-1 gene in all of the isolates was suggested to be genome by the southern blot analysis. All of the isolates lacked aggA gene which has been demonstrated to be involved in expression of aggregative adherence phenotype in EAggEC, suggesting that the EAST-1 gene-harboring strains isolated in this case were distinct from EAggEC. These results indicated that the EAST-1 gene was also harbored by E. coli strains distinct from EAggEC. In addition, a possibility was also suggested that the EAST-1 gene might be a transposon, as well as ST gene. Further study should be conducted in order to elucidate the significance of EAST-1 as a vilurence factor of diarrheagenic E. coli.

[Enteropathogenic Escherichia coli strains harboring enteroaggregative Escherichia coli (EAggEC) heat-stable enterotoxin-1 gene isolated from a food-borne like outbreak]

A food-poisoning outbreak occurred in G Town in Minami-Akita District, Akita Prefecture on 16 January 1995. As the causative agent of the outbreak, Enteropathogenic Escherichia coli (EPEC) O126:NM were isolated. The isolates showed the same plasmid profile and antibiotic susceptibility patterns suggesting that the EPEC strains originated from same infectious source. The isolates lacked eae and EAF genes which were considered to play a significant role in the diarrheagenic mechanism of EPEC. On the otherhand, the isolates possessed Enteroaggregative E. coli (EAggEC) heat-stable enterotoxin-1 (EAST-1) gene, though they did not possess the agg A gene in which the coded structural subunit of Aggregative adherence fimbriae 1 (AAF/1) has been demonstrated to be involved in the expression of ability for EAggEC to adhere to cultured cells in aggregative pattern, indicating that the EPEC strains apparently differed from EAggEC. These data suggested that EAST-1 showed its enterotoxic activity to human, and that EPEC represented multiple category of E. coli strains with different diarrheagenic mechanism, in which both eae and EAST-1 might be involved.

[Some characteristics of verotoxin-producing Escherichia coli strains isolated from sporadic diarrhea in Akita Prefecture]

Six sporadic cases of VTEC infection have been confirmed in Akita Prefecture from June. 1991 to Nov. 1994. Six VTEC strains isolated in these cases were examined for their serotype, Vero toxin type, existence of eae gene and 60 MDA plasmid, and CVD probe reactivity. Of the 6 isolates, 5 were O157:H7. Two isolates of which possessed TV-1 and VT-2 genes and the rest of 3 possessed VT-1 and VT-2vh genes, VT-2 gene, respectively. One isolate was O26:NM possessing VT-1 gene. A primer pair, designated as EA-1 and EA-2, was designed for detecting eae gene in VTEC. Examination of the 6 VTEC isolates by PCR using EA-1 and EA-2 primers indicated that all of the isolates were eae positive. This was further confirmed by dot blot hybridization using a eae probe. All of the 6 isolates also harbored approximately 60 MDa plasmid, which hybridized with the CVD419 probe in southern blot analysis. These results supported the hypothesis that eae gene and the 60 MDa plasmid might play a role in the mechanism for VTEC to cause diseases including diarrhea, hemorrhagic colitis and hemolytic uremic syndrome in humans. Diversity observed in plasmid profile and VT type of the 6 isolates suggested that they were originated from independent sources, which could not be identified.

[Characterization by RFLP of DNAs from Campylobacter jejuni Lior serotype reference strains and clinical isolates and detection of C. jejuni by DNA-probe]

The Lior serotype reference strains and clinical isolates of Campylobacter jejuni were compared in the restriction fragment length polymorphism (RFLP) pattern to distinguish C. jejuni strains. These reference strains showed RFLP patterns different from one to another, while the patterns of some isolates were not coincident with those of the same serotype reference strains. Furthermore, we tried to hybridize HindIII-digested fragments from these strains with the DNA probe encoding the 46-kDa protein of C. jejuni by Southern and slot blottings. The 1.8-kbp fragments from all strains of C. jejuni hybridized with this probe, but those from other species of Campylobacter or enterobacteria did not. These results indicate that the Lior serotype is unrelated with the RFLP pattern of DNA of C. jejuni strains, but the DNA probe is useful to detect C. jejuni.

Specific detection of Campylobacter jejuni by means of polymerase chain reaction in chicken litter

A routine detection assay of Campylobacter jejuni was developed with the polymerase chain reaction (PCR). A pair of oligonucleotide primers from the flaA of C. jejuni were used in detection by PCR. Although the primer pair specifically detected C. jejuni strains, they did not detect strains of C. coli, C. fetus, Salmonella spp. or Escherichia coli. In litter inoculated with C. jejuni, specific detection of C. jejuni was obtained by PCR with this primer pair.

Inhibition of superoxide generation and of increase in intracellular Ca2+ concentration by zinc in rat neutrophils stimulated with zymosan

The effect of Zn2+ on the O2- generation and change in intracellular Ca2+ concentration ([Ca2+]i) of rat peritoneal neutrophils was studied. Zymosan (serum-treated zymosan (STZ))-induced O2- generation was inhibited by Zn2+ at concentrations as low as 10 microM. A large amount of the inhibition was observed in the absence of extracellular Ca2+ but the inhibition could not be restored by increasing the extracellular Ca2+ concentration, indicating that Zn2+ does not necessarily inhibit the O2- generation competitively with extracellular Ca2+. In the absence of extracellular Ca2+, Zn2+ inhibited STZ-induced transient increase in [Ca2+]i in the concentration range that evoked a marked inhibition in the O2- generation. On the other hand, Zn2+ did not inhibit significantly STZ-induced uptake of 45Ca2+ from extracellular medium by the cells. From these results, it is suggested that Zn2+ inhibits STZ-induced release of Ca2+ from intracellular storage sites, resulting in the suppression of the activation mechanism of neutrophils.

Enhancement of zymosan-induced respiratory burst of rat neutrophils by lead in vitro

The effect of Pb2+ on serum-treated zymosan (STZ)-induced O2 consumption of rat peritoneal neutrophils was studied. Pb2+ was found to mimic effectively the enhancing action of Ca2+ on the O2 consumption depending on the concentration up to about 80 microM. However, at concentrations over 80 microM, Pb2+ inhibited the O2 consumption. The enhancing effect of Pb2+ on the O2 consumption was further examined using the intracellularly Ca2(+)-depleted neutrophils. Pb2+ also enhanced the O2 consumption of the Ca2(+)-depleted cells as effectively as Ca2+. The Pb2(+)-enhanced O2 consumption of the Ca2(+)-depleted cells was inhibited by N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7) based on its calmodulin antagonistic action. The effect of Pb2+ on the activity of activator-deficient 3',5'-cyclic nucleotide phosphodiesterase (PDE), a calmodulin-dependent enzyme, was examined. Pb2+ activated PDE as effectively as Ca2+ only in the presence of calmodulin. The Pb2(+)-activated PDE activity was also inhibited by W-7 only in the presence of calmodulin. These results indicated that Pb2+ could replace Ca2+ in the activation process(es) of the respiratory burst, suggesting a possible involvement of calmodulin in the enhancing mechanism of the O2 consumption by Pb2+.