Phage types and genotypes of Shiga toxin-Producing Escherichia coli O157 in Finland

Genetic diversity among clonal lineages within Escherichia coli O157:H7 stepwise evolutionary model

Molecular characterization and subtyping show genetic diversities within clonal complexes.

Escherichia coli O157:H7 variants were examined for trait mutations and by molecular subtyping to better define clonal complexes postulated on the O157:H7 evolution model. Strains of β-glucuronidase–positive, sorbitol-negative O157:H7 isolated in United States and Japan were identical to A5 clonal strain and shared sequence type (ST)–65 by multilocus sequence typing (MLST); thus, they belong in A5. However, these strains exhibited pulsed-field gel electrophoresis (PFGE) profile differences that suggested genomic divergence between populations. Sorbitol-fermenting O157 (SFO157) strains from Finland, Scotland, and Germany were identical to A4 clonal strain and belong in A4. Some SFO157 strains, isolated years apart and from different countries, had identical PFGE profiles, suggesting a common origin. Despite similarities, some Finnish and Scottish and all of the German strains have ST-75 (“German clone”), whereas others have ST-76, a new variant (“Scottish clone”). MLST of strains in other clonal complexes also discriminated strains thought to be identical and showed that genetic differences will further distinguish clonal populations into subclones.

Phage types, virulence genes and PFGE profiles of Shiga toxin-producing Escherichia coli O157:H7 isolated from raw beef, soft cheese and vegetables in Lima (Peru)

The present study was conducted in Lima Metropolitana to evaluate the prevalence of Shiga toxin-producing Escherichia coli (STEC) O157:H7 in raw beef, raw ground beef, soft cheese and fresh vegetables, sampled at different markets in the city. Between October 2000 and February 2001, 407 food samples were collected from different markets in the 42 districts of Lima Metropolitana. Samples were assayed for E. coli O157 by selective enrichment in modified Tryptic Soy Broth containing novobiocin, followed by immunomagnetic separation (IMS) and plating onto sorbitol MacConkey agar supplemented with cefixime and potassium tellurite. Fifty (12.3%) of 407 food samples resulted positive for E. coli O157 isolation (23 of 102 ground beef; 15 of 102 beef meat; eight of 102 soft cheese and four of 101 fresh vegetables). Thirty-five E. coli O157 isolates were further analysed for the presence of virulence genes. All 35 were positive by PCR for O157 rfbE, fliCh7, eae-gamma1 and ehxA genes. In addition, genes encoding Shiga toxins were detected in 33 of 35 isolates, five isolates (14%) encoded stx(1), stx(2), and 28 (80%) stx2 only. The isolates were of seven different phage types (PT4, PT8, PT14, PT21, PT34, PT54, and PT87) with three phage types accounting for 80% of isolates: PT4 (15 isolates), PT14 (8 isolates), and PT21 (5 isolates). Interestingly, the majority (31 of 35; 89%) of E. coli O157:H7 isolates characterized in this study belonged mainly to the phage types previously found in STEC O157:H7 strains associated with severe human disease in Europe and Canada. Pulsed-field gel electrophoresis (PFGE) of 32 isolates revealed 14 XbaI-PFGE groups (I to XIV) of similarity >85%, with 23 (72%) isolates grouped in five clusters. Some isolates from different districts presented a high clonal relatedness. Thus, PFGE group VIII clustered eleven strains from nine different districts. The broad range of PFGE subtypes found in this study demonstrates the natural occurrence of many genetic variants among STEC O157:H7 spread in Lima.

Molecular and phenotypic profiling of sorbitol-fermenting Escherichia coli O157:H- human isolates from Finland

This study investigated the occurrence of virulence-associated genes, including stx1, stx2, stx2c, stx2d, stx2e, eae and its subtypes (alpha, beta, gamma, epsilon), efa1, cdt-V cluster, enterohaemorrhagic Escherichia coli (EHEC)-hlyA, katP, espP, etpD, sfpA and the flagellar fliC gene, in nine sorbitol-fermenting (SF), beta-glucuronidase-positive E. coli O157:H- (non-motile) isolates obtained from humans in Finland between 1997 and 2001. In addition, the production of Shiga toxin (Stx), cytolethal distending toxin (CDT)-V and EHEC haemolysin (EHEC-Hly) was studied, and the phage type (PT) and pulsed-field gel electrophoresis (PFGE) types were determined. All nine isolates carried eae-gamma, efa1, EHEC-hlyA, etpD, sfpA and fliC; eight also harboured the cdt-V gene cluster and five were positive for stx2. None of the isolates harboured stx1, stx2c, stx2d, stx2e, katP or espP. All isolates harbouring the corresponding genes also produced Stx2 and CDT-V in titres ranging from 1:32 to 1:128 and from 1:2 to 1:4, respectively. None of the isolates expressed EHEC-Hly on enterohaemolysin agar. Seven isolates belonged to PT88 and two had a PT88 variant pattern. Seven isolates showed a close genetic relationship, with a PFGE similarity index (SI) of 92-98%. Two isolates, temporally the first and last, obtained 5 years apart, were the most divergent (SI of 71% and 85%, respectively). The study demonstrated that SF E. coli O157:H- isolates from Finland are closely related and show a close relationship with SF E. coli O157 strains isolated in Germany. This finding suggests a clonality of SF E. coli O157:H- isolates from different geographical regions.

Relatedness of Escherichia coli strains with different susceptibility patterns isolated from beagle dogs during ampicillin treatment

The aim of this study was to investigate the effects of ampicillin treatment on selection and diversity of ampicillin-resistant intestinal Escherichia coli in beagles treated with ampicillin, ampicillin + beta-lactamase (targeted to degrade antibiotic residues in the gut) or placebo. Selected faecal (n = 339) and jejunal (n = 63) E. coli isolates with known resistance patterns were typed using pulsed-field gel electrophoresis (PFGE). Among the 25 detected PFGE types, ampicillin resistance was detected in 6, none of which was dominant over others among the dogs. The resistant types increased especially in the ampicillin group, whilst beta-lactamase inhibited their emergence. Selection of genetically unrelated resistant strains rather than emerging resistance among previously susceptible strains accounts for increasing resistance rates during ampicillin treatment.

Characterization of Shiga toxin-producingEscherichia coliisolated from aquatic environments

This study reports the phenotypic and genotypic characterization of 144 Shiga toxin-producing Escherichia coli (STEC) strains isolated from urban sewage and animal wastewaters using a Shiga toxin 2 gene variant (stx(2))-specific DNA colony hybridization method. All the strains were classified as E. coli and belonged to 34 different serotypes, some of which had not been previously reported to carry the stx(2) genes (O8:H31, O89:H19, O166:H21 and O181:H20). Five stx(2) subtypes (stx(2), stx(2c), stx(2d), stx(2e) and stx(2g)) were detected. The stx(2), stx(2c), stx(2d) and stx(2e) subtypes were present in urban sewage and stx(2e) was the only stx(2) subtype found in pig wastewater samples. The stx(2c) and stx(2g) were more associated with cattle wastewater. One strain was positive for the intimin gene (eae) and five strains of serotypes were positive for the adhesin encoded by the saa gene. A total of 41 different seropathotypes were found. On the basis of occurrence of virulence genes, most non-O157 STEC strains are assumed to be low-virulence serotypes.

Development of a PCR-restriction fragment length polymorphism assay for the epidemiological analysis of Shiga toxin-producing Escherichia coli

Six characteristic regions (I to VI) were identified in Shiga toxin 2 (Stx2) phages (T. Sato, T. Shimizu, M. Watarai, M. Kobayashi, S. Kano, T. Hamabata, Y. Takeda, and S. Yamasaki, Gene 309:35-48, 2003). Region V, which is ca. 10 kb in size and is located in the upstream region of the Stx operons, includes the most distinctive region among six Stx phages whose genome sequences have been determined. In this study, we developed a PCR-restriction fragment length polymorphism (RFLP) assay for the epidemiological analysis of Shiga toxin-producing Escherichia coli (STEC) on the basis of the diversity of region V. When region V was amplified by long and accurate-PCR (LA-PCR) with five control E. coli strains carrying six different Stx phages such as E. coli strains C600 (Stx1 phage), C600 (933W phage), C600 (Stx2 phage-I), C600 (Stx2 phage-II), and O157:H7 Sakai strain RIMD0509952 (VT1-Sakai phage and VT2-Sakai phage), an expected size of the band was obtained. Restriction digest of each PCR product with BglI or EcoRV also gave the expected sizes of banding patterns and discriminated the RFLPs of five control strains. When a total of 204 STEC O157 strains were analyzed by LA-PCR, one to three bands whose sizes ranged from 8.2 to 14 kb were obtained. Two STEC O157 strains, however, did not produce any bands. Subsequent restriction digest of the PCR products with BglI or EcoRV differentiated the RFLPs of 202 STEC O157 strains into 24 groups. The RFLP patterns of pulsed-field gel electrophoresis (PFGE) of representative strains of STEC O157 divided into 24 groups were well correlated with those of PCR-RFLP when STEC O157 strains were isolated in the same time period and in the close geographic area. To evaluate the PCR-RFLP assay developed here, ten strains, each isolated from four different outbreaks in different areas in Japan (Tochigi, Hyogo, Aichi, and Fukuoka prefecture), were examined to determine whether the strains in each group showed the same RFLP patterns in the PCR-RFLP assay. In accordance with the results of PFGE except for strains isolated in an area (Fukuoka), which did not produce any amplicon, ten strains in each group demonstrated the same RFLP pattern. Taken together, these data suggest that the PCR-RFLP based on region V is as useful as PFGE but perhaps more simple and rapid than PFGE for the molecular epidemiological analysis of STEC strains during sporadic and common source outbreaks.

Application of molecular genetic methods in diagnostics and epidemiology of food-borne bacterial pathogens

Salmonella enterica, Campylobacter and Yersinia species, Shiga toxin-producing Escherichia coli (STEC), Listeria monocytogenes and Clostridium perfringens are the bacterial pathogens constituting the greatest burden of food-borne disease in Finland. Several molecular genetic methods have been applied to diagnose, discriminate and survey these bacteria. PCR, PCR-RFLP and PFGE are the most widely and successfully used. However, these methods are unable to replace conventional and internationally standardised phenotyping. Electronic database libraries of the different genomic profiles will enable continuous surveillance of infections and detection of possible infection clusters at an early stage. Furthermore, whole-genome sequence data have opened up new insights into epidemiological surveillance. Laboratory-based surveillance performed in a timely manner and exploiting adequate methods, and co-operation at local, national and international levels are among the key elements in preventing food-borne diseases. This paper reviews different applications of molecular genetic methods for investigating enteric bacterial pathogens and gives examples of the methods successfully used in diagnostics and epidemiological studies in Finland.

Phage types and genotypes of shiga toxin-producing Escherichia coli O157:H7 isolates from humans and animals in spain: identification and characterization of two predominating phage types (PT2 and PT8)

Phage typing and DNA macrorestriction fragment analysis by pulsed-field electrophoresis (PFGE) were used for the epidemiological subtyping of a collection of Shiga toxin-producing Escherichia coli (STEC) O157:H7 strains isolated in Spain between 1980 and 1999. Phage typing distinguished a total of 18 phage types among 171 strains isolated from different sources (67 humans, 82 bovines, 12 ovines, and 10 beef products). However, five phage types, phage type 2 (PT2; 42 strains), PT8 (33 strains), PT14 (14 strains), PT21/28 (11 strains), and PT54 (16 strains), accounted for 68% of the study isolates. PT2 and PT8 were the most frequently found among strains from both humans (51%) and bovines (46%). Interestingly, we detected a significant association between PT2 and PT14 and the presence of acute pathologies. A group of 108 of the 171 strains were analyzed by PFGE, and 53 distinct XbaI macrorestriction patterns were identified, with 38 strains exhibiting unique PFGE patterns. In contrast, phage typing identified 15 different phage types. A total of 66 phage type-PFGE subtype combinations were identified among the 108 strains. PFGE subtyping differentiated between unrelated strains that exhibited the same phage type. The most common phage type-PFGE pattern combinations were PT2-PFGE type 1 (1 human and 11 bovine strains), PT8-PFGE type 8 (2 human, 6 bovine, and 1 beef product strains), PT2-PFGE subtype 4A (1 human, 3 bovine, and 1 beef product strains). Nine (29%) of 31 human strains showed phage type-PFGE pattern combinations that were detected among the bovine strains included in this study, and 26 (38%) of 68 bovine strains produced phage type-PFGE pattern combinations observed among human strains included in this study, confirming that cattle are a major reservoir of strains pathogenic for humans. PT2 and PT8 strains formed two groups which differed from each other in their motilities, stx genotypes, PFGE patterns, and the severity of the illnesses that they caused.

Serotypes and Shiga toxin genotypes among Escherichia coli isolated from animals and food in Argentina and Brazil

Shiga toxin (Stx)-producing Escherichia coli (STEC) strains isolated from animals and food in Argentina (n=44) and Brazil (n=20) were examined and compared in regard to their phenotypic and genotypic characteristics to evaluate their pathogenic potential. The clonal relatedness of STEC O157 isolates (n=22) was established by phage typing (PT) and pulsed-field gel electrophoresis (PFGE). All O157 strains studied carried eae and enterohemorrhagic E. coli (EHEC)-hly sequences. In Argentina, these strains occurred both in cattle and meat, and 50% of them carried stx2/stx2vh-a genes, whereas in Brazil the O157 strains were isolated from animals, and most harbored the stx2vh-a sequence. At least 13 different O:H serotypes were identified among the non-O157 strains studied, with serotype O113:H21 being found in both countries. All but one non-O157 strains did not carry eae gene, but EHEC-hlyA gene was found in 85.7% of them, and the stx2 genotype was also more prevalent in Argentina than in Brazil (P<0.01), where stx1 alone or in association was most common (68.8%). One STEC strain isolated from a calf in Brazil harbored the new variant referred to as stx2-NV206. PFGE analysis showed that STEC O157 strains were grouped in four clusters. One Brazilian strain was considered possibly related (> or =80%) to Argentinean strains of cluster I. Differences in the pathogenic potential, especially in regard to serotypes and stx genotypes, were observed among the STEC strains recovered from animals and food in both countries.

Verotoxin-producing Escherichia coli in Spain: prevalence, serotypes, and virulence genes of O157:H7 and non-O157 VTEC in ruminants, raw beef products, and humans

In Spain, as in many other countries, verotoxin-producing Escherichia coli (VTEC) strains have been frequently isolated from cattle, sheep, and foods. VTEC strains have caused seven outbreaks in Spain (six caused by E. coli O157:H7 and one by E. coli O111:H- [nonmotile]) in recent years. An analysis of the serotypes indicated serological diversity. Among the strains isolated from humans, serotypes O26:H11, O111:H-, and O157:H7 were found to be more prevalent. The most frequently detected serotypes in cattle were O20:H19, O22:H8, O26:H11, O77:H41, O105:H18, O113:H21, O157:H7, O171:H2, and OUT (O untypeable):H19. Different VTEC serotypes (e.g., O5:H-, O6:H10, O91:H-, O117:H-, O128:H-, O128:H2, O146:H8, O146:H21, O156:H-, and OUT:H21) were found more frequently in sheep. These observations suggest a host serotype specificity for some VTEC. Numerous bovine and ovine VTEC serotypes detected in Spain were associated with human illnesses, confirming that ruminants are important reservoirs of pathogenic VTEC. VTEC can produce one or two toxins (VT1 and VT2) that cause human illnesses. These toxins are different proteins encoded by different genes. Another virulence factor expressed by VTEC is the protein intimin that is responsible for intimate attachment of VTEC and effacing lesions in the intestinal mucosa. This virulence factor is encoded by the chromosomal gene eae. The eae gene was found at a much less frequency in bovine (17%) and ovine (5%) than in human (45%) non-O157 VTEC strains. This may support the evidence that the eae gene contributes significantly to the virulence of human VTEC strains and that many animal non-O157 VTEC strains are less pathogenic to humans.

Serology and genetics of the flagellar antigen of Escherichia coli O157:H7a,7c

Among Escherichia coli strains of the O55:H7 serovar, which is considered the ancestor of Shiga toxin-producing E. coli (STEC) O157:H7, two subtypes, H7a,7b and H7a,7c (briefly, H7a,b and H7a,c, respectively), of the H7 flagellar antigen have been described previously [J. Wright and R. Villanueva, J. Hyg. (Camb.) 51:39-48, 1953; Y. A. Ratiner and V. A. Sinelnikova, Zh. Microbiol. Epidemiol. Immunobiol. 3:111-116, 1969). We have now studied 13 STEC O157:H7 strains and 1 O55:H7 strain that were epidemiologically unrelated, that originated from six countries on two continents, and that had different profiles when analyzed by multilocus enzyme electrophoresis, pulsed-field gel electrophoresis, and PCR for stx and eae. They were all found to possess the H7a,c flagellar antigen. Serum cross-absorption assays confirmed that their H antigens were indistinguishable from each other and from that of E. coli O55:H7a,c but differed from the standard H7a,b antigen of E. coli H test strain U5/41. It was shown by phage-mediated transduction that the flagellin genes for these two H-antigen subserotypes were alleles of the E. coli fliC locus. On the basis of the serological data obtained in this study and the molecular characteristics of E. coli fliC(H7) alleles recently published, it is inferred that H7a,c and H7a,b are the main serological subtypes of the group of E. coli H7 flagellins.

Longitudinal study of Escherichia coli O157 in a cattle finishing unit

In a longitudinal study in a Finnish cattle finishing unit we investigated excretion and sources of Escherichia coli O157 in bulls from postweaning until slaughter. Three groups of 31 to 42 calves were sampled in a calf transporter before they entered the farm and four to seven times at approximately monthly intervals at the farm. All calves sampled in the livestock transporter were negative for E. coli O157 on arrival, whereas positive animals were detected 1 day later. During the fattening period the E. coli O157 infection rate varied between 0 and 38.5%. The animals were also found to be shedding during the cold months. E. coli O157 was isolated from samples taken from water cups, floors, and feed passages. E. coli O157 was detected in 9.7 to 38.9% of the fecal samples taken at slaughter, while only two rumen samples and one carcass surface sample were found to be positive. E. coli O157 was isolated from barn surface samples more often when the enrichment time was 6 h than when the enrichment time was 24 h (P < 0.0001). Fecal samples taken at the abattoir had lower counts (< or = 0.4 MPN/g) than fecal samples at the farm (P < 0.05). E. coli O157 was isolated more often from 10-g fecal samples than from 1-g fecal samples (P < 0.0001). Most farm isolates belonged to one pulsed-field gel electrophoresis (PFGE) genotype (79.6%), and the rest belonged to closely related PFGE genotypes. In conclusion, this study indicated that the finishing unit rather than introduction of new cattle was the source of E. coli O157 at the farm and that E. coli O157 seemed to persist well on barn surfaces.

Characteristics and association with disease of two major subclones of Shiga toxin (Verocytotoxin)-producing strains of Escherichia coli (STEC) O157 that are present among isolates from patients in Germany

Shiga toxin (Verocytotoxin) producing E. coli (STEC) O157 were isolated from 168 patients living in different parts of Germany. Most isolates were from sporadic cases and seven small outbreaks with STEC O157 were identified. The 168 strains were examined for phenotypic and genotypical traits in order to identify major types of STEC O157 occurring in Germany. Phage typing (PT) revealed PT8 (n = 54) and PT2 (n = 48) strains as most frequent (60.7%) among the isolates. Carriage of the stx(2) gene by STEC O157 was closely associated with hemolytic uremic syndrome (100%) and with bloody diarrhea (61.7%). The stx(2) gene was frequent in PT88, PT47 (both 100%), PT2 (91.5%) and PT4 (87.5%) strains and more rarely (33.3%) found in strains belonging to the other PTs. PT8 and PT2 strains formed two groups which differed from each other in their motility, stx-genotypes and the severity of the illness they caused. Pulsed-field gel electrophoresis of PT2 and PT8 strains and hybridization of XbaI digested DNA with stx(1) and stx(2) specific gene probes revealed similarities among epidemiologically unrelated strains belonging to the same PT. The results indicate that STEC O157 PT2 and PT8 strains form two distinct subclones which are dominating in Germany and other European countries.

Clinical Escherichia coli strains carrying stx genes: stx variants and stx-positive virulence profiles

Altogether, 173 Shiga toxin-producing Escherichia coli (STEC) serotype O157 (n = 111) and non-O157 (n = 62) isolates from 170 subjects were screened by PCR-restriction fragment length polymorphism for eight different stx genes. The results were compiled according to serotypes, phage types of O157, production of Stx toxin and enterohemolysin, and the presence of eae. The stx genes occurred in 11 combinations; the most common were stx(2) with stx(2c) (42%), stx(2) alone (21%), and stx(1) alone (16%). Of the O157 strains, 64% carried stx(2) with stx(2c) versus 2% of the non-O157 strains (P < 0.001). In the non-O157 strains, the prevailing gene was stx(1) (99% versus 1% in O157 strains; P < 0.001). In addition, one strain (O Rough:H4:stx(2c)) which has not previously been described as associated with hemolytic-uremic syndrome (HUS) was found. Ten stx-positive virulence profiles were responsible for 71% of all STEC infections. Of these profiles, five accounted for 71% of the 21 strains isolated from 20 patients with HUS or thrombotic thrombocytopenic purpura (TTP). The strains having the virulence profile that caused mainly HUS or TTP or bloody diarrhea produced Stx with titers of >/=1:128 (90%) more commonly than did other strains (51%; P < 0.001). These strains were also more commonly enterohemolytic (98% versus 68% for other strains; P < 0.001) and possessed the eae gene (100%) more commonly than did other strains (74%; P < 0.001). A particular virulence profile, O157:H7:PT2:stx(2):stx(2c):eae:Ehly, was significantly more frequently associated with HUS and bloody diarrhea than were other profiles (P = 0.02) and also caused the deaths of two children. In this study, the risk factors for severe symptoms were an age of <5 years and infection by the strain of O157:H7:PT2 mentioned above.

Characterisation of Escherichia coli O157 isolates from Danish cattle and human patients by genotyping and presence and variants of virulence genes

Escherichia coli O157 isolates obtained from 17 Danish cattle herds and from a national surveillance programme of cattle at slaughter were genotyped by pulsed-field gel electrophoresis (PFGE) and characterised with respect to presence of and variation in virulence factors. The characteristics of the cattle strains were compared to human clinical isolates from the same time period. All verocytotoxin (VT)-producing E. coli O157 (VTEC O157) from cattle possessed all typical VTEC O157:H7 virulence factors and had either the VT2c-variant alone or together with VT1. Among human isolates the dominant toxin profile was VT2 + VT2c. Only one PFGE group was represented on each farm, indicating that introduction and establishment of new E. coli O157 strains to these cattle farms is probably not common. Among E. coli O157 isolates from cattle, 22.8% were not VT-producing. The majority of these possessed the eae gene and all other genotypic and phenotypic traits typical for E. coli O157:H7. On the basis of the virulence characteristics, it is concluded that the VTEC O157 strains isolated from Danish cattle are potential human pathogens. However, the observed differences between cattle and human isolates with regard to VT-profile, genotype and antimicrobial resistance could be important, i.e. either Danish cattle might not be the most important reservoir for human infections or Danish cattle mostly harbour VTEC O157 isolates that are less likely to cause human disease.

Clinical isolates of non-O157 Shiga toxin-producing Escherichia coli: serotypes, virulence characteristics, and molecular profiles of strains of the same serotype

All human Shiga toxin-producing Escherichia coli (STEC) non-O157 strains (n = 56) isolated in Finland from 1990 to August 2000 were characterized for the O:H serotype, stx(1) and stx(2) genes, production of enterohemolysin, and sensitivity to 12 antimicrobial agents. Strains of the same serotype were genotyped by pulsed-field gel electrophoresis (PFGE) after XbaI restriction of total DNA. The 56 non-O157 isolates belonged to 29 serotypes. Two of the serotypes (O102:H7 and OX181:H49) have not previously been described as being associated with STEC infections in humans or isolated from animals. Thirty-four strains (61%) within seven serotypes (O103:H2 [14 isolates], O26:H11 [6 isolates], O145:H28 [4 isolates], O145:HNM [3 isolates], O15:HNM [3 isolates], OX174:H21 [2 isolates], and O Rough:HNM [2 isolates]) were represented by more than one isolate. Of these strains, O103:H2 isolates were divided into seven, O26:H11 isolates were divided into four, and the rest within a serotype were divided into two genotypes in PFGE. In PCR, 31 (55%) of the 56 strains were positive for the stx(2) gene only and 24 strains (43%) were positive for stx(1) only. One strain (O43:H2) carried both stx(1) and stx(2). Forty-two strains (75%) produced enterohemolysin, and 39 strains (70%) possessed the eae gene. Of the latter 39 strains, 36 (92%) were enterohemolytic, whereas only 6 (35%) of the 17 isolates lacking the eae gene were enterohemolytic (P < 0.001). The majority of the strains (44 strains, 79%) were sensitive to all 12 antimicrobials tested. Of the 56 strains, 20 (36%) were associated with small family outbreaks in nine families and 14 (25%) were associated with recent travel abroad.