Escherichia coli O157:H7 diarrhoea associated with well water and infected cattle on an Ontario farm

A 16-month old female child living on an Ontario dairy farm was taken to hospital suffering from bloody diarrhoea. Escherichia coli O157:H7 was isolated from her stool. Initial tests of well water samples were negative for E. coli by standard methods but culture of selected coliform colonies on sorbitol-MacConkey agar led to isolation of E. coli O157:H7. E. coli O157:H7 was also isolated from 63% of cattle on the farm. The E. coli O157:H7 isolates from the child, the water and the cattle were phage type 14, produced verotoxins 1 and 2, and were highly related on analysis by pulsed field gel electrophoresis. The child did not have known direct contact with the cattle and did not consume unpasteurized milk. Hydrogeological investigation revealed the design and location of the well would allow manure-contaminated surface water to flow into the well. This investigation demonstrates that cattle farm well water is a potential source of E. coli O157:H7 which may not be identified by standard screening for E. coli in water.

Rapid pulsed-field gel electrophoresis protocol for typing of Escherichia coli O157:H7 and other gram-negative organisms in 1 day

Genomic DNA patterns generated by pulsed-field gel electrophoresis are highly specific for different strains of an organism and have significant value in epidemiologic investigations of infectious-disease outbreaks. Unfortunately, time-consuming and tedious specimen processing is an inherent problem which limits the use of this powerful technology as a real-time epidemic investigational tool. Here, I describe a rapid method to improve the response time and provide specific bacterial strain identification for the typing of Escherichia coli O157:H7 and other gram-negative organisms in a single day.

Escherichia coli associated cellulitis in broilers: correlation with systemic infection and microscopic visceral lesions, and evaluation for skin trimming

In Alberta, cellulitis condemnations average 0.5% and are among the highest in Canada. Presently, all cellulitis-affected birds are condemned for fear of systemic infections and public health implications. In a slaughterhouse sample of 102 birds condemned with cellulitis, Escherichia coli was isolated from 83.3% of the lesions. All hearts were cultured and from 11.2% E. coli was recovered. Gross lesions of perihepatitis, infected oviducts, and arthritis were found in 11.2%, 6.7%, and 2.9% of the birds, respectively. Serotyping suggested that visceral infection occurs independent of cellulitis in at least half of the cases. There was no correlation between microscopic visceral lesions and positive bacterial cultures. Two E. coli isolates of serogroup 0157 produced no toxin and neither isolate produced CS31A, F107, or F1845 fimbriae. Cellulitis lesions ranged from 0.55 to 218.9 cm2. All lesions under 16 cm2 and 64% of lesions up to 48 cm2 were considered suitable for trimming.

Detection of STEC and epidemiological investigations in surrounding of a HUS patient

After occurrence of a case of HUS infection in a 2-year-old infant from a dairy farmer's family living near Oldenburg, investigations were performed in the infant's surrounding in order to elucidate the route of infection. Since hospitalization took place at a late stage, it was not possible to isolate EHEC from the patient's stool samples. However, E. coli O157 antibody determinations in serum were positive. Since STEC of serogroup O157 were found in faeces from the 34 dairy cows of the farm, stool samples were taken from 6 members of the child's family and examined. Non-O157 STEC could be isolated from the stools of 2 family members. Determination of other virulence factors and other characteristics such as serotype, biotype and phage type showed identity of the agent for 3 isolates (2 from animals, 1 from humans). By means of pulsed-field gel electrophoresis of the restricted DNA of the isolates and by means of RAPD-PCR it was not possible to establish any differences in the band patterns. It can be assumed, therefore, that the organisms had been transmitted from animals to humans.

[A study for serodiagnosis of verotoxin-producing Escherichia coli (enterohemorrhagic E. coli) O157 by the bacterial agglutination technique]

We evaluated the usefulness of bacterial agglutination antibodies for serodiagnosis of verotoxin-producing Escherichia coli (enterohemorrhagic E. coli) O157 infections. We examined 50 serum samples from 50 control children (whiout diarrhea 31, with diarrhea 19), 24 samples from 8 diarrhea cases due to O157:H7, 37 samples from 14 cases of hemolytic uremic syndrome (HUS) for antibodies to heat-killed E. coli E32511 (O157:H.-) strain using the bacterial agglutination technique. Of the control sera all but one (x80) showed 20 > or = in the antibody. All the diarrhea patients due to O157:H7 showed a significant rise (x160-x5120) of the titers in the sera at 5-7 days on illness, after that the titers fell rapidly. Significant antibody rise (x160-x5120) was detected in twelve out of 14 HUS patients at the early stage of the illness which fell in the convalescent phase. The assay appeared to be a useful serodiagnostic technique because of its easiness and simplicity as well as because of its high sensitivity and specificity.

A prolonged outbreak of Escherichia coli O157:H7 infections caused by commercially distributed raw milk

A protracted outbreak of Escherichia coli O157:H7 infections was caused by consumption of unpasteurized ("raw") milk sold at Oregon grocery stores. Although it never caused a noticeable increase in reported infections, the outbreak was recognized because of routine follow-up interviews. Six of 16 Portland-area cases reported between December 1992 and April 1993 involved people who drank raw milk from dairy A. By pulsed-field gel electrophoresis (PFGE), E. coli O157:H7 isolates from these cases and from the dairy A herd were homologous (initially, 4 of 132 animals were E. coli O157:H7-positive). Despite public warnings, new labeling requirements, and increased monitoring of dairy A, retail sales and dairy-associated infections continued until June 1994 (a total of 14 primary cases). Seven distinguishable PFGE patterns in 3 homology groups were identified among patient and dairy herd E. coli O157:H7 isolates. Without restrictions on distribution, E. coli O157:H7 outbreaks caused by raw milk consumption can continue indefinitely, with infections occurring intermittently and unpredictably.

Surveillance for Escherichia coli O157:H7 infections in Minnesota by molecular subtyping

BACKGROUND

Escherichia coli O157:H7 is a leading cause of diarrhea and the hemolytic-uremic syndrome. Current public health surveillance for E. coli O157:H7 requires considerable resources; traditional methods lack the sensitivity and specificity to detect outbreaks effectively.

METHODS

During 1994 and 1995, the Minnesota Department of Health requested that all clinical isolates of E. coli O157:H7 be submitted to our laboratory. Isolates were subtyped by pulsed-field gel electrophoresis (PFGE), and patients were interviewed about potential sources of infection.

RESULTS

In 1994 and 1995, 344 cases of E. coli O157:H7 infection were reported to the Minnesota Department of Health; 317 (92 percent) were subtyped by PFGE, and 143 distinct PFGE patterns were identified. Ten outbreaks of E. coli O157:H7 were identified; these accounted for 56 (18 percent) of the 317 subtyped cases. Four outbreaks were detected solely as a result of subtype-specific surveillance. In 11 two-week periods, the number of reported cases of E. coli O157:H7 doubled from the previous two weeks. In eight of these instances, the patterns identified were dissimilar and there were no outbreaks. Two of the remaining three increases resulted from multiple simultaneous outbreaks.

CONCLUSIONS

Subtype-specific surveillance for E. coli O157:H7 can identify outbreaks that are not detected by traditional methods and can ascertain whether sudden increases in reported cases are due to sporadic isolated cases or to one or more outbreaks.

Atypical strains of verocytotoxin-producing Escherichia coli O157 in beef cattle at slaughter in Veneto region, Italy

Cattle arriving for slaughter at abattoirs in the Veneto region of N. Italy were examined for intestinal carriage of Escherichia coli O157. Rectal swabs were cultured in modified buffered peptone water and E. coli O157 was concentrated by an immunomagnetic separation technique; the magnetic beads were cultured onto cefixime tellurite sorbitol MacConkey agar. Sorbitol non-fermenting E. coli O157 was isolated from 15 (3.6%) of 419 feedlot cattle but not from 437 veal calves or 65 culled cows. All strains of E. coli O157 hybridized with DNA probes specific for the VT1 or VT2 genes, but two strains did not produce toxin detectable by Vero cell assay. Six different plasmid profiles were observed with all strains harbouring the large 93 kb plasmid characteristic of VTEC. Six strains produced urease but otherwise strains were biochemically typical of E. coli O157. One strain was resistant to streptomycin, tetracycline and sulphonamides but the remainder were sensitive to all antimicrobials tested. This is the first description of the isolation of verocytotoxin-producing E. coli O157 from cattle in Italy. As the contamination of bovine carcasses with E. coli O157 during slaughter and processing has been demonstrated, the risk of transmission of this organism from beef cattle to the human population in the Veneto region, through foods of bovine origin or by other routes, should not be overlooked.

Molecular typing of enterohemorrhagic Escherichia coli O157:H7 isolates in Japan by using pulsed-field gel electrophoresis

Pulsed-field gel electrophoresis (PFGE) was applied for molecular typing of 825 enterohemorrhagic Escherichia coli (EHEC) O157:H7 isolates, most of which were from 19 outbreaks and 608 sporadic cases in Japan, mainly in May to August 1996. By PFGE, the EHEC O157:H7 isolates were classified into six types (type I to V and ND [nondescript]) and UT untypeable isolates. Fifty isolates from seven outbreaks in May to June and 60 isolates from patients with sporadic cases of infection showed almost identical PFGE patterns which differed in only 1 of 22 DNA fragments. They were classified into type I. Ninety-nine isolates from 10 other outbreaks and 156 isolates from patients in the Kinki area with sporadic cases of infection obtained in the early summer of 1996 showed identical PFGE patterns, suggesting that they were derived from one huge outbreak. They were classified into type II. Type IV EHEC isolates, which had only the stx2 gene, caused another outbreak in a primary school in June. EHEC isolates of two other types, types III and V, were not related to the outbreak but were isolated in several parts of Japan. ND EHEC isolates included a variety of patterns which could not be classified into either of the types mentioned above. Twenty-five isolates could not be analyzed due to degradation of their genomic DNAs and were represented as UT. These results indicate that EHEC O157:H7 strains with various PFGE types have already spread to Japan and caused the multiple outbreaks and sporadic infections in Japan in the summer of 1996.

Detection and characterization of enterohaemorrhagic Escherichia coli in slaughtered cattle

Fecal samples from slaughtered cattle were studied for enterohaemorrhagic Escherichia coli (EHEC) by DNA hybridization with biotin-labelled DNA probes specific for the EHEC virulence plasmid, Shiga-like toxin I (SLT I), Shiga-like toxin II (SLT II) and eae gene. Among 136 animals analysed, 47 (34.5%) were found to carry EHEC. The cytotoxic genotypes observed for EHEC strains were: 60.4% SLT I, 12.5% SLT II and 10.4% SLT I + SLT II; 16.7% resulted SLT I and SLT II negative. A total of 14 out of 48EHEC strains (29.2%) hybridized with a fimbrial probe and 14 of 48 strains with an sas probe. An important number of strains (18 out of 48) belonged to serogroups O157, O26 and O111, serogroups also commonly isolated from haemolytic uremic syndrome cases in Chile. While EHEC isolates from the same animal were usually of the same serogroup, one animal was found to carry two EHEC strains of different serogroups. A total of 50% of EHEC strains were sorbitol negative, irrespective of the O serogroup or EHEC genotypic profile. Results obtained in this study strongly suggest that cattle in Chile are a reservoir of EHEC associated with disease in humans.

Characterization of Escherichia coli O157:H7 and other Shiga toxin-producing E. coli serotypes isolated from sheep

The isolation and characterization of Escherichia coli O157:H7 and non-O157 Shiga toxin-producing E. coli (STEC) strains from sheep are described. One flock was investigated for E. coli O157:H7 over a 16-month period that spanned two summer and two autumn seasons. Variation in the occurrence of E. coli O157:H7-positive sheep was observed, with animals being culture positive only in the summer months but not in the spring, autumn, or winter. E. coli O157:H7 isolates were distinguished by pulsed-field gel electrophoresis (PFGE) of chromosomal DNA and toxin gene restriction fragment length polymorphism (RFLP) analysis. Ten PFGE patterns and five RFLP patterns, identified among the isolates, showed that multiple E. coli O157:H7 strains were isolated from one flock, that a single animal simultaneously shed multiple E. coli O157:H7 strains, and that the strains shed by individuals changed over time. E. coli O157:H7 was isolated only by selective enrichment culture off 10 g of ovine feces. In contrast, strains of eight STEC serotypes other than O157:H7 were cultured from feces of sheep from a separate flock without enrichment. The predominant non-O157 STEC serotype found was O91:NM (NM indicates nonmotile), and others included O128:NM, O88:NM, O6:H49, and O5:NM. Irrespective of serotype, 98% of the ovine STEC isolates possessed various combinations of the virulence-associated genes for Shiga toxin(s) and the attaching-and-effacing lesion (stx1, stx2, and eae), suggesting their potential for human pathogenicity. The most common toxin-eae genotype was positive for stx1, stx2, and eae. A Vero cell cytotoxicity assay demonstrated that 90% of the representative STEC isolates tested expressed the toxin gene. The report demonstrates that sheep transiently shed a variety of STEC strains, including E. coli O157:H7, that have potential as human pathogens.

[Molecular analysis of enterohemorrhagic Escherichia coli O157:H7 isolates in Japan 1996 using pulsed-field gel electrophoresis]

Using pulsed-field gel electrophoresis(PFGE) with XbaI digestion, we analyzed 1,794 enterohemorrhagic Escherichia coli(EHEC) O157 isolates, which were derived from 16 outbreaks, sporadic cases, foods, beef fecal swabs, and environments in 1996 in Japan. They were classified into six types according to observed PFGE patterns. EHEC O157:H7 isolates from seven out of the 16 outbreaks showed very closely related patterns and those from other five outbreaks did the same pattern; in the former outbreaks, no common source could be identified, while in the latter outbreaks, radish sprout is thought to be the common cause of the infection. PFGE patterns of the remaining four outbreaks were not correlated to each other.

Use of the flagellar H7 gene as a target in multiplex PCR assays and improved specificity in identification of enterohemorrhagic Escherichia coli strains

PCR products of 1.8 kb were generated with DNAs from all Escherichia coli H7 strains tested by using oligonucleotide primers which flank the fliC gene. Three RsaI digestion profiles of these PCR products were evident on agarose gels; the first occurred with serotype O55:H7, O157:H7, or nonmotile (NM) strains, the second occurred with serotype O1:H7 and O18:H7 strains, and the third occurred with serotype O?:H7, O19:H7, O121:H7, O88:H7, and O156:H7 strains. Despite these differences, the nucleotide sequences of the E. coli E32511 (O157:NM) and U5-41 (O1:H7) fliC genes were 97% homologous. Two PCR primer pairs synthesized on the basis of the E32511 H7 fliC sequence amplified specific DNA fragments from all E. coli H7 strains, but did not amplify DNA fragments from the other bacterial strains. The H7-specific primers were used in combination with other primers which target the Verotoxin 1(VT1) and VT2 genes and the E. coli O157:H7 eaeA gene in multiplex PCR assays. In these assays, vt and eaeA PCR products were observed with DNAs from the majority of EHEC strains and vt, eaeA, and fliC PCR products were observed with DNAs from E. coli O157:H7 or NM strains. Only eaeA PCR products were present with DNA from enteropathogenic E. coli, and only vt PCR products occurred with VT-producing E. coli which are not EHEC. The multiplex PCR assays described allow for the specific identification of E. coli O157:H7 or NM and other EHEC strains.

Production and characterization of monoclonal antibodies specific for the lipopolysaccharide of Escherichia coli O157

Identification of the O157 antigen is an essential part of the detection of Escherichia coli O157:H7, which is recognized as a major etiologic agent of hemorrhagic colitis. However, polyclonal antibodies produced against E. coli O157:H7 lipopolysaccharide (LPS) may react with several other bacteria including Brucella abortus, Brucella melitensis, Yersinia enterocolitica O9, Escherichia hermannii, and Stenotrophomonas maltophilia. We produced eight monoclonal antibodies (MAbs) specific for the LPS of E. coli O157. Western blots (immunoblots) of both the phenol phase (smooth) and the aqueous phase (rough) of hot phenol-water-purified LPS indicated that three of the MAbs were specific for the O antigen and five were reactive with the LPS core. The eight MAbs could be further differentiated by their reactivities to Salmonella O30 LPS (group N), which is reported to be identical to the E. coli O157 antigen. All eight MAbs reacted strongly to all of the 64 strains of E. coli O157 tested, which included 47 isolates of O157:H7 and 17 other O157 strains. None of the eight MAbs cross-reacted with any of the 38 other E. coli serotypes tested, which consisted of 29 different O-antigen serotypes, or with 38 strains (22 genera) of non-E. coli gram-negative enteric bacteria.

[Bacteriological detection methods of enterohemorrhagic Escherichia coli]

A rapid identification of enterohemorrhagic Escherichia coli is critical to diagnose and treat its infection due to a possible development of hemorrhagic colitis, hemolytic uremic syndrome and cerebral symptom. For that, several bacteriological detection methods are developed and some of them have been used in clinical microbiology laboratories. In this article, classical bacteriological methods, immunological methods and PCR for identification of enterohemorrhagic E. coli are reviewed and advantages as well as disadvantages of various methods are discussed.

[Diversity of DNA sequences among enterohemorrhagic Escherichia coli O157:H7 detected by PCR-based DNA fingerprinting]

A random amplified polymorphic DNA(RAPD) fingerprinting method has been developed to differentiate Enterohemorrhagic Escherichia coli(EHEC) O157:H7 isolates. This method uses an oligonucleotide of arbitrarily chosen sequence to prime DNA synthesis from pairs of sites to which it is matched or practically matched and results in strain-specific arrays of DNA products. By the RAPD analysis using A07(5'-TGCCTCGCACCA-3'), EHEC strains tested in this study were found to be divided into 5 groups. The RAPD arrays among 5EHEC clinical isolates from a single outbreak were identical from each other, and different from other origin. The data indicate that the RAPD method is feasible for investigating the source of an outbreak associated with EHEC O157:H7 infection.

Risk factors for sporadic infection with Escherichia coli O157:H7

BACKGROUND

Little is known about risk factors for sporadic infection with Escherichia coli O157:H7. In response to a sharp increase in reported cases in New Jersey during July 1994, we conducted a case-control study to identify principal sources of infection and contributing practices.

METHODS

Standardized questionnaires were used to evaluate (1) potential exposures of case patients and matched controls and (2) knowledge, attitudes, and practices of food preparers in case and control households. Patient isolates were subtyped by pulsed-field gel electrophoresis.

RESULTS

Patients with E coli O157:H7 infection (N = 23; median age, 9 years; 55% female) were more likely than healthy controls to have eaten a hamburger in the week preceding illness (matched odds ratio, undefined; P < .001); 80% of the hamburgers eaten by ill persons were prepared at home. Food preparers in case households were less likely than those in control households to report washing their hands (odds ratio, 8.5; P < .005) and work surfaces (odds ratio, 10.5; P < .05) after handling raw ground beef. Pulsed-field gel electrophoresis yielded 17 unique subtypes among the 23 patient isolates, indicating multiple sources of infection.

CONCLUSIONS

Hamburgers prepared at home are an important source of sporadic E coli O157:H7 infections. We estimate that adequate hand washing by food preparers could have prevented 34% of E coli O157:H7 infections in the study population.

Vero cytotoxin-producing Escherichia coli O157 outbreaks in England and Wales, 1995: phenotypic methods and genotypic subtyping

Vero cytotoxin-producing Escherichia coli O157 belonging to four phage types (PTs) caused 11 outbreaks of infection in England and Wales in 1995. Outbreak strains of different PTs were distinguishable by DNA-based methods. Pulsed-field gel electrophoresis best discriminated among strains belonging to the same PT, distinguishing six of the seven PT2 outbreak strains and both PT49 outbreak strains.

Enterohaemorrhagic Escherichia coli

Enterohaemorrhagic Escherichia coli produces Verotoxins (Shiga-like toxins) and causes diarrhoea, haemorrhagic colitis and haemorrhagic uraemic syndrome. The mode of action of the Shiga toxin family has been well characterized in numerous studies which have demonstrated that the toxin has RNA N-glycosidase activity, which inhibits the binding of EF-1-dependent aminoacyl-tRNA to the 60S ribosomal subunit of eukaryotic cells, thus resulting in an inhibition of protein synthesis of the cells. In 1996, an unexpectedly large number of outbreaks of food poisoning due to E. coli O157:H7 occurred in Japan. In addition, many sporadic cases of E. coli O157:H7 were also reported and a total of about 8400 patients were recorded during that year. In most of these cases, the food vectors could not be identified. The possibility of developing a candidate vaccine is also discussed in this article.

Nucleic acid scanning-by-hybridization of enterohemorrhagic Escherichia coli isolates using oligodeoxynucleotide arrays

Nucleic acid scanning by hybridization (NASBH) is a non-electrophoretic typing strategy that uses gridded oligonucleotides to reproducibly characterize arbitrarily amplified nucleic acid sequences. Membrane-bound arrays of terminally-degenerate oligonucleotides were hybridized to DNA amplification fingerprinting (DAF) products from enterohemorrhagic Escherichia coli O157:H7 isolates. Numerical and cluster analysis of 64 isolates, selected by DAF to represent a single dominant amplification type identified 14 hybridization types. Results show that NASBH is a powerful alternative for the identification of closely related bacteria, can be used successfully in epidemiological studies, and holds potential in general nucleic acid diagnostics.

Characterization of nonmotile variants of Escherichia coli O157 and other serotypes by using an antiflagellin monoclonal antibody

An antiflagellin monoclonal antibody (15D8) was used to detect the presence of flagella in nonmotile variants of several pathogenic Escherichia coli serotypes. Of the 48 isolates examined, 15 reacted with monoclonal antibody 15D8 and were culturally confirmed to be motile. Of the 38 clinical strains designated O157:NM or O157:H-, 7 were antibody reactive and motile and agglutinated with anti-H7 sera.

Prevalence and characteristics of Escherichia coli serotype O157:H7 and other verotoxin-producing E. coli in healthy cattle

From February to July of 1994, 328 faecal samples from 32 herds were collected and verotoxin-producing Escherichia coli (VTEC) found on 84% of the farms. The proportion of animals infected varied from 0-63%. VTEC were recovered from 52 (20%) of 257 cows and from 16 (23%) of 71 calves. Although the VTEC belonged to 25 different serogroups, 7 (O8, O20, O22, O77, O113, O126 and O162) accounted for 46% of strains. Nearly 45% of the strains. Nearly 45% of the 83 bovine VTEC strains belonged to serogroups associated with haemorrhagic colitis and haemolytic uraemic syndrome in humans. However, only 2 (2%) of 83 VTEC strains isolated from cattle belonged to enterohaemorrhagic E. coli (EHEC) serotypes (O26:H11 and O157:H7), and only 8 (10%) were positive for the attaching and effacing E. coli (eae) gene sequence. Polymerase chain reaction (PCR) showed that 17 (20%) of VTEC strains carried VT1 genes, 43 (52%) possessed VT2 genes, and 23 (28%) carried both VT1 and VT2 genes. Characterization of VTEC isolates revelated a heterogeneous population in terms of serogroup and toxin type in the positive herds. This study confirms that healthy cattle are a reservoir of VTEC, but, the absence of eae genes in most bovine VTEC strains suggests that they may be less virulent for humans than eae-positive EHEC.

Detection of enterohaemorrhagic Escherichia coli O157:H7 in minced beef using immunomagnetic separation

Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 has been recently recognized as a human pathogen associated with haemorrhagic colitis and haemolytic uraemic syndrome. Most outbreaks of haemorrhagic colitis resulted from the consumption of undercooked minced beef or raw milk. Dairy cattle have been identified as a reservoir of EHEC O157: H7. In this study E. coli O157 specific antibody, coated on magnetic beads, was used to concentrate and release EHEC O157:H7 from meat samples. A survey of retail fresh minced beef and hamburger samples using this procedure revealed that 3 (5%) of 58 beef samples were positive for EHEC O157:H7. Two of the strains produced both VT1 and VT2 verotoxins, and one produced only VT2. Immunomagnetic separation is a sensitive and simple technique for the isolation of E. coli O157 from food, and could be useful for a further elucidation of the epidemiology of this organism. The relatively high prevalence of EHEC O157:H7 in beef samples may constitute a risk for public health. Thus, a suitable epidemiologic control and effective methods of prevention should be applied.

Rapid genotyping of Escherichia coli O157 isolates by random amplification of polymorphic DNA

Although several typing methods have been described for Shiga-like toxin-producing Escherichia coli O157, the methods are somewhat cumbersome. Using 22 isolates of Escherichia coli O157 and five other Escherichia coli isolates, two primers (M13 core sequence and 970-11) were found to give excellent differentiation between isolates using random amplified polymorphic DNA (RAPD). Using only the presence or absence of variable bands, a matrix of 20 variable characters was identified. From these characters, similarity coefficients were calculated and a phenogram constructed. All of the Escherichia coli O157 isolates were easily distinguished from the non-O157 Escherichia coli isolates. Using a 95% similarity cutoff, we found 13 RAPD types among the 22 Escherichia coli O157 isolates. Isolates thought to be identical by toxin and phage typing as well as by epidemiological association were distinguished, and others thought to be distinct by lack of epidemiological association were identical. RAPD using M13 and 970-11 primers is a potentially useful typing tool for Escherichia coli isolates of serotype O157 and possibly other Escherichia coli isolates.

Evaluation of ribotyping as epidemiologic tool for typing Escherichia coli serogroup O157 isolates

A total of 121 representative Escherichia coli O157:H7 and O157:NM (nonmotile) isolates were characterized by ribotype, phage type, verotoxin genotype, and genomic fingerprints generated by pulsed-field gel electrophoresis. Ribotyping was not able to discriminate between O157:H7 isolates, and phage typing and pulsed-field gel electrophoresis were the most valuable and discriminatory techniques.