Genes coding for Shiga-like toxins in bovine verotoxin-producing Escherichia coli (VTEC) strains belonging to different O:K:H serotypes

Antimicrobial Resistance, Serologic and Molecular Characterization of E. coli Isolated from Calves with Severe or Fatal Enteritis in Bavaria, Germany

Worldwide, enterotoxigenic Escherichia coli (ETEC) cause neonatal diarrhea and high mortality rates in newborn calves, leading to great economic losses. In Bavaria, Germany, no recent facts are available regarding the prevalence of virulence factors or antimicrobial resistance of ETEC in calves. Antimicrobial susceptibility of 8713 E. coli isolates obtained from 7358 samples of diseased or deceased diarrheic calves were investigated between 2015 to 2019. Considerably high rates of 84.2% multidrug-resistant and 15.8% extensively drug-resistant isolates were detected. The resistance situation of the first, second and third line antimicrobials for the treatment, here amoxicillin-clavulanate, enrofloxacin and trimethoprim-sulfamethoxazole, is currently acceptable with mean non-susceptibility rates of 28.1%, 37.9% and 50.0% over the investigated 5-year period. Furthermore, the ETEC serotypes O101:K28, O9:K35, O101:K30, O101:K32, O78:K80, O139:K82, O8:K87, O141:K85 and O147:K89, as well as the virulence factors F17, F41, F5, ST-I and stx1 were identified in a subset of samples collected in 2019 and 2020. The substantially high rates of multi- and extensively drug-resistant isolates underline the necessity of continuous monitoring regarding antimicrobial resistance to provide reliable prognoses and adjust recommendations for the treatment of bacterial infections in animals.

Norwegian sheep are an important reservoir for human-pathogenic Escherichia coli O26:H11

A previous national survey of Escherichia coli in Norwegian sheep detected eae-positive (eae(+)) E. coli O26:H11 isolates in 16.3% (80/491) of the flocks. The purpose of the present study was to evaluate the human-pathogenic potential of these ovine isolates by comparing them with E. coli O26 isolates from humans infected in Norway. All human E. coli O26 isolates studied carried the eae gene and shared flagellar type H11. Two-thirds of the sheep flocks and 95.1% of the patients harbored isolates containing arcA allele type 2 and espK and were classified as enterohemorrhagic E. coli (EHEC) (stx positive) or EHEC-like (stx negative). These isolates were further divided into group A (EspK2 positive), associated with stx(2-EDL933) and stcE(O103), and group B (EspK1 positive), associated with stx(1a). Although the stx genes were more frequently present in isolates from patients (46.3%) than in those from sheep flocks (5%), more than half of the ovine isolates in the EHEC/EHEC-like group had multiple-locus variable number of tandem repeat analysis (MLVA) profiles that were identical to those seen in stx-positive human O26:H11 isolates. This indicates that EHEC-like ovine isolates may be able to acquire stx-carrying bacteriophages and thereby have the possibility to cause serious illness in humans. The remaining one-third of the sheep flocks and two of the patients had isolates fulfilling the criteria for atypical enteropathogenic E. coli (aEPEC): arcA allele type 1 and espK negative (group C). The majority of these ovine isolates showed MLVA profiles not previously seen in E. coli O26:H11 isolates from humans. However, according to their virulence gene profile, the aEPEC ovine isolates should be considered potentially pathogenic for humans. In conclusion, sheep are an important reservoir of human-pathogenic E. coli O26:H11 isolates in Norway.

Detection of Shiga toxin-producing Escherichia coli by PCR in cattle in Argentina. Evaluation of two procedures

Different experimental approaches were evaluated for their ability to detect stx genes by PCR and identify Shiga toxin-producing Escherichia coli (STEC) in bovine fecal samples. One hundred and sixty fecal samples from steers in Argentina were processed by protocols that involved: (1) enrichment of fecal samples and DNA extraction using a commercially available kit (Protocol A); (2) plating on selective media after enrichment of the fecal sample followed by heat-lysis DNA extraction from the confluent growth zone (Protocol B); (3) analysis of individual colonies isolated from direct fecal culture on MacConkey agar and sorbitol MacConkey agar supplemented with cefixime and potassium tellurite (Protocol C), used as Gold Standard. PCR performed on bacteria from the confluent growth zone (Protocol B) proved to be the most sensitive methodology. In addition, enrichment for greater than 6h, enhanced sensitivity. Among eight STEC isolates, four were O8:H19 and four were stx2/eae-negative. An STEC isolate was characterized as O26:H11 with a stx1/eae/EHEC-hlyA genotype, often associated with human disease. Finally, no STEC O157 strains were isolated using these methods.

Murine monoclonal antibodies against Escherichia coli O4 lipopolysaccharide and H5 flagellin

Two murine monoclonal antibodies (MAb), 2C5-F10 and 8D1-H10, reactive with Escherichia coli O4 and H5 antigens, respectively, were generated and characterized. Enzyme immunoassays and immunoblots demonstrated that MAb 2C5-F10 reacted specifically with lipopolysaccharide O antigen of E. coli O4 isolates, while MAb 8D1-H10 reacted with E. coli strains expressing H5 flagella.

Pathogenic characteristics of Escherichia coli strains isolated from newborn piglets with diarrhea in Brazil

Ninety-one Escherichia coli isolates obtained from diarrheic and normal feces of newborn piglets (0-11 days of age) from three states of Brazil were assessed for phenotypic and genotypic characteristics associated with pathogenic processes. These isolates expressed fimbriae F18ac and type 1, but not fimbriae K88, K99, 987P or F41. Genes for toxins (LT-I, STa, SLT-I, SLT-II, SLT-IIv) either individually or combined were found to be present in most of the diarrheic strains (65.7%) and in 42.8% of the non-diarrheic ones. The eaeA gene was present in 25.7% of the diarrheic isolates and in 9.5% of the non-diarrheic ones. Colicin, hemolysin and aerobactin were also found to be produced by some strains from both sources. Because of the great variety of biological characteristics associated with different illness processes, we suggest that, in Brazil, pigs may act as a reservoir for transmission of Escherichia coli strains to other animals.

Molecular characteristics and epidemiological significance of Shiga toxin-producing Escherichia coli O26 strains

Fifty-five Shiga toxin (Stx)-producing Escherichia coli (STEC) O26:H11 and O26:H(-) strains isolated from humans between 1965 and 1999 in Germany and the Czech Republic were investigated for their chromosomal and plasmid characteristics. All motile (n = 23) and nonmotile (n = 32) STEC O26 strains were shown to possess the identical flagellin subunit-encoding gene (fliC). We observed a striking recent shift of the stx genotype from stx(1) to stx(2) among the STEC O26 isolates. While stx(1) was the exclusive genotype identified in our collection until 1994, 94% of the isolates obtained after 1997 possessed stx(2) either alone (71%) or together with stx(1) (23%). Plasmid profiling demonstrated a remarkable heterogeneity with respect to plasmid sizes and combinations. Southern blot analysis of plasmid DNA with probes specific to potential accessory virulence genes revealed considerable additional variability in gene composition and arrangement. Pulsed-field gel electrophoresis (PFGE) differentiated 16 subgroups among the 55 STEC O26 strains. Using these techniques we demonstrate the emergence of a new clonal subgroup characterized by PFGE pattern A and a unique combination of virulence markers including stx(2) and a single, approximately 90-kb plasmid harboring the enterhemorrhagic E. coli hlyA and etp genes. The proportion of PFGE subgroup A strains among STEC O26 isolates rose from 30% in 1996 to more than 50% in 1999. Four clusters of infections with the clonal subgroup A were identified. We conclude that the STEC serogroup O26 is diverse and that pathogenic clonal subgroups can rapidly emerge during short intervals. The extensive genetic diversity of STEC O26 provides a basis for molecular subtyping of this important non-O157 STEC serogroup.

Characterization of eae+ Escherichia coli isolated from healthy and diarrheic calves

Strains of Escherichia coli from 101 healthy and 114 diarrheic calves were screened by PCR for the eae (intimin) gene and Shiga toxin genes (stx). Each eae+ and eae/stx+ strain was examined for antimicrobial susceptibility, enterohemolysin activity, and the somatic O antigen was determined. An immunoassay was used to detect Shiga toxin antigens for the eae/stx+ E. coli. Significantly more (p = 0.005) of the healthy calves carried eae+ and eae/stx+ E. coli in their feces when compared to strains from diarrheic calves. Moreover, Shiga toxin antigens were detected significantly more (p = 0.001) often among the eae/stx+ strains from healthy calves when compared to eae/stx+ strains from diarrheic calves. However, significantly more (p = 0.001) of the eae+ and eae/stx+ strains from diarrheic calves were resistant to at least one of the antimicrobials tested, and the strains from diarrheic calves had a significantly (p = 0.05) higher rate of antimicrobial resistance to at least two different antimicrobial classes. No significant difference (p> or =0.05) was detected among the eae+ and eae/stx+ strains from healthy and diarrheic calves for enterohemolysin production. Serogroups O-negative, O5, O26, and O111 were predominate among both healthy and diarrheic calves.

Virulence properties of Shiga toxin-producing Escherichia coli (STEC) strains of serogroup O118, a major group of STEC pathogens in calves

Shiga toxin-producing Escherichia coli (STEC) strains of serogroup 0118 are the most prevalent group among STEC strains in diarrheic calves in Germany (L. H. Wieler, Ph.D. thesis, University of Giessen, 1997). To define their virulence properties, 42 0118 (0118:H16 [n = 38] and 0118:H- [n = 4]) strains were characterized. The strains displayed three different Stx combinations (Stx1 [36 of 42], Stx1 and Stx2 [2 of 42], and Stx2 [4 of 42]). A total of 41 strains (97.6%) harbored a large virulence-associated plasmid containing hlyEHEC (hly from enterohemorrhagic E. coli). The strains' adhesive properties varied in relation to the eukaryotic cells tested. Only 28 of 42 strains (66.7%) showed localized adhesion (LA) in the human HEp-2 cell line. In contrast, in bovine fetal calf lung (FCL) cells, the number of LA-positive strains was much higher (37 of 42 [88.1%]). The locus of enterocyte effacement (LEE) was detected in 41 strains (97.6%). However, not all LEE-positive strains reacted positively in the fluorescence actin-staining (FAS) test, which indicated the attaching and effacing (AE) lesion. In HEp-2 cells, only 22 strains (52.4%) were FAS positive, while in FCL cells, the number of FAS-positive strains was significantly higher (38 of 42 [90.5%; P < 0.001]). In conclusion, the vast majority of the 0118 STEC strains from calves (41 of 42 [97.6%]) have a high virulence potential (stx, hlyEHEC, and LEE). This virulence potential and the high prevalence of STEC 0118 strains in calves suggest that these strains could be a major health threat for humans in the future. In addition, the poor association between results of the geno- and phenotypical tests to screen for the AE ability of STEC strains calls the diagnostic value of the FAS test into question.

Cytotoxin produced by Escherichia coli isolated from chickens with swollen head syndrome (SHS)

This study was conducted to determine the presence of selected virulence factors in Escherichia coli recovered from swollen head syndrome (SHS) in chickens. Thirty-six (72%) of 50 isolates of E. coli from SHS were shown to produce a cytotoxin that was active on Vero and HeLa but not on Y-1 cells. The toxin was called VT2y because the cytotoxic effect on Vero cells was morphologically similar to that produced by E. coli verotoxins (VTs), and this effect was neutralized by antiserum against VT2 but not by antiserum against VT1. Interestingly, DNA probes for VT1 and VT2 failed to hybridize the VT2y-positive isolates with total DNA. Although the role of this toxin in SHS has yet to be demonstrated, the marked edema which characterizes affected chickens is consistent with the action of a toxin such as verotoxin which targets vascular endothelium.

PCR-based detection of verotoxin-producing Escherichia coli (VTEC) in ground beef

Pathogenic strains of Escherichia coli producing verotoxins (VTs) have been recognized as a cause of human disease, and rapid and sensitive detection tests are urgently needed to ensure the safety of food, especially ground beef. We applied two nested polymerase chain reaction (PCR) assays to detect the genes encoding VT1 and VT2 irrespective of the bacterial serotype. In combination with a direct sample preparation protocol, we were able to uncover the presence of about 110 CFU of verotoxinogenic E. coli (VTEC) in 10 g of ground beef. When a six-hour enrichment was included, we found the detection limit to be in the range of 1 to 10 bacterial cells per 10 g of ground beef. To evaluate our detection system, we tested 30 ground beef samples originating from butcher shops in Berne, Switzerland. One sample yielded positive PCR results for both the VT1 and VT2 genes, indicating the presence of verotoxinogenic E. coli. Finally, 20 food homogenates, shown to contain E. coli strains by standard culture, were analysed with our method, and the gene encoding VT2 was detected in one cheese sample. The results suggest that the described PCR method can serve as a valuable tool for the surveillance of VTEC contamination of foods.

Genes coding for enterotoxins and verotoxins in porcine Escherichia coli strains belonging to different O:K:H serotypes: relationship with toxic phenotypes

Seventy-four E. coli strains isolated from piglets with diarrhea or edema disease in Spain were serotyped and examined for production of heat-labile (LT) and heat-stable (ST) enterotoxins (LT-I, LT-II, STaH, STaP, and STb) and verotoxins (VT1, VT2, and VT2v = VTe) by phenotypic (Vero cell assay and infant mouse test) and genotypic (colony hybridization and PCR) methods. In general, an excellent correlation was found between the results obtained with a PCR approach and those determined with biological assays. DNA probes used in the hybridization also showed a very good agreement with phenotypic results, with the exception of a VT1 probe that initially produced 10 false-positive reactions. The gene coding for STb (58 strains) was the most prevalent gene detected by PCR, followed by those coding for STa (46 strains), LT (19 strains), VT2v (11 strains), and VT1 (1 strain). Apparently, in Spain three seropathotypes are predominant: (i) O149:K91:H10 K88+ LT-I+ STb+, (ii) O141:K85ab:H- P987+ STaP+, and (iii) O138:K81:H14 or H- STaP+ VT2v+. We conclude that PCR is a fast, specific, and practical method for the identification of enterotoxin and VT genes in clinical and epidemiological studies.

Production of toxins (enterotoxins, verotoxins, and necrotoxins) and colicins by Escherichia coli strains isolated from septicemic and healthy chickens: relationship with in vivo pathogenicity

Since the mechanism of virulence of Escherichia coli strains pathogenic to birds is not fully understood, the prevalence of toxic factors produced by E. coli strains pathogenic to other animals was investigated. A total of 625 E. coli strains isolated from visceral organs of chickens with colisepticemia and from feces of healthy chickens in Spain were tested for production of enterotoxins (heat labile [LT] and heat stable [STa]), verotoxins (VT1, VT2, and VT2v), cytotoxic necrotizing factors (CNF1 and CNF2), alpha-hemolysin (Hly), enterohemolysin (EntHly), colicin V (Col V) and other types of colicins, and necrotic and lethal activities. Only 45 (7%) of avian E. coli strains were toxigenic: 20 strains produced a cytotoxic response in HeLa but not in Vero cells, indicating the production of a cytotoxin not related to the VTs; 16 were EntHly+; 5 produced a new cytotonic product that causes the appearance of whitish vacuola in Vero and HeLa cells; 3 synthesized soluble factors that cause lethal activity in mice; and 1 elaborated LT. None of 625 avian E. coli strains was positive for production of VTs or CNFs. In contrast, colicinogenicity occurred in 335 (73%) of the 458 septicemic strains and 97 (58%) of 167 fecal isolates (P < 0.01), and this property was correlated with in vivo pathogenicity of strains. Thus, 80% (P < 0.001) and 66% (P < 0.001) of strains producing Col V and other types of colicins were characterized as being of high pathogenicity, whereas only 15% of the noncolicinogenic strains were classified as highly pathogenic. Our results clearly support the special pathogenicity theory, because 60% of the E. coli strains belonging to 18 serogroups (O1, O2, O5, O8, O12, O14, O15, O18, O20, O53, O78, O81, O83, O102, O103, O115, O116, and O132) most frequently identified among clinical septicemic strains were classified as highly pathogenic in in vivo assays, whereas only 24% of the strains with O serogroups less prevalent among diseased chickens were considered highly pathogenic (P < 0.01).

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.

Distribution and characterization of faecal verotoxin-producing Escherichia coli (VTEC) isolated from healthy cattle

Faecal swabs obtained from a random sample of 268 cows and 90 calves on 19 Lugo farms were examined for verotoxin-producing Escherichia coli (VTEC). We found VTEC on 95% of the farms. The prevalence rates of VTEC infection in asymptomatic cows and calves were estimated to be 35 and 37%, respectively. The proportion of animals infected on each farm ranged from 0 to 100%. VTEC strains isolated from healthy cattle belonged to 27 O serogroups; however, 57% (85 of 149) were of one of 8 serogroups (O2, O8, O22, O77, O82, O105, O113 and O171). Nearly 60% of the bovine VTEC strains belonged to serogroups that cause haemorrhagic colitis and haemolytic uraemic syndrome in humans. The VTEC were all non-O157:H7; 91% were eae-negative and 86% produced VT2 or VT1 and VT2. These characteristics are different from those of VTEC isolated from calves with diarrhoea.

Virulence properties of Escherichia coli strains belonging to enteropathogenic (EPEC) serogroups isolated from calves with diarrhea

Nineteen Escherichia coli strains belonging to enteropathogenic (EPEC) serogroups were isolated from calves with diarrhea in Paraná State. Brazil, and studied for virulence markers associated with EPEC or enterohemorrhagic E. coli (EHEC). The 19 isolates belonged to 12 serotypes with isolates of O26:H11, O119:H25 and O114:H- being the most prevalent Localized adherence (LA) was demonstrated for 37% of the isolates, consisting of all four O26:H11, both O114:H- and one O114:H40 isolates. All the LA strains were positive in the fluorescent-actin staining (FAS) test and possessed attaching-effacing E. coli (eae) sequences, but only O114 strains hybridized with the EPEC adherence factor (EAF) probe. None of the strains produced Shiga-like toxins (Verotoxin). Only the O26:H11 strains hybridized with the EHEC plasmid specific (CVD419) probe and were enterohemolytic, properties associated with EHEC strains. This investigation demonstrates that among the bovine strains isolated only those of serogroup O114 behaved as typical EPEC.

Shiga toxin-producing Escherichia coli strains from bovines: association of adhesion with carriage of eae and other genes

Out of 174 bovine Shiga toxin-producing Escherichia coli (STEC) strains isolated from diarrheic calves in Germany and Belgium, 122 strains (70.1%) were selected because of their reactivity with the eae (E. coli attaching and effacing gene) probe ECW1-ECW2. One hundred seven of these eae-positive strains (87.7%) harbored stx1 genes, 13 strains (10.7%) had stx2 genes, and 2 strains (1.6%) had both stx genes. The strains displayed 17 different O types, the majority (97 strains) [79.5%]) belonging to O5 (5 strains), O26 (21 strains), O111 (13 strains) O118 (36 strains), O145 (9 strains), and O157 (13 strains). In the HEp-2 cell adhesion assay, 99 strains (81.1%) showed a localized adhesion, and 80 strains (65.6%) stimulated actin accumulation, as determined in the fluorescence actin staining test. None of the strains harbored genes coding for bundle-forming pili (bfpA), clearly differentiating them from enteropathogenic. E. cole. espB gene sequences were only detectable in 23 (18.9%) of the eae-positive bovine STEC strains. Three different PCRs were established, differentiating between eae sequences of enteropathogenic E. coli strain E2348/69 (O127:H6) and STEC strain EDL933 (O157: H7). Primers matching in the more heterologous downstream eae sequences gave amplicons in only 8 of the 17 O types (O84:H-, O103:H2, O111:H-, O111:H2, O119:H25, O128:H-, O145:H28, and O157:H-). Only 15 STEC strains, belonging to serotypes O111H:-, O111H:2, O145:H28, and O157:H-, gave amplicons in all three eae-specific PCRs. These data demonstrate that bovine STEC strains are a heterogeneous group of pathogenic bacteria, a lot of which share virulence markers with STEC strains causing infections in humans. However, in contrast to human STEC strains, bovine eae-positive STEC strains are mainly restricted to the stx1 genotype. The observation that espB sequences are not highly conserved might have consequences for the serological recognition of the ESPB protein in patients. Like in human STEC strains, eae-related sequences are closely associated with certain E. coli O groups; however, they are not serotype specific.

O serogroups, biotypes, and eae genes in Escherichia coli strains isolated from diarrheic and healthy rabbits

A total of 305 Escherichia coli strains isolated from diarrheic and healthy rabbits in 10 industrial fattening farms from different areas of Spain were serotyped, biotyped, and tested for the presence of the eae gene and toxin production. The characteristics found in strains isolated from healthy rabbits were generally different from those observed in E. coli strains associated with disease. Thus, strains with the eae gene (74% versus 22%); strains belonging to serogroups O26, O49, O92, O103, and O128 (64% versus 12%); rhamnose-negative strains (51% versus 5%); and rhamnose-negative O103 strains with eae genes present (41% versus 1%) were significantly (P < 0.001 in all cases) more frequently detected in isolates from diarrheic animals than in those from healthy rabbits. Whereas a total of 35 serogroups and 17 biotypes were distinguished, the majority of the strains obtained from diarrheic rabbits belonged to only four serobiotypes, which in order of frequency were O103:B14 (72 strains), O103:B6 (16 strains), O26:B13 (12 strains), and O128:B30 (12 strains). These four serobiotypes accounted for 48% (112 of 231) and 5% (4 of 74) of the E. coli strains isolated from diarrheic and healthy rabbits, respectively. Only six strains were toxigenic (three CNF1+, two CNF2+, and one VT1+). We conclude that enteropathogenic E. coli strains that possess the eae gene are a common cause of diarrhea in Spanish rabbit farms and that the rhamnose-negative highly pathogenic strains of serotype O103:K-:H2 and biotype B14 are especially predominant. Detection of the eae gene is a useful method for the identification of enteropathogenic E. coli strains from rabbits. However, a combination of serogrouping and biotyping may be sufficient to accurately identify the highly pathogenic strains for rabbits.

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.

Prevalence and characteristics of human and bovine verotoxigenic Escherichia coli strains isolated in Galicia (north-western Spain)

An epidemiological study was carried out to determine the incidence and the serotypes of verotoxigenic Escherichia coli (VTEC) that cause infections in Galicia (north-western Spain). Although, VTEC strains were isolated from 55 (14%) of the 387 calves sampled and the majority of bovine VTEC strains belonged to serotypes (026:H11 or H-, 091:H21, O103:H2, 0105:H18, O111:H-O113:H21, O126:H-, O128:H- and O157:H7 or H-) previously associated with human haemorrhagic colitis (HC) and haemolytic uraemic syndrome (HUS) in other countries, VTEC are not a common cause of human infections in Spain. Thus, VTEC (O26:H11 and O86:H10) were isolated from only 3 (0.6%) of the 482 children with diarrhoea investigated. We examined the 69 (3 humans and 66 bovines) VTEC strains that were initially isolated as E. coli producing a toxin cytotoxic to Vero and HeLa cells by polymerase chain reaction (PCR) using specific primers for VT1, VT2 and eae genes. PCR showed that 38 (55%) of VTEC strains carried VT1 genes. 18 (26%) possessed VT2 genes, and 10 (14%) carried both VT1 and VT2 genes. Three (one human and two bovine) strains which were formerly VTEC had lost the ability to produce verotoxins upon subculture and became negative for VT1 and VT2 by PCR. In total 35 (51%) of 69 VTEC strains, including the two human VT1+ strains of serotype O26:H11, were positive for eae sequences when tested by PCR. Presence of the eae gene was significantly more frequent (100%; 21/21) among VTEC strains with serotypes (O26:H11, O111:H-, O157:H-and O157:H7) considered as enterohaemorrhagic E. coli (EHEC) than among VTEC strains with non-EHEC serotypes (29%; 14/48) (p < 0.001). Results obtained in this study indicate that cattle may be an important source of VTEC involved in human disease. However, severe clinical syndromes caused by VTEC, such as HC and HUS, are uncommon in Spain, in comparison with North America and the UK. In any case, VTEC disease can appear on the scene very suddenly, as occurred in the UK and North America in the 1980s.