Molecular microbiological investigation of an outbreak of hemolytic-uremic syndrome caused by dry fermented sausage contaminated with Shiga-like toxin-producing Escherichia coli

Sequencing of Escherichia coli O111 O-antigen gene cluster and identification of O111-specific genes

Shiga toxin (Stx)-producing Escherichia coli strains of serogroup O111 are the most frequently isolated non-O157 strains causing outbreaks of gastroenteritis with hemolytic-uremic syndrome. The O111 O-antigen gene cluster had been cloned and about half of it has been sequenced; we have now sequenced the remainder of the gene cluster, which is 12.5 kb in length and which comprises 11 genes. On the basis of sequence similarity, we have identified all the O-antigen genes expected, including five sugar biosynthetic pathway genes, three transferase genes, the O-unit flippase gene, and the O-antigen polymerase gene. By PCR testing with E. coli strains representing all 166 O-antigen forms, some randomly selected gram-negative bacteria, and Salmonella enterica serovar Adelaide, we showed that four O-antigen genes are highly specific to O111. This work provides the basis for a sensitive test for the rapid detection of E. coli O111. This is important both for decisions related to patient care, because early treatment may reduce the risk of life-threatening complications, and for the detection of sources of contamination.

Verotoxin-producing Escherichia coli (VTEC) and eae-positive non-VTEC in 1-30-days-old diarrhoeic dairy calves

Faecal samples from 221, 1-30-days-old, diarrhoeic dairy calves were screened for the presence of verotoxin-producing Escherichia coli (VTEC) and eae-positive non-VTEC. Calves were grouped according to their age (1-7, 8-14, 15-21 and 22-30 days) and analyses of prevalences were done by Mantel-Haenzsel chi 2-test for trend. VTEC and eae-positive non-VTEC were detected in 20 (9.0%) and 18 (8.1%) of the diarrhoeic calves, respectively. A significant age-associated increase in the prevalence of VTEC (p = 0.0001), but not in the prevalence of eae-positive non-VTEC (p = 0.381), was found. Significant differences in VTEC prevalence were found between the age-group 22-30 days and in all other age-groups. 43 (5.0%) of the 861 E. coli isolates from the 221 diarrhoeic calves were VTEC, and 30 (69.8%) of these strains produced VT1 only. More than one-half of the VTEC strains (55.8%) were positive for the eae gene and all these eae-positive VTEC strains produced VT1 only. A high percentage (76.7%) of VTEC strains belonged to E. coli serogroups (O4, O26, O39, O91, O113, O128 and O145) associated with haemorrhagic colitis and haemolytic uraemic syndrome in humans. 51 (5.9%) of the E. coli strains studied were eae-positive non-VTEC and the serogroups most prevalent among these strains were O4, O14, O26 and O123. Only four of the eae-positive strains were also espB-positive by hybridization with a probe from a human EPEC isolate and none of these strains produced VT.

Pathogenesis and diagnosis of Shiga toxin-producing Escherichia coli infections

Since their initial recognition 20 years ago, Shiga toxin-producing Escherichia coli (STEC) strains have emerged as an important cause of serious human gastrointestinal disease, which may result in life-threatening complications such as hemolytic-uremic syndrome. Food-borne outbreaks of STEC disease appear to be increasing and, when mass-produced and mass-distributed foods are concerned, can involve large numbers of people. Development of therapeutic and preventative strategies to combat STEC disease requires a thorough understanding of the mechanisms by which STEC organisms colonize the human intestinal tract and cause local and systemic pathological changes. While our knowledge remains incomplete, recent studies have improved our understanding of these processes, particularly the complex interaction between Shiga toxins and host cells, which is central to the pathogenesis of STEC disease. In addition, several putative accessory virulence factors have been identified and partly characterized. The capacity to limit the scale and severity of STEC disease is also dependent upon rapid and sensitive diagnostic procedures for analysis of human samples and suspect vehicles. The increased application of advanced molecular technologies in clinical laboratories has significantly improved our capacity to diagnose STEC infection early in the course of disease and to detect low levels of environmental contamination. This, in turn, has created a potential window of opportunity for future therapeutic intervention.

Prevalence of bovine verotoxin-producing Escherichia coli in Argentina

Faecal swabs obtained from 126 calves and 118 cows in Argentina were investigated for the presence of verotoxin-producing Escherichia coli (VTEC). VTEC strains were recovered from 10 (23%) of 43 calves with diarrhoea, from 24 (29%) of 83 healthy calves, from 40 (44%) of 91 healthy cows waiting at the slaughterhouse, and from 6 (22%) of 27 healthy grazing cattle. PCR showed that 21 (9%) of animals carried VT1+ strains, 49 (20%) VT2+ strains and 10 (4%) VT1+ VT2+ strains. VT1+ strains predominated among calves (16% versus 0.8%; p < 0.001). The presence of eae gene was significantly more frequent among VTEC strains isolated from calves (78%; 46/59) than from cows (2%; 1/65) (p < 0.001). Furthermore, eae gene was more prevalent in VT1+ strains (97%; 32/33) than in VT2+ strains (14%; 10/70) (p < 0.001) and in VT1+ VT2+ strains (24%; 5/21) (p < 0.001). Sorbitol negative high virulent strains serogroups O157 were not detected. This study indicates that cattle are a reservoir of VTEC strains, and that eae gene is associated with VT1+ strains that are predominating among young animals. Fortunately, only adult animals are taken to the slaughterhouse, among which VTEC strains negative for eae gene are predominating.

A PCR specific for Escherichia coli O157 based on the rfb locus encoding O157 lipopolysaccharide

A PCR was developed for the detection of Escherichia coli O157 based on the rfbE O-antigen synthesis genes. A 479-bp PCR product was amplified specifically from E. coli O157 in cell lysates containing 200 or 2 CFU following crude DNA extraction. The PCR detected < 1 CFU of E. coli O157 per ml in raw milk following enrichment.

Haemolytic-uraemic syndrome outbreak caused by Escherichia coli O111:H-: clinical outcomes

In South Australia in 1995, we treated 20 children with haemolytic-uraemic syndrome associated with Escherichia coli O111:H-. The source of the outbreak was contaminated locally produced semi-dry fermented sausage (mettwurst). One child died of multiple haemorrhagic cerebral infarcts. Eighteen children required renal dialysis (for a median of 14 days); 12 months after discharge five still had significant impairment of renal function. Other major complications included colonic necrosis (3), cerebral haemorrhage/infarction (3), convulsions (4), and glucose intolerance (2). Although E. coli O111:H- has been associated with sporadic cases of haemolytic-uraemic syndrome, this was the first large outbreak reported in Australia.

Non-O157:H7 Stx2-producing Escherichia coli strains associated with sporadic cases of hemolytic-uremic syndrome in adults

From August 1996 to May 1997, six verotoxin-producing Escherichia coli (VTEC) strains were isolated from stool specimens of adults suffering from hemolytic-uremic syndrome (HUS). All the isolates were stx2 positive and belonged to different serotypes: O6:H4, O91:H10, O91:H21, O rough:H16, OX3:H-, and O nontypeable: H-. The enterohemolysin (Ehly)-encoding genes were detected in two isolates, and none of the isolates harbors the intimin (Eae)-encoding gene. These findings suggest that stx2-positive non-O157:H7 VTEC is a major cause of HUS in adults and that several sources of pathogens are responsible for local endemic infections.

Influence of cold stress on the preliminary enrichment time needed for detection of enterohemorrhagic Escherichia coli in ground beef by PCR

The influence of cold stress at 4 and 0 degree C on the detection time as assessed by impedance technology (Bactometer; Biomérieux, Marcy l'Etoile, France) of different enterohemorrhagic Escherichia coli (EHEC) strains was determined. Although there is some variation in susceptibility among EHEC strains, prolonged exposure of EHEC to cold stress, i.e., 4 and 5 days at 4 and 0 degree C, respectively, in general significantly increased their detection time. This reflects an increase of the lag-phase time caused by cold stress. Two EHEC strains were selected to determine the minimum preliminary enrichment time that would ensure a positive PCR detection of low numbers of verotoxin-producing E. coli (VTEC; 2 to 2 x 10(5) CFU/25 g) inoculated into ground beef (25 g) and stored at 4 or -20 degrees C for 8 and 14 days, respectively. Incubation times of 6 and 9 h of 1 to 10 CFU/g and 1 to 10 CFU/25 g, respectively, were sufficient for PCR detection of VTEC in ground beef when analysis was performed immediately after inoculation (no cold stress). When cells are exposed to cold stress (4 or -20 degrees C) a 24-h enrichment period is recommended. Restriction of enrichment time to 9 h under these circumstances decreases the sensitivity of PCR detection to 80 CFU/g. Hence, to obtain maximum sensitivity, PCR detection of VTEC in naturally contaminated ground beef should be performed after 24 h of enrichment.

Molecular analysis of Shiga toxigenic Escherichia coli O111:H- proteins which react with sera from patients with hemolytic-uremic syndrome

Western blot analysis was used to assess the reactivity of convalescent-phase sera from patients who were associated with an outbreak of hemolytic-uremic syndrome (HUS) caused by fermented sausage contaminated with Shiga toxin-producing Escherichia coli (STEC). The predominant STEC isolated from HUS patients belonged to serotype O111:H-, and reactivity to O111:H- whole-cell lysates, treated or untreated with proteinase K, was examined. As expected, all five serum samples demonstrated a marked anti-lipopolysaccharide response, but several protein bands were also immunoreactive, particularly one with an apparent size of 94 kDa. One convalescent-phase serum sample was subsequently used to screen an O111:H- cosmid bank and 2 of 900 cosmid clones were found to be positive, both of which contained a similar DNA insert. Western blot analysis of one of these clones identified three major immunoreactive protein bands of approximately 94, 70, and 50 kDa. An immune response to the three proteins was detectable with all five convalescent-phase serum samples but not with healthy human serum. Immunoreactive 94- and 50-kDa species were produced by a deletion derivative of the cosmid containing a 7-kb STEC DNA insert. Sequence analysis of this region indicated that it is part of the locus for enterocyte effacement, including the eaeA gene which encodes intimin. The deduced amino acid sequence of the O111:H- intimin was 88.6% identical to intimin from O157:H7 STEC, and the most divergent region was the 200 residues at the carboxyl terminus, which were only 75% identical. Such variation may be antigenically significant as serum from a HUS patient infected only with the O111:H- STEC reacted with intimin from an enteropathogenic E. coli O111 strain, as well as several other eaeA-positive STEC isolates, but not with an eaeA-positive STEC belonging to serotype O157:H-. Sera from two of the other HUS patients also failed to react with intimin from this latter strain. However, intimin from O157:H- STEC did react with serum from a patient infected with both O111:H- and O157:H- STEC.

Enteroaggregative, Shiga toxin-producing Escherichia coli O111:H2 associated with an outbreak of hemolytic-uremic syndrome

Shiga toxin-producing Escherichia coli O111:H2 strains from an outbreak of hemolytic-uremic syndrome showed aggregative adhesion to HEp-2 cells and harbored large plasmids which hybridized with the enteroaggregative E. coli probe PCVD432. These strains present a novel combination of virulence factors and might be as pathogenic to humans as the classic enterohemorrhagic E. coli.

Detection and characterization of Shiga toxigenic Escherichia coli by using multiplex PCR assays for stx1, stx2, eaeA, enterohemorrhagic E. coli hlyA, rfbO111, and rfbO157

Shiga toxigenic Escherichia coli (STEC) comprises a diverse group of organisms capable of causing severe gastrointestinal disease in humans. Within the STEC family, certain strains appear to be of greater virulence for humans, for example, those belonging to serogroups O111 and O157 and those with particular combinations of other putative virulence traits. We have developed two multiplex PCR assays for the detection and genetic characterization of STEC in cultures of feces or foodstuffs. Assay 1 utilizes four PCR primer pairs and detects the presence of stx1, stx2 (including variants of stx2), eaeA, and enterohemorrhagic E. coli hlyA, generating amplification products of 180, 255, 384, and 534 bp, respectively. Assay 2 uses two primer pairs specific for portions of the rfb (O-antigen-encoding) regions of E. coli serotypes O157 and O111, generating PCR products of 259 and 406 bp, respectively. The two assays were validated by testing 52 previously characterized STEC strains and observing 100% agreement with previous results. Moreover, assay 2 did not give a false-positive O157 reaction with enteropathogenic E. coli strains belonging to clonally related serogroup O55. Assays 1 and 2 detected STEC of the appropriate genotype in primary fecal cultures from five patients with hemolytic-uremic syndrome and three with bloody diarrhea. Thirty-one other primary fecal cultures from patients without evidence of STEC infection were negative.

Antibodies to lipopolysaccharide block adherence of Shiga toxin-producing Escherichia coli to human intestinal epithelial (Henle 407) cells

Shiga toxin-producing Escherichia coli (STEC) are a diverse group of organisms known to cause diarrhoea, haemorrhagic colitis and haemolytic uraemic syndrome (HUS) in humans. During the early stage of infection, numbers of STEC in the gut may be very high (of the order of 10(9)/g faeces), but as disease progresses, the numbers may drop rapidly such that STEC are undetectable within a week. Convalescent sera from patients recovering from HUS frequently contain high levels of antibody to E. coli lipopolysaccharide (LPS) of the infecting serotype, and it is possible that a local immune response to LPS contributes to elimination of the organism from the gut. We have recently demonstrated that STEC strains isolated from HUS cases have enhanced adherence to a human intestinal epithelial cell line (Henle 407) compared with STEC strains from non-human sources. In this study, we examined the capacity of STEC strains belonging to O-antigen types O111 and O157 to adhere to human intestinal epithelial (Henle 407) cells in the presence or absence of anti-LPS. Adherence was inhibited by up to 95% by anti-LPS of the homologous, but not heterologous serotype. This effect was not an artefact of serum bactericidal or agglutinating activity. Preincubation with purified homologous or heterologous LPS did not prevent adherence, suggesting that LPS was not acting as an adhesin per se. Nevertheless, these findings raise the possibility that oral administration of preparations containing anti-LPS may interfere with colonization of the human gut by STEC, and therefore could be of potential therapeutic value if administered early in the course of infection.

Diarrheagenic Escherichia coli

Escherichia coli is the predominant nonpathogenic facultative flora of the human intestine. Some E. coli strains, however, have developed the ability to cause disease of the gastrointestinal, urinary, or central nervous system in even the most robust human hosts. Diarrheagenic strains of E. coli can be divided into at least six different categories with corresponding distinct pathogenic schemes. Taken together, these organisms probably represent the most common cause of pediatric diarrhea worldwide. Several distinct clinical syndromes accompany infection with diarrheagenic E. coli categories, including traveler's diarrhea (enterotoxigenic E. coli), hemorrhagic colitis and hemolytic-uremic syndrome (enterohemorrhagic E. coli), persistent diarrhea (enteroaggregative E. coli), and watery diarrhea of infants (entero-pathogenic E. coli). This review discusses the current level of understanding of the pathogenesis of the diarrheagenic E. coli strains and describes how their pathogenic schemes underlie the clinical manifestations, diagnostic approach, and epidemiologic investigation of these important pathogens.

Shiga toxin-producing Escherichia coli isolates from cases of human disease show enhanced adherence to intestinal epithelial (Henle 407) cells

Shiga toxin-producing Escherichia coli (STEC) strains are a diverse group of organisms which are known to cause diarrhea and hemorrhagic colitis in humans. We have recently described a large food-borne outbreak of STEC disease caused by contaminated semidry fermented sausage (A. W. Paton, R. Ratcliff, R. M. Doyle, J. Seymour-Murray, D. Davos, J. A. Lanser, and J. C. Paton, J. Clin. Microbiol. 34:1622-1627, 1996). STEC strains belonging to several O serotypes were isolated from the contaminated food source, but of these, only a subset were isolated from patients with diarrhea or hemolytic-uremic syndrome (HUS). In the present study, we characterized these STEC isolates with respect to the presence of putative virulence-associated genes and the capacity to adhere to a human intestinal epithelial cell line (Henle 407). The O111:H- STEC strain 95NR1 (isolated from one of the outbreak HUS patients) was shown to adhere to Henle 407 cells in a dose-dependent, mannose-resistant fashion. Microscopic examination revealed a diffuse pattern of adherence for this as well as several other STEC strains. Interestingly, the adherence of STEC strains from HUS cases (both outbreak related and sporadic) was significantly greater than that of STEC strains found in the contaminated food source but not found in any patients. These studies support the hypothesis that an enhanced capacity to adhere to intestinal cells is one of the factors which distinguishes human-virulent STEC strains from those of lesser clinical significance.

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.