Characteristics of alpha-hemolytic strains of Escherichia coli isolated from dogs with gastroenteritis

Detection of Shiga Toxin-Producing Escherichia coli from Nonhuman Sources and Strain Typing

Shiga toxin-producing Escherichia coli (STEC) strains are commonly found in the intestine of ruminant species of wild and domestic animals. Excretion of STEC with animal feces results in a broad contamination of food and the environment. Humans get infected with STEC through ingestion of contaminated food, by contact with the environment, and from STEC-excreting animals and humans. STEC strains can behave as human pathogens, and some of them, called enterohemorrhagic E. coli (EHEC), may cause hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS). Because of the diversity of STEC types, detection strategies for STEC and EHEC are based on the identification of Shiga toxins or the underlying genes. Cultural enrichment of STEC from test samples is needed for identification, and different protocols were developed for this purpose. Multiplex real-time PCR protocols (ISO/CEN TS13136 and USDA/FSIS MLG5B.01) have been developed to specifically identify EHEC by targeting the LEE (locus of enterocyte effacement)-encoded eae gene and genes for EHEC-associated O groups. The employment of more genetic markers (nle and CRISPR) is a future challenge for better identification of EHEC from any kinds of samples. The isolation of STEC or EHEC from a sample is required for confirmation, and different cultivation protocols and media for this purpose have been developed. Most STEC strains present in food, animals, and the environment are eae negative, but some of these strains can cause HC and HUS in humans as well. Phenotypic assays and molecular tools for typing EHEC and STEC strains are used to detect and characterize human pathogenic strains among members of the STEC group.

Structural studies and biosynthetic aspects of the O-antigen polysaccharide from Escherichia coli O42

The structure of the O-antigen polysaccharide (PS) from Escherichia coli O42 has been investigated by NMR spectroscopy as the main method, which was complemented with sugar analysis, mass spectrometry, and analysis of biosynthetic information. The O-specific chain of the O-deacylated lipopolysaccharide (LPS-OH) consists of branched tetrasaccharide-glycerol repeating units joined by phosphodiester linkages. The lipid-free polysaccharide contains 0.8equiv of O-acetyl groups per repeating unit and has the following teichoic acid-like structure: Based on biosynthetic aspects, this should also be the biological repeating unit. This O-antigen structure is remarkably similar to that of E. coli O28ac, differing only in the presence or absence, respectively, of a glucose residue at the branching point. The structural similarity explains the serological cross-reactivity observed between strains of these two serogroups, and also their almost identical O-antigen gene cluster sequences.

Different assay conditions for detecting the production and release of heat-labile and heat-stable toxins in enterotoxigenic Escherichia coli isolates

Enterotoxigenic Escherichia coli (ETEC) produce heat-labile (LT) and/or heat-stable enterotoxins (ST). Despite that, the mechanism of action of both toxins are well known, there is great controversy in the literature concerning the in vitro production and release of LT and, for ST, no major concerns have been discussed. Furthermore, the majority of published papers describe the use of only one or a few ETEC isolates to define the production and release of these toxins, which hinders the detection of ETEC by phenotypic approaches. Thus, the present study was undertaken to obtain a better understanding of ST and LT toxin production and release under laboratory conditions. Accordingly, a collection of 90 LT-, ST-, and ST/LT-producing ETEC isolates was used to determine a protocol for toxin production and release aimed at ETEC detection. For this, we used previously raised anti-LT antibodies and the anti-ST monoclonal and polyclonal antibodies described herein. The presence of bile salts and the use of certain antibiotics improved ETEC toxin production/release. Triton X-100, as chemical treatment, proved to be an alternative method for toxin release. Consequently, a common protocol that can increase the production and release of LT and ST toxins could facilitate and enhance the sensitivity of diagnostic tests for ETEC using the raised and described antibodies in the present work.

Frequency of Detection of Escherichia coli, Salmonella spp., and Campylobacter spp. in the Faeces of Wild Rats (Rattus spp.) in Trinidad and Tobago

The study was conducted to determine the frequency of isolation of Salmonella, Campylobacter and E. coli O157 in the faecal samples of rats trapped across the regional corporations in Trinidad and to assess their resistance to antimicrobial agents. A total of 204 rats were trapped for the detection of selected bacteria. Standard methods were used to isolate Salmonella, Campylobacter and E. coli O157. Characterization of E. coli was done on sorbitol MacConkey agar to determine non-sorbitol fermentation, blood agar to determine haemolytic and mucoid colonies and by using E. coli O157 antiserum to determine O157 strain. The disc diffusion method was used to determine resistance to nine antimicrobial agents. Of the 204 rats, 4 (2.0%), 7 (3.4%) and 171 (83.8%) were positive for Salmonella spp., Campylobacter spp. and E. coli, respectively. Of the 171 isolates of E. coli tested 0 (0.0%), 25 (14.6%) and 19 (11.1%) were haemolytic, mucoid and non-sorbitol fermenters, respectively. All isolates were negative for the O157 strain. The frequency of resistance to the 9 antimicrobial agents tested was 75% (3 of 4) for Salmonella, 85.7% (6 of 7) of Campylobacter spp. and 36.3% (62 of 171) for E. coli (P < .05; χ(2)).

Common origin of plasmid encoded alpha-hemolysin genes in Escherichia coli

BACKGROUND

Alpha (alpha)-hemolysin is a pore forming cytolysin and serves as a virulence factor in intestinal and extraintestinal pathogenic strains of E. coli. It was suggested that the genes encoding alpha-hemolysin (hlyCABD) which can be found on the chromosome and plasmid, were acquired through horizontal gene transfer. Plasmid-encoded alpha-hly is associated with certain enterotoxigenic (ETEC), shigatoxigenic (STEC) and enteropathogenic E. coli (EPEC) strains. In uropathogenic E. coli (UPEC), the alpha-hly genes are located on chromosomal pathogenicity islands. Previous work suggested that plasmid and chromosomally encoded alpha-hly may have evolved independently. This was explored in our study.

RESULTS

We have investigated 11 alpha-hly plasmids from animal and human ETEC, STEC and EPEC strains. The size of alpha-hly plasmids ranges from 48-157 kb and eight plasmids are conjugative. The regulatory gene (hlyR) located upstream of the hlyCABD gene operon and an IS911 element located downstream of hlyD are conserved. Chromosomally-encoded alpha-hly operons lack the hlyR and IS911 elements. The DNA sequence of hlyC and hlyA divided the plasmid- and chromosomally-encoded alpha-hemolysins into two clusters. The plasmid-encoded alpha-hly genes could be further divided into three groups based on the insertion of IS1 and IS2 in the regulatory region upstream of the alpha-hly operon. Transcription of the hlyA gene was higher than the housekeeping icdA gene in all strains (rq 4.8 to 143.2). Nucleotide sequence analysis of a chromosomally located alpha-hly determinant in Enterobacter cloacae strain indicates that it originates from an E. coli alpha-hly plasmid.

CONCLUSION

Our data indicate that plasmids encoding alpha-hly in E. coli descended from a common ancestor independent of the plasmid size and the origin of the strains. Conjugative plasmids could contribute to the spread of the alpha-hly determinant to Enterobacter cloacae. The presence of IS-elements flanking the plasmid-encoded alpha-hly indicate that they might be mobile genetic elements.

Sequence analysis of the Escherichia coli O15 antigen gene cluster and development of a PCR assay for rapid detection of intestinal and extraintestinal pathogenic E. coli O15 strains

A collection of 33 Escherichia coli serogroup O15 strains was studied with regard to O:H serotypes and virulence markers and for detection of the O-antigen-specific genes wzx and wzy. The strains were from nine different countries, originated from healthy or diseased humans and animals and from food, and were isolated between 1941 and 2003. On the basis of virulence markers and clinical data the strains could be split into different pathogroups, such as uropathogenic E. coli, enteropathogenic E. coli, Shiga toxin-producing E. coli, and enteroaggregative E. coli. H serotyping and genotyping of the flagellin (fliC) gene revealed 11 different H types and a close association between certain H types, virulence markers, and pathogroups was found. Nucleotide sequence analysis of the O-antigen gene cluster revealed putative genes for biosynthesis of O15 antigen. PCR assays were developed for sensitive and specific detection of the O15-antigen-specific genes wzx and wzy. The high pathotype diversity found in the collection of 33 O15 strains contrasted with the high level of similarity found in the genes specific to the O15 antigen. This might indicate that the O15 determinant has been spread by horizontal gene transfer to a number of genetically unrelated strains of E. coli.

Prevalence of enteropathic Escherichia coli in dogs with acute and chronic diarrhoea

Samples of faeces from 57 dogs with acute diarrhoea, 82 dogs with chronic diarrhoea, 34 clinically healthy household dogs and 88 kennelled control dogs were analysed by hybridisation, using DNA probes to detect enteropathogenic Escherichia coli (EPEC) and enterotoxigenic E coli (ETEC), verocytotoxin-producing E coli (VTEC), enterohaemorrhagic E coli (EHEC), enteroinvasive E coli (EIEC) and enteroaggregative E coli (EAggEC). Samples of duodenal juice from 60 of the 82 dogs with chronic diarrhoea were also examined. Significantly more of the dogs with diarrhoea were excreting EPEC (acute 35.1 per cent, chronic 31.7 per cent) and VTEC (acute 24.6 per cent, chronic 28 per cent) than the kennelled dogs (EPEC 17.1 per cent, VTEC 0 per cent) or the household control dogs (EPEC 6 per cent, VTEC 5.9 per cent). Enteropathic E coli was also detected in the duodenal juice of 23 of 60 (38.3 per cent) of the dogs with chronic diarrhoea. The EPEC attaching and effacing A (eaeA) gene and the verocytotoxin 1 (VR1) gene coding for VTEC were often found together. There was good agreement between in vitro studies and hybridisation for the detection of eaeA and VT1. Isolates from the dogs with diarrhoea adhered significantly more to Hep-2 cells, and VT1-positive strains from the dogs with diarrhoea consistently killed more than 50 per cent of Vero cells.

Bacterial-associated diarrhea in the dog: a critical appraisal

The clinical documentation of enteropathogenic bacteria causing diarrhea in dogs is clouded by the presence of many of these organisms existing as normal constituents of the indigenous intestinal flora. The diagnosis of a putative bacterial enteropathogen(s) in dogs should be made based on a combination of parameters, including signalment and predisposing factors, clinical signs, serologic assays for toxins, fecal culture, and PCR. Relying on results of fecal culture alone is problematic, because C perfringens, C difficile, Campylobacter spp, and pathogenic and non-pathogenic E coli are commonly isolated from apparently healthy dogs [10,13,33]. Nevertheless, culture may be useful in procuring isolates for the application of molecular techniques, such as PCR, for detection of specific toxin genes or molecular typing of isolated strains to establish clonality in suspected outbreaks. The oversimplistic attempt to characterize bacterially associated diarrhea by anatomic localization of clinical signs should be discouraged, because most of the previously mentioned bacteria have been associated with small and large intestinal diarrhea. Accurate diagnosis of infections may require diagnostic laboratories to incorporate PCR-based assays using genus- and species-specific primers to facilitate detection of toxin genes and differentiation of species that appear phenotypically and biochemically similar. There has been tremendous interest in the application of microarray technology for the simultaneous detection of thousands of genes or target DNA sequences on one glass slide. This powerful tool could be used for detection of specific pathogenic bacterial strains in fecal specimens obtained from dogs in the future.

Haemolytic Escherichia coli isolated from dogs with diarrhea have characteristics of both uropathogenic and necrotoxigenic strains

Twenty-four haemolytic Escherichia coli strains were isolated from dogs with diarrhea. The strains were serotyped and analysed by polymerase chain reaction (PCR) for genes encoding virulence factors associated with E. coli that cause diarrhea in animals. Adhesion antigen production was deduced from haemagglutination experiments. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of heat extracts was also used as an indication for the production of adhesive structures. The majority of the strains was shown to produce this type of virulence factor. Adhesion and invasion tests of the strains and Caco-2 cells showed that all strains adhered and that two were invasive. The two invasive strains were positive in the intimin PCR and one of them also contained genes encoding CS31A. The PCR for heat stable toxin (ST) was positive in only four strains, as was the presence of F17 fimbrial genes. Surprisingly, 19 strains had intact P fimbrial operons, coding for an adhesin involved in urinary tract infection (UTI). The cytotoxic necrotising factor 1 (CNF1) gene, also mainly found in UTI was likewise detected in these 19 strains. Cytolethal distending toxin (Cdt) genes were found in five strains. The high number of strains positive for CNF1 and P fimbriae prompted us to test the strains in a multiplex PCR used to test E. coli isolated from UTI in various species for 30 virulence associated genes. The data showed that the majority of the diarrhea isolates have virulence factor profiles highly similar to UTI E. coli isolates from dogs. This raises the question whether these isolates are real intestinal pathogens or "innocent bystanders". However, since CNF1 producing necrotoxic E. coli (NTEC) strains isolated from humans, pigs and calves with diarrhea appear to be highly related to our strains, it might be that in dogs this type of isolate is capable of causing not only UTI, but also diarrhea. If this is the case and this type of isolate is "bifunctional", domestic animals likely constitute a reservoir of NTEC strains which can be also pathogenic for humans.

Characterization of Escherichia coli isolated from healthy dogs

Five month old dogs from a Midwestern research kennel occasionally developed bloody diarrhea after shipment to other facilities. As previous diagnostic efforts failed to reveal any potential pathogens in feces from normal and diarrheic dogs, Escherichia coli was investigated for select virulence properties that may contribute to the occurrence of bloody diarrhea. Fecal swabs from 52 healthy dogs were examined for E. coli. Two hundred and sixty E. coli-like colonies were screened by PCR for the attaching and effacing (eae) gene, Shiga toxin (stx) genes, and the heat-stable enterotoxin type A (sta) gene. One hundred forty two of the 260 E. coli-like colonies (54.6%) from 43 dogs were eae or sta positive; and 60 of the eae and/or sta positive isolates were examined further. Among the 60 isolates, 23 (38.3%) possessed the eae gene, 32 (53.3%) possessed the sta gene, and five (8.3%) possessed both eae and sta genes (eae+/sta+). Of the 60 isolates, six sta+ and one eae+/sta+ isolates were hemolytic. When examined in the suckling mouse assay, five of six sta+ isolates and three of four eae+/sta+ isolates gave gut-to-remaining carcass ratios > or =0.083, indicating expression of heat-stable enterotoxin. These enterotoxin-producing isolates belonged to serogroups O42, O170, and O-negative.

Characterization of the roles of hemolysin and other toxins in enteropathy caused by alpha-hemolytic Escherichia coli linked to human diarrhea

Escherichia coli strains producing alpha-hemolysin have been associated with diarrhea in several studies, but it has not been clearly demonstrated that these strains are enteropathogens or that alpha-hemolysin is an enteric virulence factor. Such strains are generally regarded as avirulent commensals. We examined a collection of diarrhea-associated hemolytic E. coli (DHEC) strains for virulence factors. No strain produced classic enterotoxins, but they all produced an alpha-hemolysin that was indistinguishable from that of uropathogenic E. coli strains. DHEC strains also produced other toxins including cytotoxic necrotizing factor 1 (CNF1) and novel toxins, including a cell-detaching cytotoxin and a toxin that causes HeLa cell elongation. DHEC strains were enteropathogenic in the RITARD (reversible intestinal tie adult rabbit diarrhea) model of diarrhea, causing characteristic enteropathies, including inflammation, necrosis, and colonic cell hyperplasia in both small and large intestines. Alpha-hemolysin appeared to be a major virulence factor in this model since it conferred virulence to nonpathogenic E. coli strains. Other virulence factors also appear to be contributing to virulence. These findings support the epidemiologic link to diarrhea and suggest that further research into the role of DHEC and alpha-hemolysin in enteric disease is warranted.

Distribution and characterization of faecal necrotoxigenic Escherichia coli CNF1+ and CNF2+ isolated from healthy cows and calves

Faecal swabs obtained from a random sample of 268 cows and 90 calves on 19 Lugo (northwestern Spain) farms were examined for necrotoxigenic Escherichia coli (NTEC) producing the cytotoxic necrotizing factors type 1 (CNF1) and type 2 (CNF2). We found NTEC CNF1+ and CNF2+ on 11% and 95% of the farms, respectively, NTEC producing CNF2 were significantly more frequently isolated from calves (58%) than from cows (17%) (P < 0.001). The proportion of animals colonized with CNF2+ strains on each farm ranged from 0% to 60%. NTEC strains producing CNF2 isolated from healthy cattle belonged to 27 O serogroups; however, 64% were of one of 12 serogroups (O2, O8, O8-O75, O14, O15, O55, O86, O88, O115, O121, O147, and O168). Furthermore, the serogroups determined in CNF2+ strains isolated from cows (O2, O8, and O14) were different from those found in NTEC producing CNF2 isolated from calves (O8-O75, O15, O55, O86, O88, O115 and O147).

Microbiological analysis of 'black pudding', a Trinidadian delicacy and health risk to consumers

The prevalences of Salmonella, Escherichia coli and Staphylococcus aureus in black pudding which originated from local vendors and supermarkets in Trinidad were determined. The enterotoxigenicity of S. aureus strains and occurrence of O157:H7 strains amongst E. coli isolates were also investigated. For the 100 black puddings each sampled from supermarkets and vendors, the mean total aerobic plate count (TAPC) per g was 1.8 x 10(7) +/- 1.5 x 10(7) and 1.5 x 10(8) +/- 2.3 x 10(8), respectively. E. coli was isolated from 56 (56.0%) black pudding samples from supermarkets with a mean count per g of 9.2 x 10(6) +/- 7.9 x 10(6) compared to a prevalence of 79% (79 of 100) and mean count per g of 3.2 x 10(7) +/- 4.7 x 10(7) for samples from local vendors. The difference between prevalences was statistically significant (P < or = 0.001; chi 2). Only 1 (2.2%) of 45 strains of E. coli from supermarket-purchased pudding tested, was an 0157:H7 strain compared to 9 (13.6%) of 66 strains of E. coli from vendor-sold black pudding. The difference was not statistically significant (P > or = 0.05; chi 2). Five (5.0%) of 100 black pudding samples from supermarkets yielded Salmonella, with S. ohio being the predominant serotype. For vendor-sold black pudding however, 11 (11.0%) samples were positive for Salmonella with a new serotype, S. unnamed (4,12:d-) being responsible for 50% (6 of 12) of isolates from this source. Forty samples each of black pudding from supermarkets and vendors were all (100.0%) positive for S. aureus with mean counts per g being 3.1 x 10(5) +/- 8.8 x 10(5) and 3.3 x 10(6) +/- 7.7 x 10(6), respectively. Overall, 27 (33.8%) of 80 strains of S. aureus tested were enterotoxigenic producing staphylococcal enterotoxins A(SEA), SEB, SEC, SED or a combination. It was concluded that black pudding poses a high risk to consumers based on the prevalence, microbial load and toxigenicity of the pathogens detected.

Characterization of Escherichia coli isolated from foals

Serotype, biotype, antibiogram, hemolysin production, fimbrial hemagglutinins, select toxin genes (STb, STaP, LT, slt1 and slt2) and the attaching effacing (eae) gene were determined for 99 foal strains of E. coli. E. coli from diarrheic and normal foals could not be distinguished by serotype, biotype, or antibiogram. Differences (P < or = 0.05) were observed in hemolysin production (11.5% vs 0%) and the expression of mannose-resistant hemagglutinins (23% vs 13%) among E. coli from diarrheic and healthy foals, respectively. Three of the E. coli strains from diarrheic foals were positive with probes for slt genes and one was positive for STb and LT genes. One strain from a healthy foal possessed the STb gene. As determined by the polymerase chain reaction, 8 strains possessed the eae gene. Seven of the 8 strains were from diarrheic foals and one eae-positive strain was from a healthy foal. The slt-positive strains did not possess eae genes and the eae-positive strains did not possess slt genes. These results indicate that enterotoxigenic strains of E. coli are not implicated in any substantial degree in sporadic foal diarrhea. However, the identification of slt-positive and eae-positive strains in foal feces indicate the presence of potentially virulent strains among foals.

Restriction Fragment Length Polymorphisms Associated with α-Hemolysin Determinants are Correlating with the Expression of α-Hemolysin in Strains of Escherichia coli

Three different phenotypes of hemolysis on blood-agar were detected when 58 isolates of Escherichia coli were investigated for alpha-hemolysin synthesis. In strains with chromosomally encoded alpha-hly genes, phenotype I (large and clear hemolysis zones) corresponded with high hemolytic activity and with a 17.2 kb size BamHI restriction fragment hybridizing with an alpha-hly-specific gene probe. Phenotype II (small and turbid hemolysis zones) was associated with low hemolytic activity and generally with a 12.8 kb size hybridizing BamHI restriction fragment. An intermediate phenotype (type I/II) was found in a few strains with moderate hemolytic activity. This correlation between hemolytic phenotype and activity was not found in E. coli carrying alpha-hly plasmids. Type I strains differed from all others in the promotor region of their 17.2 kb size BamHI fragment associated chromosomal alpha-hly determinant. The relation between hemolytic phenotype and DNA hybridization pattern was found in unrelated E. coli isolates of human and animal origin. An association of alpha-hemolysin with other virulence factors was found in most strains of all three phenotypes.