Polymerase chain reaction for detection of Escherichia coli strains producing cytotoxic necrotizing factor type 1 and type 2 (CNF1 and CNF2)

Molecular Markers and Antimicrobial Resistance Patterns of Extraintestinal Pathogenic Escherichia coli from Camel Calves Including Colistin-Resistant and Hypermucoviscuous Strains

Extraintestinal pathogenic Escherichia coli (ExPEC) strains are capable of causing various systemic infections in both humans and animals. In this study, we isolated and characterized 30 E. coli strains from the parenchymatic organs and brains of young (<3 months of age) camel calves which died in septicemia. Six of the strains showed hypermucoviscous phenotype. Based on minimum inhibitory concentration (MIC) values, seven of the strains were potentially multidrug resistant, with two additional showing colistin resistance. Four strains showed mixed pathotypes, as they carried characteristic virulence genes for intestinal pathotypes of E. coli: three strains carried cnf1, encoding cytotoxic necrotizing factor type 1, the key virulence gene of necrotoxigenic E. coli (NTEC), and one carried eae encoding intimin, the key virulence gene of enteropathogenic E. coli (EPEC). An investigation of the integration sites of pathogenicity islands (PAIs) and the presence of prophage-related sequences showed that the strains carry diverse arrays of mobile genetic elements, which may contribute to their antimicrobial resistance and virulence patterns. Our work is the first to describe ExPEC strains from camels, and points to their veterinary pathogenic as well as zoonotic potential in this important domestic animal.

Relating Antimicrobial Resistance and Virulence in Surface-Water E. coli

The role of the environment in the emergence and spread of antimicrobial resistance (AMR) is being increasingly recognized, raising questions about the public health risks associated with environmental AMR. Yet, little is known about pathogenicity among resistant bacteria in environmental systems. Existing studies on the association between AMR and virulence are contradictory, as fitness costs and genetic co-occurrence can be opposing influences. Using Escherichia coli isolated from surface waters in eastern North Carolina, we compared virulence gene prevalence between isolates resistant and susceptible to antibiotics. We also compared the prevalence of isolates from sub-watersheds with or without commercial hog operations (CHOs). Isolates that had previously been evaluated for phenotypic AMR were paired by matching isolates resistant to any tested antibiotic with fully susceptible isolates from the same sample date and site, forming 87 pairs. These 174 isolates were evaluated by conventional PCR for seven virulence genes (bfp, fimH, cnf-1, STa (estA), EAST-1 (astA), eae, and hlyA). One gene, fimH, was found in 93.1% of isolates. Excluding fimH, at least one virulence gene was detected in 24.7% of isolates. Significant negative associations were found between resistance to at least one antibiotic and presence of at least one virulence gene, tetracycline resistance and presence of a virulence gene, resistance and STa presence, and tetracycline resistance and STa presence. No significant associations were found between CHO presence and virulence, though some sub-significant associations merit further study. This work builds our understanding of factors controlling AMR dissemination through the environment and potential health risks.

Characterization of multidrug-resistant avian pathogenic Escherichia coli: an outbreak in canaries

The canary (Serinus canaria) is appreciated for its beautiful song, colors, and docile temperament and drives a lucrative business. However, diseases caused by avian pathogenic Escherichia coli (APEC) compromise the health of canaries, and the inadequate antimicrobial treatment can lead to the emergence of resistant strains. This study aimed to characterize 21 isolates of E. coli obtained from canaries infected with colibacillosis during an outbreak in northern Paraná State, Brazil. APEC and diarrheagenic E. coli (DEC) virulence genes were screened for by polymerase chain reaction (PCR). All isolates were positive for the hlyF, iss, and ompT genes, which are characteristic of APEC. The iroN gene was found in 95.2% of isolates, and none had the iutA gene. The ipaH gene, characteristic of enteroinvasive E. coli (EIEC), was found in 71.4% of isolates, all belonging to the phylogenetic group B1. High genetic similarity (>95%) was found using enterobacterial repetitive intergenic consensus PCR (ERIC-PCR). The isolates belonged to serotypes O117:H4 (71.4%) and O1:H20 (23.8%). This is the first report of a clonal colibacillosis outbreak in canaries caused by APEC. All isolates were resistant to ampicillin, nalidixic acid, ciprofloxacin, enrofloxacin, norfloxacin, and tetracycline. The high rate of multidrug resistance in our study shows the importance of avoiding the inadequate antibiotic treatment. We suggest that further studies should be conducted to contribute to the understanding of colibacillosis in canaries since the health of animals is linked to human and environmental health, as defined by the concept of One Health.

Cytotoxic Escherichia coli strains encoding colibactin and cytotoxic necrotizing factor (CNF) colonize laboratory macaques

Background

Many Escherichia coli strains are considered to be a component of the normal flora found in the human and animal intestinal tracts. While most E. coli strains are commensal, some strains encode virulence factors that enable the bacteria to cause intestinal and extra-intestinal clinically-relevant infections. Colibactin, encoded by a genomic island (pks island), and cytotoxic necrotizing factor (CNF), encoded by the cnf gene, are genotoxic and can modulate cellular differentiation, apoptosis and proliferation. Some commensal and pathogenic pks+ and cnf+ E. coli strains have been associated with inflammation and cancer in humans and animals.

Results

In the present study, E. coli strains encoding colibactin and CNF were identified in macaque samples. We performed bacterial cultures utilizing rectal swabs and extra-intestinal samples from clinically normal macaques. A total of 239 E. coli strains were isolated from 266 macaques. The strains were identified biochemically and selected isolates were serotyped as O88:H4, O25:H4, O7:H7, OM:H14, and OM:H16. Specific PCR for pks and cnf1 gene amplification, and phylogenetic group identification were performed on all E. coli strains. Among the 239 isolates, 41 (17.2%) were pks+/cnf1−, 19 (7.9%) were pks−/cnf1+, and 31 (13.0%) were pks+/cnf1+. One hundred forty-eight (61.9%) E. coli isolates were negative for both genes (pks−/cnf1−). In total, 72 (30.1%) were positive for pks genes, and 50 (20.9%) were positive for cnf1. No cnf2+ isolates were detected. Both pks+ and cnf1+ E. coli strains belonged mainly to phylogenetic group B2, including B2₁. Colibactin and CNF cytotoxic activities were observed using a HeLa cell cytotoxicity assay in representative isolates. Whole genome sequencing of 10 representative E. coli strains confirmed the presence of virulence factors and antibiotic resistance genes in rhesus macaque E. coli isolates.

Conclusions

Our findings indicate that colibactin- and CNF-encoding E. coli colonize laboratory macaques and can potentially cause clinical and subclinical diseases that impact macaque models.

Electronic supplementary material

The online version of this article (10.1186/s13099-017-0220-y) contains supplementary material, which is available to authorized users.

Antimicrobial resistance in diarrheagenic Escherichia coli from ready-to-eat foods

Certain subgroups of Escherichia coli have congenital or acquired virulence properties that allow them to cause a wide spectrum of disease. The aim of this study was to investigate the occurrence of diarrheagenic E. coli strains in ready-to-eat (RTE) foods produced in institutional, commercial and hotel restaurants in Salvador, Brazil. The presence of virulent isolates and antimicrobial resistance were evaluated. Four hundred forty-six samples were collected and grouped into cereals and vegetables, meat-based preparations, cooked salads, raw salads, garnishes, soups and sauces, desserts and juices. E. coli were detected using the most probable number method, the presence of virulence factors in isolates was determined by polymerase chain reaction (PCR) assays, and antibiotic resistance was analyzed using the disc diffusion method. In total, 15 isolates (3.1%) of E. coli were recovered; raw salads had the highest detection rate, 1.4%, followed by cooked salads, 0.8%; meat-based preparations, 0.4%; and cereals and vegetables, 0.4%. PCR assays showed that none of the isolates had the virulence genes cnf1, cnf2, eae, sta, lt1, stx1, stx2 or cdtB. The isolates showed resistance to nine antibiotics of the 15 tested, and the highest levels of resistance were found for sulfamethoxazole/trimethoprim, tetracycline, ampicillin, and chloramphenicol (13.3% of isolates for each antibiotic). One isolate from cooked salad had plasmid-mediated multidrug resistance to tetracycline, trimethoprim/sulfamethoxazole, ampicillin and chloramphenicol. These results suggest that RTE foods, especially raw salads, can be reservoirs of E. coli and facilitate the spread of antibiotic resistance genes to the gastrointestinal microbiota of humans.

Association between virulence profile, biofilm formation and phylogenetic groups of Escherichia coli causing urinary tract infection and the commensal gut microbiota: A comparative analysis

Variety of virulence factors are involved in the pathogenicity of Escherichia coli, the common cause of the urinary tract infections (UTIs). The aim of this study was to determine some virulence factors involved in the pathogenicity and the phylogenetic grouping of E. coli from UTIs compared with the E. coli isolates from gut microbiota (fecal flora). The isolates were tested for biofilm formation, haemagglutination, cell surface hydrophobicity (CSH), hemolysin production, phylogenetic grouping and the distribution of 6 known virulence genes. Isolates from UTIs showed a significantly higher prevalence of haemagglutination and hemolysin production compared with fecal flora (P ≤ 0.05), while biofilm formation and cell surface hydrophobicity (CSH) were not significantly different among the groups. Prevalence of virulence genes fimH, kpsMT ll, iutA, sat, hlyA, and cnf1 among all isolates were: 94.5%, 66.95%, 67.8%, 39%, 23.07% and 21.08%, respectively. The genes for hlyA, cnf1, kpsMT ll were found to be higher in UTI isolates compared to fecal flora (P ≤ 0.05). The frequency of the isolates in the phylogenetic groups B2, D, A and B1 were 36.7%, 31.3%, 16.2% and 15.6%, respectively. All the virulence genes except fimH were found to be significantly higher in the isolates of groups B2 and D. The results suggests that certain factors are necessary for the host colonization and infection and they are common in both virulent and non-virulent strains, and that the strains in the groups A and B1 having the lower virulence factors must acquire these factors when the condition is in favor of their dissemination to the urinary tract. In contrast the isolates in the groups B2 and D appeared to be potentially virulent.

Characterization of virulence factors and phylogenetic group determination of Escherichia coli isolated from diarrheic and non-diarrheic calves from Brazil

This study aimed to detect virulence factors, pathovars, and phylogenetic groups of Escherichia coli strains obtained from feces of calves with and without diarrhea up to 70 days old and to determine the association between occurrence of diarrhea, phylogenetic groups, and pathovars. Phylo-typing analysis of the 336 E. coli strains isolated from calves with Clermont method showed that 21 (6.25 %) belong to phylogroup A, 228 (67.85 %) to phylogroup B1, 2 (0.6 %) to phylogroup B2, 5 (1.49 %) to phylogroup C, 57 (16.96 %) to phylogroup E, and 3 (0.9 %) to phylogroup F. Phylogroup D was not identified and 20 strains (5.95 %) were assigned as "unknown." The distribution of phylogenetic groups among pathovars showed that NTEC belong to phylogroups B1 (17) and C (4); EPEC to phylogroups B1 (6) and E (8); STEC to phylogroups A (5), B1 (56), B2 (2), C (1), and E (15); EHEC to phylogroups B1 (95) and E (5); and ETEC to phylogroups A (3), B1 (7), and E (10). The EAST-1 strains were phylogroups A (13), B1 (47), E (19), and F (3); E. coli strains of "unknown" phylogroups belonged to pathovars EPEC (1), EHEC (2), STEC (7), and EAST-1 strains (6). ETEC was associated with diarrhea (P = 0.002). Our study did not find association between the phylogenetic background and occurrence of diarrhea (P = 0.164) but did find some relationship in phylogenetic group and pathovar. The study showed that EHEC and STEC are classified as phylogroup B1, EAST-1 phylogroup A, ETEC, and EPEC phylogroup E.

Presence of pathogenicity islands and virulence genes of extraintestinal pathogenic Escherichia coli (ExPEC) in isolates from avian organic fertilizer

Poultry litter is commonly used as fertilizer in agriculture. However, this poultry litter must be processed prior to use, since poultry have a large number of pathogenic microorganisms. The aims of this study were to isolate and genotypically and phenotypically characterize Escherichia coli from avian organic fertilizer. Sixty-four E. coli isolates were identified from avian organic fertilizer and characterized for ExPEC virulence factors, pathogenicity islands, phylogenetic groups, antimicrobial resistance, biofilm formation, and adhesion to HEp-2 cells. Sixty-three isolates (98.4%) showed at least one virulence gene (fimH, ecpA, sitA, traT, iutA, iroN, hlyF, ompT and iss). The predominant phylogenetic groups were groups A (59.3%) and B1 (34.3%). The pathogenicity island CFT073II (51.5%) was the most prevalent among the isolates tested. Thirty-two isolates (50%) were resistant to at least one antimicrobial agent. Approximately 90% of isolates adhered to HEp-2 cells, and the predominant pattern was aggregative adherence (74.1%). In the biofilm assay, it was observed that 75% of isolates did not produce biofilm. These results lead us to conclude that some E. coli isolates from avian organic fertilizer could be pathogenic for humans.

Virulence factors, serogroups and antimicrobial resistance properties of Escherichia coli strains in fermented dairy products

Background

From a clinical perspective, it is essential to know the microbial safety of fermented dairy products. Doogh and kashk are fermented dairies. These products are used by millions of people but their microbial qualities are unknown. Shiga toxin producing Escherichia coli (STEC) is one of the most commonly detected pathogens in the cases of food poisoning and food-borne illnesses. The present investigation was carried out in order to study the molecular characterization and antimicrobial resistance properties of STEC strains isolated from fermented dairy products.

Methods

Six hundred fermented dairy samples were collected and immediately transferred to the laboratory. All samples were cultured immediately and those that were E. coli-positive were analyzed for the presence of O157 , O26, O103, O111, O145, O45, O91, O113, O121 and O128 STEC serogroups, tetA, tetB, blaSHV, CITM, cmlA, cat1, aadA1, dfrA1, qnr, aac (3)-IV, sul1 and ereA antibiotic resistance genes and stx1, stx2, eaeA, ehly, cnf1, cnf2, iutA, cdtB, papA, traT, sfaS and fyuA virulence factors using PCR. Antimicrobial susceptibility testing was performed also using disk diffusion methodology with Mueller–Hinton agar.

Results

Fifty out of 600 (8.33%) dairy samples harbored E. coli. In addition, yoghurt was the most commonly contaminated dairy. O157 (26%) and O26 (12%) were the most commonly detected serogroups. A significant difference was found between the frequency of Attaching and Effacing E. coli and Enterohaemorrhagic E. coli (P <0.05). Stx1 (44%), eae (36%), papA (32%) stx2 (30%), and ehly (28%) were the most commonly detected virulence factors. The genes encode resistance against tetracycline (tetA and tetB) (76% and 70%, respectively), cephalothin (blaSHV) (38%), ampicillin (CITM) (36%) and gentamicin (aac (3)-IV) (32%) were the most commonly detected. High resistance levels to tetracycline (84%), penicillin (46%), ampicillin (38%) and streptomycin (36%) were observed.

Conclusion

Fermented dairy products can easily become contaminated by antibiotic resistant STEC strains. Our findings should raise awareness about antibiotic resistance in Iran. Clinicians should exercise caution when prescribing antibiotics, especially in veterinary treatments.

Enterohemorrhagic Escherichia coli O157: H7 from healthy dairy cattle in Mid-West Brazil: occurrence and molecular characterization

Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 represents the major Shiga toxin-producing E. coli (STEC) strain related to large outbreaks and severe diseases such as hemorrhagic colitis (HC) and the potentially lethal hemolytic uremic syndrome (HUS). The aim of this study was to report the occurrence and molecular characterization of O157:H7 isolates obtained by rectal swab from 52 healthy dairy cattle belonging to 21 farms in Mid-West of Brazil. Detection of 16SrRNA, stx1, stx2, rfbO157, fliCh7, eae, ehxA, saa, cnf1, chuA, yjaA and TSPE4.C2 genes was performed by PCR. The isolates were further characterized by serotyping. Two hundred and sixty E. coli isolates were obtained, of which 126 were characterized as STEC. Two isolates from the same cow were identified as serotype O157:H7. Both isolates presented the stx2, eae, ehxA, saa and cnf1 virulence factor genes and the chuA gene in the phylogenetic classification (virulent group D), suggesting that they were clones. The prevalence of O157:H7 was found to be 1.92% (1/52 animals), demonstrating that healthy dairy cattle from farms in the Mid-West of Brazil are an important reservoir for highly pathogenic E. coli O157:H7.

Evaluation of MALDI-TOF mass spectroscopy methods for determination of Escherichia coli pathotypes

It is rapidly becoming apparent that many E. coli pathotypes cause a considerable burden of human disease. Surveillance of these organisms is difficult because there are few or no simple, rapid methods for detecting and differentiating the different pathotypes. MALDI-TOF mass spectroscopy has recently been rapidly and enthusiastically adopted by many clinical laboratories as a diagnostic method because of its high throughput, relatively low cost, and adaptability to the laboratory workflow. To determine whether the method could be adapted for E. coli pathotype differentiation the Bruker Biotyper methodology and a second methodology adapted from the scientific literature were tested on isolates representing eight distinct pathotypes and two other groups of E. coli. A total of 136 isolates was used for this study. Results confirmed that the Bruker Biotyper methodology that included extraction of proteins from bacterial cells was capable of identifying E. coli isolates from all pathotypes to the species level and, furthermore, that the Bruker extraction and MALDI-TOF MS with the evaluation criteria developed in this work was effective for differentiating most pathotypes.

Preliminary virulence genotyping and phylogeny of Escherichia coli from the gut of pigs at slaughtering stage in Brazil

In the current study we screened Escherichia coli from intestine of pigs slaughtered in Mato Grosso, Brazil, for virulence-markers related to human disease. Furthermore, we employed for the first time a phylogenetic assay to explore the association between phylogeny and virulence genotype in E. coli from finished swine. A low prevalence (7.8%) of E. coli harbouring virulence genes was observed. Among the positive isolates, 3.3% could be classified as atypical EPEC, 2.2% as STEC and 2.2% as CDT harbouring E. coli. Virulence genes were not found to co-occur in a strain. Phylogenetic determination of isolates revealed a low prevalence of E. coli lineages related to disease. Therefore, preliminary sampling of 74 pigs indicated that slaughter swine may not be major reservoirs of E. coli capable of causing human disease. In light of the significant association between phylogeny and virulence genotype, we also underscored the phylogenetic grouping of strains as a valuable tool for E. coli surveillance programmes in slaughterhouses.

Molecular characterization of Shiga toxin-producing Escherichia coli isolated from ruminant and donkey raw milk samples and traditional dairy products in Iran

The aims of the current study were to detect the virulence factors and antibiotic resistance of Shiga toxin-producing E. coli, in animal milk and dairy products in Iran. After E. coli dentification with culture method, PCR assay were developed for detection of pathogenic genes, serotypes and antibiotic resistance genes of E. coli. Results showed that out of 719 samples, 102 (14.18%) were confirmed to be positive for E. coli and out of 102 positive samples, 17.64% were O26 and 13.72% were O157 and 1.96% were O91 and 1.96% were O145 serotypes. Totally, the prevalence of stx1 and papA genes were the highest while the prevalence of sfaS and fyuA were the lowest in the positive samples. PCR results showed that tetA, tetB were the highest (64.70%) and aac(3)-IV were the lowest (27.45%) antibiotic resistant genes in E. coli positive samples. Our study indicated that the isolated E. coli trains in these regions had a highest antibiotic resistance to tetracycline (58.82%) and the lowest to nitrofurantoin (3.92%). tetA gene and E. coli O157 serotype had highest and aac(3)-IV gene, and E. coli O145 serotype had a lowest frequency rates of antibiotics resistance genes, in the region.

Diagnostic strategy for identifying avian pathogenic Escherichia coli based on four patterns of virulence genes

In order to improve the identification of avian pathogenic Escherichia coli (APEC) strains, an extensive characterization of 1,491 E. coli isolates was conducted, based on serotyping, virulence genotyping, and experimental pathogenicity for chickens. The isolates originated from lesions of avian colibacillosis (n = 1,307) or from the intestines of healthy animals (n = 184) from France, Spain, and Belgium. A subset (460 isolates) of this collection was defined according to their virulence for chicks. Six serogroups (O1, O2, O5, O8, O18, and O78) accounted for 56.5% of the APEC isolates and 22.5% of the nonpathogenic isolates. Thirteen virulence genes were more frequently present in APEC isolates than in nonpathogenic isolates but, individually, none of them could allow the identification of an isolate as an APEC strain. In order to take into account the diversity of APEC strains, a statistical analysis based on a tree-modeling method was therefore conducted on the sample of 460 pathogenic and nonpathogenic isolates. This resulted in the identification of four different associations of virulence genes that enables the identification of 70.2% of the pathogenic strains. Pathogenic strains were identified with an error margin of 4.3%. The reliability of the link between these four virulence patterns and pathogenicity for chickens was validated on a sample of 395 E. coli isolates from the collection. The genotyping method described here allowed the identification of more APEC isolates with greater reliability than the classical serotyping methods currently used in veterinary laboratories.

Molecular characterization of multidrug-resistant Escherichia coli isolates from Irish cattle farms

This study describes the genotypic characteristics of a collection of 100 multidrug-resistant (MDR) Escherichia coli strains recovered from cattle and the farm environment in Ireland in 2007. The most prevalent antimicrobial resistance identified was to streptomycin (100%), followed by tetracycline (99%), sulfonamides (98%), ampicillin (82%), and neomycin (62%). Resistance was mediated predominantly by strA-strB (92%), tetA (67%), sul2 (90%), bla(TEM) (79%), and aphA1 (63%) gene markers, respectively. Twenty-seven isolates harbored a class 1 integrase (intI1), while qacEΔ1 and sul1 markers were identified in 25 and 26 isolates, respectively. The variable regions of these integrons contained aminoglycoside, trimethoprim, and β-lactam resistance determinants (aadA12, aadB-aadA1, bla(OXA-30)-aadA1, dfrA1-aadA1, dfrA7). Class 2 integrons were identified less frequently (4%) and contained the gene cassette array dfrA1-sat1-aadA1. Resistance to ampicillin, neomycin, streptomycin, sulfonamide, and tetracycline was associated with transferable high-molecular-weight plasmids, as demonstrated by conjugation assays. A panel of virulence markers was screened for by PCR, and genes identified included vt1, K5 in 2 isolates, papC in 10 isolates, and PAI IV(536) in 37 isolates. MDR commensal E. coli isolates from Irish cattle displayed considerable diversity with respect to the genes identified. Our findings highlight the importance of the commensal microflora of food-producing animals as a reservoir of transferable MDR.

Set of virulence genes and genetic relatedness of O113 : H21 Escherichia coli strains isolated from the animal reservoir and human infections in Brazil

Escherichia coli strains of serotype O113 : H21 are commonly described as belonging to a Shiga toxin (Stx)-producing E. coli (STEC) pathotype worldwide. Albeit this STEC serotype is frequently identified among cattle and other domestic animals, to the best of our knowledge no human infections associated with STEC O113 : H21 have been registered in Brazil to date. Here, we report the virulence profile and genetic relatedness of a collection of O113 : H21 E. coli strains mainly isolated from the animal reservoir aimed at determining their potential as human pathogens. The strains from the animal reservoir (n=34) were all classified as STEC, whereas the few isolates recovered so far from human diarrhoea (n=3) lacked stx genes. Among the STEC, the stx 2d-activatable gene was identified in 85 % of the strains that also carried lpfA O113, iha, saa, ehxA, subAB, astA, cdt-V, espP, espI and epeA; the human strains harboured only lpfA O113, iha and astA. All the strains except one, isolated from cattle, were genetically classified as phylogenetic group B1. High mass plasmids were observed in 25 isolates, but only in the STEC group were these plasmids confirmed as the STEC O113 megaplasmid (pO113). Many closely related subgroups (more than 80 % similarity) were identified by PFGE, with human isolates clustering in a subgroup separate from most of the animal isolates. In conclusion, potentially pathogenic O113 : H21 STEC isolates carrying virulence markers in common with O113 : H21 clones associated with haemolytic uraemic syndrome cases in other regions were demonstrated to occur in the natural reservoir in our settings, and therefore the risk represented by them to public health should be carefully monitored.

Pyrosequencing of the Vir plasmid of necrotoxigenic Escherichia coli

Necrotoxigenic Escherichia coli, or NTEC, are defined as E. coli producing the toxin known as cytotoxic necrotizing factor, or CNF. NTEC are responsible for various diseases of humans and animals, including urinary tract infection, septicemia, and diarrhea. A subgroup of NTEC known as NTEC-2 produce a variant of CNF (CNF-2) whose gene is located on a plasmid known as Vir. Because of its involvement in NTEC-2 pathogenesis and its broad distribution among production animals, a Vir plasmid from a bovine NTEC-2 strain was sequenced and analyzed. This plasmid was found to belong to the RepFIB and RepFIIA replicon types, and it totaled 138,682 base pairs in size. Within this plasmid was an approximately 60-kb pathogenicity island, defined by its possession of multiple virulence factors within distinct genetic regions of lower G+C content bounded by inverted repeats. Within this PAI were a variety of putative virulence factors, including F17b fimbrial genes, genes of a novel fimbrial operon, tibAC, hemolysins, and the cnf2 and cdt toxin-encoding genes. The occurrence of this plasmid's virulence- and replication-associated genes was sought among a collection of 96 CNF-2-positive isolates. The most prevalent genes among this collection included repA (RepFIB), cnf2, an ompP homolog, and the tib-AC genes encoding for aggregation and biofilm formation. The Vir plasmid has evolved from an IncFIB ancestral backbone, with the RepFIB locus apparently driving the acquisition of its accessory virulence-associated elements via site-specific recombination. Overall, the completed sequence of a Vir plasmid increases our understanding of NTEC-2 pathogenomics and IncFIB plasmid evolution.

Phylogenetic background, virulence gene profiles, and genomic diversity in commensal Escherichia coli isolated from ten mammal species living in one zoo

Three hundred commensal Escherichia coli recovered from healthy herbivorous, carnivorous, and omnivorous mammals from one zoo were characterized for their phylogenetic origin, intestinal virulence gene (VG) prevalence, and genomic diversity. The phylogenetic structure of the E. coli (groups A, B1, B2, and D) from the herbivores was homogenous, with a prevailing representation of group B1. In the carnivores and omnivores, the phylogenetic diversity was species specific with a higher representation of group A compared to the herbivores. Of 16 intestinal VGs in the whole set, 8 were detected and they formed 13 VG profiles. In the herbivores, all the VG-positive isolates belonged to group B1 and harboured the genes eaeA, eastI, ehxA, stx1, and stx2, which separately or in combination formed 8 VG profiles. In the carnivores and omnivores, the VG-positive isolates frequently belonged to group A and harboured the estI and estII genes or a combination of eastI and estI, forming three VG profiles. Single genes cnf2, in group B2, and eastI, in group D, were found. Similarity analysis of pulsed-field gel electrophoresis (PFGE) patterns revealed closer relatedness between the isolates from carnivores and omnivores than those from herbivores. The comparison between the prevalence of phylogenetic groups and the phylogenetic origin of VG-positive isolates in the examined E. coli suggested, that E. coli from group B1 in herbivores and E. coli from group A rather than B1 in carnivores and omnivores are "best adapted" to the host organism. The groups revealed different preferences in the acquisition and maintenance of intestinal VGs.

Identification of virulence attributes of gastrointestinalEscherichia coliisolates of veterinary significance

The pathogenic strains ofEscherichia colirecovered from the intestinal tract of animals fall into categories called enterotoxigenic, enteropathogenic, enterohemorrhagic and necrotoxigenic. The other two categories, enteroinvasive and enteroaggregative, have not been reported in animals. The pathogenicity of these strains is determined by the presence of certain genes that encode adhesins and toxins, are generally organized in large blocks in chromosomes, large plasmids or phages, and are often transmitted horizontally between strains. In this review, we summarize current knowledge of the virulence attributes that determine the pathogenic potential ofE. colistrains and the methods available to assess the virulence of the strains. We also discuss the clinical symptoms, the gross and histological lesions, and the molecular diagnostic methods our laboratories have implemented for detecting pathogenic strains ofE. colithat are isolated from the gastrointestinal tract of animals.

Phenotypic and genetic characterization of enteropathogenic Escherichia coli (EPEC) and entero-aggregative E. coli (EAEC) from diarrhoeal and non-diarrhoeal children in Libya

A total of 50 Escherichia coli strains isolated in a Libyan hospital (20 from children with diarrhoea and 30 from healthy children) were investigated for their pathotypes and virulence traits. Altogether nine eae-positive (enteropathogenic E. coli, EPEC) and nine aggR-positive (entero-aggregative E. coli, EAEC) strains were identified. Significantly (P=0.001) more EPEC strains were identified from diarrhoeal patients (n=8) than from healthy controls (n=1), while six EAEC strains were identified from diarrhoeal and three from healthy children. Typical (eae(+), EAF(+), bfp(+)) EPEC strains (n=6) belonged to classical EPEC serogroups O55, O114, O127 and showed localized adherence on Hela cells. EAEC strains revealed genetic heterogeneity but uniformly adhered to HeLa cultures in an entero-aggregative adherence pattern. Antibiotic resistance frequently, characterized the strains. Sixty-eight percentage of the strains were resistant against at least one antibiotic and 30% harbored a class 1 integron independently of their clinical background. This is the first report from North Africa demonstrating the significance of EPEC and EAEC.

Association between cell-bound haemolysin and cell-detaching activity of Escherichia coli isolated from children

Haemolysin alpha (HlyA) produced by cell-detaching Escherichia coli, a putative new class of enteric pathogen, is considered to be the main factor responsible for detachment of cells cultured in vitro. HlyA is one of the few E. coli proteins actively secreted into the medium during exponential growth. In the present study 27 HlyA-positive E. coli isolates, randomly selected from stool specimens, produced a cell-bound haemolysin that was detectable during the exponential and stationary growth phases. The influence of both cell-free and cell-bound haemolysins of the selected isolates on cell-detaching activity of E. coli in vitro was determined. The results suggest that cell-bound haemolysin rather than cell-free HlyA was responsible for the cell-detaching activity of E. coli strains tested.

Predominance of afr2 and ral fimbrial genes related to those encoding the K88 and CS31A fimbrial adhesins in enteropathogenic Escherichia coli isolates from rabbits with postweaning diarrhea in Central Europe

PCR tests designed in these studies identified three rabbit adhesive factor genes among 43 enteropathogenic E. coli (EPEC) strains: afr1 (2 strains), the F4(K88)/CS31A-related afr2 (10 strains), and ral (15 strains). Several EPEC strains (i.e., O153:H7 and O157:H2) lacked these genes but did adhere to HeLa cells and produced attaching and effacing lesions in rabbits.

Evaluation of adherence, hemagglutination, and presence of genes codifying for virulence factors of Acinetobacter baumannii causing urinary tract infection

Acinetobacter baumannii is a strictly aerobic bacterium which causes severe infections, however its pathogenic characteristics are not well defined. Thirteen A. baumannii strains isolated from urine of hospitalized and nonhospitalized patients with different ages were investigated for the presence of virulence factors. The isolates belonged to biotypes 2, 6, and 9 and were sensitive to imipenem. The majority of them showed resistance to amikacin, ceftazidime, ceftriaxone, ciprofloxacin, gentamicin, norfloxacin, and trimethoprim-sulfamethoxazole. None of A. baumannii strains presented genes codifying for 17 different virulence factors previously described in uropathogenic Escherichia coli, when tested by polymerase chain reaction (PCR). Nine isolates agglutinated human group AB erythrocytes, in presence of mannose, but none of them agglutinated group O erythrocytes. Adherence to polystyrene was observed in 7 isolates, and this result did not correlate with that obtained in hemagglutination assay. All the isolates were able to grow in iron-limiting conditions, showing that A. baumannii produces some type of siderophore. However, the genes iutA and fyuA, from iron uptake system of E. coli and Yersinia sp., respectively, were not present in the isolates, suggesting the presence of a different type of siderophore. The fimbriae of A. baumannii strains that mediates the adherence are possibly mannose-resistant, even though the mechanism of adherence to human epithelial cells still remains to be elucidated.

Detection of the cytolethal distending toxin locus cdtB among diarrheagenic Escherichia coli isolates from humans in Iran

Cytolethal distending toxin (CDT) represents an emerging family of newly described bacterial products that are produced by a number of pathogens. Genes encoding this toxin were identified as a cluster of three adjacent genes, cdt-A, cdt-B and cdt-C. Five cdt genetic variants, designated cdt-I, cdt-II, cdt-III, cdt-IV and cdt-V, have been identified so far. To determine the presence of cdt genes among Escherichia coli isolates, a PCR assay was employed. Using multiplex primers designed for detection of E. coli cdt genes, PCR analysis indicated the presence of cdt genes in 37.5% of these isolates. While specific primers were located in the cdt-B locus for detection of cdt-I, cdt-II, cdt-III and cdt-IV, in multiplex PCR positive isolates indicated that a cdt-I-like gene was present in 45.3% of these isolates. However, in 52% of the isolates, the cdt-III-like gene could be detected. It should be mentioned that in 30.8% of these isolates, cdt-II and -III were detected simultaneously. In 2.6% of the isolates, the cdt-IV gene was present. The cnf-1 gene was detected in 29.4% of strains carrying the cdt-I gene; however, the cnf-2 gene was detected only in 23.1% of the cdt-III-like strains. Furthermore, the data obtained by PCR analysis indicated the presence of cdt-like genes among our E. coli isolates, although in the CHO cell assay, all isolates showed a cytopathic effect characteristic of CDT.

Characterization of hemolytic Escherichia coli strains in ferrets: recognition of candidate virulence factor CNF1

Diseases associated with Escherichia coli infection are the subject of renewed interest due to emerging conditions such as hemolytic uremia syndrome. A collection of 15 strains of beta-hemolytic E. coli was isolated from diarrheic feces and diseased tissues of ferrets. All 15 strains were positive in specific PCR assays for the presence of hlyA, pap1, and cnf1. Seven of the cnf1-positive isolates were tested and shown to have a cytopathic effect on HeLa cell monolayers. The pathogenesis of these strains warrants future study.

Detection and isolation of Escherichia coli with a coding gene for enteroaggregative Escherichia coli heat-stable enterotoxin 1 from food and comparison with fecal isolates

Enteroaggregative Escherichia coli heat-stable enterotoxin 1 (EAST1) was originally regarded as a putative enterotoxin of enteroaggregative Escherichia coli. Although its etiological role has not yet been elucidated, it has been epidemiologically suggested that some strains of E. coli possessing EAST1-coding gene (astA) but no other identifiable pathogenic properties comprise a new group of diarrhea-associated E. coli (EAST1EC). However, the source of the organisms and their prevalence in foods are still obscure. In this study, methods for detection of the organisms in foods heavily contaminated with coliforms were evaluated and properties of the isolated strains were compared with those of fecal strains. Four enrichment methods (brilliant green lactose bile broth, E. coli, lauryl tryptose broth, and a combination of brain heart infusion broth and tryptone phosphate broth) were evaluated through inspection of 115 samples. PCR showed positive results in 26 samples after enrichment with a combination of brain heart infusion broth and tryptone phosphate broth, and EAST1EC was successfully isolated from 18 samples. Fifteen samples showed a positive reaction in the PCR test after enrichment by the other methods, and the organisms were isolated from only 10 specimens. The highest prevalence of EAST1EC was found in animal products (16 of 54, 29.6%); the organism was rarely found in foods of plant origin (2 of 45, 4.4%) or fishery products (1 of 16, 6.3%). Although EAST1EC is unexpectedly common in animal products, its potential as a human pathogen remains uncertain because the possession of some virulence properties differs significantly between strains from fecal specimens and those from foods. Some food isolates, however, possess the same characteristics as diarrheal isolates do. It is necessary to clarify the pathogenicity of EAST1EC and the significance of food as a source of infection.

Detection of virulence factors in alpha-haemolytic Escherichia coli strains isolated from various clinical materials

In total, 201 alpha-haemolytic Escherichia coli isolates from various clinical materials (urine samples and vaginal and rectal swabs) were examined by PCR for the presence of genes for the virulence factors alpha-haemolysin (hly), cytotoxic necrotising factor type 1 (cnf1), P-fimbriae (pap), S/F1C-fimbriae (sfa/foc), aerobactin (aer) and afimbrial adhesin (afaI). Among vaginal isolates, 96% were positive for cnf1, compared with 80% of urine strains (p 0.02) and 63% of rectal strains (p 0.0001). Similarly, sfa/foc-specific DNA sequences were found in 97% of vaginal isolates compared with 75% of rectal strains (p 0.004). The afa1 and aer genes were associated more with rectal alpha-haemolytic E. coli strains than with extra-intestinal isolates. The results suggested that CNF1 and/or S/F1C-fimbriae contribute to colonisation and persistence of alpha-haemolytic E. coli strains in the vaginal environment.

Enteroaggregative and cell-detachingEscherichia coli strains among polish children with and without diarrhea

To determine the association of enteroaggregative (EAEC) and cell-detaching (CDEC) Escherichia coli with diarrhea of unknown origin among children from Wrocław (Poland), E. coli strains isolated from stool specimens of children with diarrhea were examined for mannose-resistant adherence to HEp-2 cells. EAEC were isolated from 10 of 39 (26%) children examined with diarrhea and 4 of 20 (20%) age-matched controls. CDEC were present in 14 (36%) cases of diarrhea and 7 (35%) healthy subjects. Cell-detaching activity was distinctly associated with hemolysin production. Among hemolytic CDEC strains cytotoxic necrotizing factor 1 (CNF1) synthesis prevailed among isolates obtained from cases of diarrhea (57%) in comparison with isolates obtained from healthy controls (14.3%). Although neither EAEC nor CDEC E. coli strains were associated with diarrhea of children in this setting, there were differences among EAEC and CDEC strains isolated from children with and without diarrhea.

Virulence-associated genes in Escherichia coli isolates from poultry with colibacillosis

Avian pathogenic Escherichia coli, the causative agent of colibacillosis, harbors several putative virulence genes. In this study we examined by polymerase chain reaction (PCR) the presence of 16 of those genes in 200 colibacillosis isolates from our region. The seven virulence genes iutA, iss, cvaC, tsh, papC, papG and felA were detected significantly more often amongst colibacillosis isolates than in fecal isolates from healthy birds, thereby confirming their worldwide occurrence and possible pathogenic role in colibacillosis. However, several of those genes were not detected in many colibacillosis isolates, and none of them were detected in 27.5% of those isolates, which suggests that variants of those genes and yet undetected virulence factors should be searched for.

Virulence markers of enteroaggregative Escherichia coli isolated from children and adults with diarrhea in Brasília, Brazil

Escherichia coli strains isolated from sporadic cases of acute diarrhea in children and adults and from children without diarrhea were investigated for the presence of the pAA plasmid. Strains harboring the pAA plasmid were isolated at similar frequencies from children with (19.6%) and without (10.8%) diarrhea and from adults with diarrhea (11.8%). The genotypic and phenotypic virulence markers of these strains were further analyzed. Most of the strains were positive for EAST1 (73%), and this toxin was detected significantly more frequently in strains from children with diarrhea than in strains from adults with diarrhea (P < 0.05). Likewise, pic sequences were detected significantly more frequently in strains from children with diarrhea than in strains from adults with diarrhea (P < 0.005) and controls (P < 0.025). Furthermore, the association of pAA positivity (pAA(+)) and pic positivity (pic(+)) was more frequently found for strains from children with diarrhea than for strains from controls, indicating that pAA(+) pic(+) strains may represent a subset of pAA(+) strains associated with disease in children. Most of the strains (82.5%) adhered to cells presenting the typical aggregative pattern. The frequency of occurrence of enteropathogenic E. coli (EPEC) serogroups in the strains from children with diarrhea was very high (56%), while none of the strains from adults with diarrhea belonged to EPEC serogroups. Extraintestinal virulence markers were very commonly found in strains from adults with diarrhea. The frequencies of occurrence of the adhesins AFA and SFA were significantly higher in strains from adults with diarrhea than in strains from children with diarrhea. More than one extraintestinal virulence marker was found in 58% of the strains from adults with diarrhea but in only 7.7% of the strains from children with diarrhea. Our results show that pAA(+) strains isolated from children and adults with diarrhea present very different profiles when enteroaggregative E. coli virulence markers, serotypes, and extraintestinal virulence markers are considered.

Biological activity of Serratia marcescens cytotoxin

Serratia marcescens cytotoxin was purified to homogeneity by ion-exchange chromatography on a DEAE Sepharose Fast Flow column, followed by gel filtration chromatography on a Sephadex G100 column. The molecular mass of the cytotoxin was estimated to be about 50 kDa. Some biological properties of the cytotoxin were analyzed and compared with well-characterized toxins, such as VT1, VT2 and CNF from Escherichia coli and hemolysin produced by S. marcescens. The sensitivity of the cell lines CHO, HeLa, HEp-2, Vero, BHK-21, MA 104 and J774 to the cytotoxin was determined by the cell viability assay using neutral red. CHO and HEp-2 were highly sensitive, with massive cellular death after 1 h of treatment, followed by BHK-21, HeLa, Vero and J774 cells, while MA 104 was insensitive to the toxin. Cytotoxin induced morphological changes such as cell rounding with cytoplasmic retraction and nuclear compactation which were evident 15 min after the addition of cytotoxin. The cytotoxic assays show that 15 min of treatment with the cytotoxin induced irreversible intoxication of the cells, determined by loss of cell viability. Concentrations of 2 CD50 (0.56 g/ml) of purified cytotoxin did not present any hemolytic activity, showing that the cytotoxin is distinct from S. marcescens hemolysin. Antisera prepared against S. marcescens cytotoxin did not neutralize the cytotoxic activity of VT1, VT2 or CNF toxin, indicating that these toxins do not share antigenic determinants with cytotoxin. Moreover, we did not detect gene sequences for any of these toxins in S. marcescens by PCR assay. These results suggest that S. marcescens cytotoxin is not related to any of these toxins from E. coli.

Occurrence and genetic association of selected virulence factors in clinical Escherichia coli isolates

Occurrence of cnf1+ E. coli pathogenic strains among extraintestinal E. coli isolates was evaluated to explain an impact of cytotoxic necrotizing factor type 1 (CNF1) in human infections. A total of 120 E. coli isolates were characterized for presence of virulence factors cnf1- and pap--specific sequences by PCR, and the production of alpha-hemolysin using blood agar-plate test. Different association patterns among the detected virulence factors were obtained by comparison of various groups of clinical E. coli isolates. These differences probably reflect a potential impact of CNF1 in the colonization of vaginal environment.

Microbiological comparative study of isolates of Edwardsiella tarda isolated in different countries from fish and humans

It is difficult to use tissue culture assays to investigate adherence and other properties of Edwardsiella tarda because the organism is invasive and produces a potent hemolysin. We therefore relied on polymerase chain reaction (PCR) to determine the occurrence of genes for enterotoxins (LT-I, EAST-1), Shiga toxin (Stx-1, Stx-2), cytotoxic necrotizing factors (CNF-1, CNF-2), aerobactin, invasion plasmid of enteroinvasive Escherichia coli, EPEC adherence factor (EAF), intimin (Eae), enterohemolysin (EntHly) and hemolysin (Hly) in 53 isolates of E. tarda from humans and fish from several countries. All isolates were negative for all genes investigated by PCR. Adhesion to and invasion of HeLa cells were determined by using the unusually short incubation time of 1h or 30 min. All isolates adhered and invaded in these tests. Finally, a random amplified polymorphic DNA (RAPD) test distinguished, with a few exceptions, isolates of human and fish origin.

Serobiotypes and virulence genes of Escherichia coli strains isolated from diarrheic and healthy rabbits in Brazil

A total of 178 Escherichia coli isolates from diarrheic and healthy rabbits in the São Paulo State (Brazil) were serobiotyped and investigated by PCR for the presence of virulence genes. Among the 90 (50.6%) isolates which possessed the eae gene, 74 were from diarrheic animals and all but one encoded intimin beta. Sixty five (72.2%) of the eae+ isolates had insertion of the locus of enterocyte effacement locus in the pheU locus, 11 (12.2%) in the selC and 14 (15.6%) did not insert in either of these loci. All isolates were negative for genes of the E. coli enterotoxins, Stx1, Stx2, CNF1, CNF2 and EHEC hemolysin. The O132:H2 serotype was dominant, being present in 63 isolates (70%) of the 90 eae+ isolates, and 57 of the 63 isolates of this serotype belonged to biotype 30. PCR detected the gene for AF/R2 fimbriae in 75 (83.3%) of the 90 eae+ isolates. Adherence to HeLa cells was best detected following 6h incubation and a positive fluorescence actin staining (FAS) test was given by 52 isolates. These data show that isolates of E. coli associated with diarrhea in rabbits in Brazil possess the genotype and phenotype typically associated with rabbit enteropathogenic E. coli (EPEC). We conclude that EPEC that possess the eae gene are a common cause of diarrhea in Brazilian rabbit farms and that the pathogenic eae+ AF/R2+ isolates of O132:H2:B30 serobiotype are especially predominant.

Verotoxin-producing Escherichia coli (VTEC), enteropathogenic E. coli (EPEC) and necrotoxigenic E. coli (NTEC) isolated from healthy cattle in Spain

AIMS

To determine the prevalence and characteristics of verotoxigenic Escherichia coli (VTEC), enteropathogenic E. coli (EPEC) and necrotoxigenic E. coli (NTEC) in healthy cattle.

METHODS AND RESULTS

Faecal samples from 412 healthy cattle were screened for the presence of VTEC, EPEC and NTEC. Four isolates from each sample were studied. VTEC, EPEC and NTEC were isolated in 8.7%, 8.2% and 9.9% of the animals, respectively. VTEC and NTEC were isolated more frequently from calves and heifers than from adults. Seventy (4.2%), 69 (4.2%) and 74 (4.5%) of the 1648 E. coli isolates were VTEC, EPEC and NTEC, respectively. Seventeen (24.3%) of the VTEC strains were eae-positive. Thirty-six (51.4%) of VTEC strains belonged to E. coli serogroups associated with haemorrhagic colitis and haemolytic uraemic syndrome in humans. The serogroups most prevalent among the EPEC strains were O10, O26, O71, O145 and O156.

CONCLUSIONS

Healthy cattle are a reservoir of VTEC, EPEC and NTEC.

SIGNIFICANCE AND IMPACT OF THE STUDY

Although most of the VTEC strains were eae-negative, a high percentage of VTEC strains belonged to serogroups associated with severe disease in humans.

PCR for detection of cdt-III and the relative frequencies of cytolethal distending toxin variant-producing Escherichia coli isolates from humans and cattle

A PCR assay that uses primers whose sequences were obtained from the published sequence of the cdt-III gene was developed to determine the frequencies of the cdt-I, cdt-II, and cdt-III genes in Escherichia coli isolates from humans and animals. E. coli isolates producing cytolethal distending toxin (CDT) were infrequently detected. The cdt-I gene was preferentially detected in strains with the cnf1 gene, while the cdt-III gene was found in strains carrying the cnf2 gene. The cdt-III genotype was more prevalent in animal isolates, while the cdt-I and cdt-II genotypes were more evident in human isolates. The presence of further cdt gene variants was indicated by the presence of toxin activity in cell culture in the absence of PCR amplification of the cdt-I, cdt-II, or cdt-III gene.

Characterization of necrotoxigenic Escherichia coli (NTEC) strains isolated from healthy calves in Poland

Faecal samples from 132 healthy, 4-8-week-old calves from four different farms were examined for necrotoxigenic Escherichia coli (NTEC) producing the cytotoxic necrotizing factors type 1 (CNF1) and type 2 (CNF2). CNF2 genes were detected by polymerase chain reaction in 24 (6.1%) of the 396 E. coli strains tested; these strains were found in 18 (13.6%) calves used in the study. None of the 396 E. coli isolates examined possessed the gene encoding CNF1. Overall, 28.8% of E. coli examined expressed the F17 fimbrial antigen. A strong association between CNF2 toxin and F17 fimbriae was found (62.5% of CNF2-positive strains were F17-positive). Moreover, six out of 24 NTEC strains had the Stx1 or the Stx2 shiga toxin genes, and three additional isolates possessed the eae genetic marker of the intimin protein.

Biological and genetic characteristics of uropathogenic Escherichia coli strains

The aim of the present study was to determine biological characteristics such as expression of fimbriae, Congo red binding, production of hemolysin and aerobactin, adhesion to HeLa and uroepithelial cells and invasion of HeLa cells by Escherichia coli isolates obtained from patients showing clinical signs of urinary tract infection (UTI). Also, the presence of genes (apa, afa, spa) for fimbria expression and cytotoxic necrotizing factors (CNF1, CNF2) was assayed using specific primers in PCR. The data obtained were compared with the clonal relationships obtained by analysis of multilocus enzyme electrophoresis (MLEE), restriction fragment length polymorphism (RFLP) of the rDNA (ribotyping) and enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR). All isolates but one presented a combination of at least two of the characteristics studied, a fact suggesting the presence of pathogenicity islands (PAIs). Diffuse adherence type to HeLa cells was observed to occur in most of the strains, but adhesion to uroepithelial cells seems to be a more reliable test to verify pathogenicity. Although four strains seemed to be able to invade HeLa cells when assayed by light microscopy, electron microscopy studies demonstrated that these strains were not invasive. MLEE, RFLP and ERIC-PCR were able to group the isolates differently into main clusters that were not correlated with the presence of pathogenic traits.

Characterization of shiga toxin-producing Escherichia coli strains isolated from calves in Poland

Fecal samples from 67 3-5-months-old calves with diarrhea were screened for the presence of shiga toxin-producing Escherichia coli (STEC). Several accessory virulence factors genes were also tested. Among 192 E. coli isolates tested, 15 (7.6%) were found to harbour the shiga toxin 1 or 2 (stx1 or stx2) genes. The stx2-carrying samples were further subtyped by PCR for the stx2c, stx2d, and stx2e toxin variants. It was shown that stx2-positive bacteria mainly possessed the stx2c shiga toxin type gene. The enterohemolysin (hlyA) and intimin (eae) genes were found in seven (46.7%) STEC strains whereas the cytotoxic necrotizin factor 1 and 2 or the P fimbrial genes were detected in two isolates only. This study confirmed that calves are a reservoir of STEC strains (with all pathogenicity genes) that may be virulent for humans.

Characterization of intestinal cnf1+ Escherichia coli from weaned pigs

Escherichia coli isolated from 204 cases of porcine postweaning diarrhoea were tested by PCR for the genes of cytotoxic necrotic factors (CNF) and of cytolethal dystending toxin (CDT). Selected strains were also examined by PCR for the presence of papC-, sfa-, f17-, f18-, and afa-specific sequences encoding P, S, F17, F18 fimbriae and afimbrial adhesins. A 5.9% (12/204) of the strains had cnf1 gene, and two of them had cdt gene as well. Further six cdt+ strains were detected which were cnf-negative. Most of the cnf1+ strains belonged to serogroups O2, O6, O8, O54 characteristic of necrotoxic E. coli (NTEC) of humans. All the cnf1+ strains possessed the genes for P or S fimbriae or both, but were negative for F4, F17, or F18 or afimbrial adhesins. Results suggest that these enteric isolates may have entero- and/or uropathogenic significance in weaned pigs, and may have zoonotic potential for humans.

Effect of human immunodeficiency virus infection on episodes of diarrhea among children in South Africa

BACKGROUND

Infection with HIV is increasing among children in South Africa. Diarrhea is a common cause of morbidity and mortality in Africa, and some studies have shown that HIV-infected children have episodes of severe diarrhea with higher mortality than HIV-uninfected children.

OBJECTIVES

To compare the severity, pathogens and outcome of diarrhea in HIV-infected and uninfected children.

METHODS

We studied 181 children ages 3 months to 4 years admitted for gastroenteritis to the Chris Hani Baragwanath Hospital in Soweto, South Africa. Demographic details of the children were recorded, as were the details of the episode of diarrhea. Stools specimens were collected and sent for microbiologic evaluation. The clinical course of the child's admission was recorded. Children were diagnosed as being infected with HIV if they tested positive by HIV enzyme-linked immunosorbent assay (ELISA) and were >15 months of age, or if they were ELISA-positive, were < 15 months of age and had clinical signs of HIV infection.

RESULTS

Of the 176 children with an HIV ELISA result, 31 (17.6%) were classified as HIV-infected. More HIV-infected children were malnourished (80.6% vs. 39.5%, P < 0.001) and more likely to have had prolonged diarrhea (16.1% vs. 5.9%, P = 0.07) compared with HIV-uninfected children. HIV-infected children had a higher rate of a codiagnosis of pneumonia (43.3% vs. 9.2%, P < 0.0001) and were more likely to require a hospital stay of >4 days (prevalence odds ratio, 5.11; 95% confidence interval, CI 1.49 to 17.52). There were no significant differences in stool pathogens or in the level of dehydration on admission between the HIV-infected and uninfected children.

CONCLUSION

HIV-infected children have the same spectrum of enteric pathogens as uninfected children but require more attention because of malnutrition and comorbidity.

In vitro susceptibility of Escherichia coli strains isolated from diarrhoeic dairy calves to 15 antimicrobial agents

The in vitro activities of 15 antimicrobial agents against 195 strains of Escherichia coli isolated from dairy calves affected by neonatal diarrhoea were determined. Of these strains 137 produced one or more potential virulence factors (F5, F41, F17, cytotoxic necrotizing factor, verotoxin and the eae gene), but the remaining 58 strains did not produce any of these factors. The overall percentage of resistant strains to streptomycin, tylosin and tetracycline was very high (above 65%). A high level of resistance (from 23 to 50%) to ampicillin, neomycin, kanamycin, spectinomycin, chloramphenicol, sulphadimethoxine and trimethoprim was also detected. The E. coli strains were very susceptible (89-95%) to apramycin and gentamicin and highly susceptible (99-100%) to polymyxin B, florfenicol and nitrofurazone. Some significant differences (P < 0.05) in the frequencies of resistance to some of the antimicrobials tested and in the rates of multi-drug resistance among the strains producing potential virulence factors and non-fimbriated, non-toxigenic, eae-negative strains were found. Most of the strains showed multi-resistance: 76.9% of the isolates were resistant to at least two antibiotics, 67.7% were resistant to at least four antibiotics and 50.3% were resistant to at least six antibiotics.

Comparison of necrotoxigenic Escherichia coli isolates from farm animals and from humans

Necrotoxigenic Escherichia coli (NTEC) isolated from animals and humans can belong to the same serogroups/types and produce or carry the genes coding for fimbrial and afimbrial adhesins of the same family, P, S, F17, and/or AFA, raising the question of a potential zoonotic source of human infection. The main purpose of this study was to compare 239 NTEC1 strains (45 from cattle, 65 from humans and 129 from piglets) and 98 NTEC2 strains from cattle, using a uniform and standardized typing scheme. The O serogroups and the biotypes recognized amongst NTEC1 and NTEC2 strains were quite varied, although some were more frequently observed (serogroups O2, O4, O6, O8, O18, O78, and O83 and biotypes 1, 2, 5, 6, and 9). Hybridization, results with gene probes for the P family (PAP probe), S family (SFA probe), AFA family (AFA probe), F17 family (F17 probe) of fimbrial and afimbrial adhesins, could differentiate most NTEC1 strains, which are PAP-, SFA- and/or AFA-positive, from NTEC2 strains, which are mainly F17- and/or AFA-positive, but were of no help in differentiating between NTEC1 strains from cattle, humans, and piglets. All but seven (98%) NTEC1 and NTEC2 strains were serum resistant, 199 (59%) produced an aerobactin, and colicin (I, V, or unidentified) was produced by 22-34% of them. On the other hand, more than 90% of the NTEC1 strains were haemolytic on sheep blood agar compared with only 40% of the NTEC2 strains. Production of a classical haemolysin, active on sheep erythrocytes, and hybridization with the PAP probe were associated in a majority of NTEC1 strains (63-81%), but very rarely in NTEC2 strains (3%). Production of enterohaemolysin and hybridization with the PAP probe were much less frequently associated in NTEC strains (1-9%). It was thus possible neither to completely differentiate NTEC1 strains from cattle, humans, and pigs, nor to define a signature for the NTEC strains. Necrotoxigenic E. coli must still be identified on the basis of the production of the Cytotoxic Necrotizing Factors 1 or 2 (or of their encoding genes) and complete differentiation of NTEC1 strains from cattle, humans, and piglets, use additionnal methods.

Prevalence and characteristics of necrotoxigenic Escherichia coli (NTEC) strains isolated from diarrhoeic dairy calves

Fecal samples from 246, 1-90-days old diarrhoeic dairy calves in 72 herds were screened for the presence of cytotoxic necrotizing factors (CNF)-producing Escherichia coli (NTEC). NTEC were detected by tissue culture assays and PCR in 39 (15.8%) of the diarrheic calves, and the majority of these animals (34 of 39, ca. 87.2%) were infected by NTEC producing CNF2. Calves were grouped according to their age (1-7 days, 8-14 days, 15-21 days, 22-30 days and 31-90 days) and analyses of prevalence were done by the Mantel-Haenzsel chi2-test for trend. A significant age-associated increase in the prevalence of NTEC producing CNF2 (p<0.0001) was found. Eighty-one (8.4%) of the 958 E. coli isolates from the 246 diarrheic calves were positive for CNF in the tissue culture assays. These strains were analyzed by PCR and this technique showed that three (3.7%) strains were CNF1-positive and 75 (92.6%) were CNF2-positive. Moreover, three of the strains positive in the tissue culture assays were negative by PCR. These strains were subsequently assayed in several biological tests (rabbit skin test, mouse intraperitoneal test and mouse footpad test) which showed that they were really NTEC, probably producing CNF2, but with some different properties to classical strains producing CNF2. NTEC strains producing CNF2 belonged to different serogroups (O2, O7, O9, O14, O15, O41, O43, O45, O55, O76, O86, O88, O109, O115, O123, O128, O153 and O159) than strains producing CNF1 (O11 and O32) or PCR-negative strains (O111). Moreover, a strong association between CNF2 and F17 fimbriae was found (78.6% of CNF2-positive strains were F17-positive, whereas only 22.9% of CNF2-negative strains were F17-positive).

Characterization of nonenterotoxigenic Escherichia coli strains producing F17 fimbriae isolated from diarrheic lambs and goat kids

Forty-five ovine and caprine nonenterotoxigenic Escherichia coli strains producing F17-related fimbriae were characterized with respect to the fimbrial structural subunit and adhesin subtypes produced. In addition, several characteristics related to the virulence of strains producing F17 fimbriae were studied. Most of the strains (73%) possessed the f17cA structural subunit gene, whereas the f17aA and f17dA genes were detected only on three (6%) and two (4%) strains, respectively. The f17bA gene was not detected. All but one of these strains possessed the f17G genes of the adhesin subfamily II. The only strain having the f17G gene of subfamily I possessed the structural subunit gene f17dA. Sequencing of the f17A and f17G genes of four selected strains confirmed the association of f17cA and f17dA structural subunit genes with the f17G genes of the adhesin subfamily II. These results indicated that adhesins of the subfamily II are prominent among ovine and caprine isolates and that they are indistinctly associated with the F17 structural subunit subtypes on these field strains. CS31A- and CNF2-related genes were not detected. Most of the strains adhered in vitro to ovine intestinal brush borders (36 of 45) and agglutinated the erythrocytes of different species in the presence of D-mannose (39 of 45). F17-positive strains produced colicin V (57%) and were resistant to the bactericidal effect of serum (91%) in significantly higher percentages than F17-negative strains (34% produced colicin V, and 66% were serum resistant). Thus, most of the studied ovine and caprine strains showed phenotypic characteristics of septicemic strains.

In vitro activities of cephalosporins and quinolones against Escherichia coli strains isolated from diarrheic dairy calves

The in vitro activities of several cephalosporins and quinolones against 195 strains of Escherichia coli isolated from diary calves affected by neonatal diarrhea were determined. One hundred thirty-seven of these strains produced one or more potential virulence factors (F5, F41, F17, cytotoxic necrotizing factor, verotoxin, and the eae gene), but the remaining 58 strains did not produce any of these factors. From 11 to 18% of the E. coli strains were resistant to cephalothin, nalidixic acid, enoxacin, and enrofloxacin. However, cefuroxime, cefotaxime, and cefquinome were highly effective against the E. coli isolates tested. Some significant differences (P < 0.05) in resistance to quinolones between the strains producing potential virulence factors and nonfimbriated, nontoxigenic, eae-negative strains were found. Thus, eae-positive, necrotoxigenic, and verotoxigenic (except for nalidixic acid) E. coli strains were significantly more sensitive to nalidixic acid, enoxacin, and enrofloxacin than nonfimbriated, nontoxigenic, eae-negative strains. Moreover, eae-positive strains were significantly more sensitive to enoxacin and enrofloxacin than F5-positive strains. Thus, the result of this study suggest that the bovine E. coli strains that produce some potential virulence factors are more sensitive to quinolones than those that do not express these factors.

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).