Characterization of Shiga toxin-producing Escherichia coli strains isolated from human patients in Germany over a 3-year period

Simplex and multiplex real-time PCR assays for the detection of flagellar (H-antigen) fliC alleles and intimin (eae) variants associated with enterohaemorrhagic Escherichia coli (EHEC) serotypes O26:H11, O103:H2, O111:H8, O145:H28 and O157:H7

AIMS

To develop real-time PCR assays targeting genes encoding the flagellar antigens (fliC) and intimin subtypes (eae) associated with the five most clinically important serotypes of enterohaemorrhagic Escherichia coli (EHEC), i.e. O26:H11, O103:H2, O111:H8, O145:H28 and O157:H7.

METHODS AND RESULTS

  Primers and probes specific to fliC(H2) , fliC(H7) , fliC(H8) , fliC(H11) , fliC(H28) , eae-β1, eae-γ1, eae-ε and eae-θ were combined in simplex and multiplex 5'-nuclease PCR assays. The specificity of the assays was assessed on 201 bacterial strains and the sensitivity determined on serially diluted EHEC genomes. The developed PCR assays were found to be highly specific and detected as few as five EHEC genome equivalents per reaction. Furthermore, it was possible to detect the five major EHEC serotypes in cheese samples inoculated at concentration levels of ≤5CFU per 25g after overnight enrichment using the PCR assays.

CONCLUSIONS

The PCR assays developed here were found to be sensitive and specific for the reliable detection of genes encoding the flagellar antigens and intimin variants belonging to the five most clinically relevant EHEC serotypes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Application of real-time PCR assays should improve the identification of foods contaminated by EHEC and facilitate the molecular typing of these organisms.

Distribution and phylogeny of immunoglobulin-binding protein G in Shiga toxin-producing Escherichia coli and its association with adherence phenotypes

eibG in Shiga toxin-producing Escherichia coli (STEC) O91 encodes a protein (EibG) which binds human immunoglobulins G and A and contributes to bacterial chain-like adherence to human epithelial cells. We investigated the prevalence of eibG among STEC, the phylogeny of eibG, and eibG allelic variations and their impact on the adherence phenotype. eibG was found in 15.0% of 240 eae-negative STEC strains but in none of 157 eae-positive STEC strains. The 36 eibG-positive STEC strains belonged to 14 serotypes and to eight multilocus sequence types (STs), with serotype O91:H14/H(-) and ST33 being the most common. Sequences of the complete eibG gene (1,527 bp in size) from eibG-positive STEC resulted in 21 different alleles with 88.11% to 100% identity to the previously reported eibG sequence; they clustered into three eibG subtypes (eibG-alpha, eibG-beta, and eibG-gamma). Strains expressing EibG-alpha and EibG-beta displayed a mostly typical chain-like adherence pattern (CLAP), with formation of long chains on both human and bovine intestinal epithelial cells, whereas strains with EibG-gamma adhered in short chains, a pattern we termed atypical CLAP. The same adherence phenotypes were displayed by E. coli BL21(DE3) clones containing the respective eibG-alpha, eibG-beta, and eibG-gamma subtypes. We propose two possible evolutionary scenarios for eibG in STEC: a clonal development of eibG in strains with the same phylogenetic background or horizontal transfer of eibG between phylogenetically unrelated STEC strains.

Characterization of a gne::IS629 O rough:H7 Escherichia coli strain from a hemorrhagic colitis patient

Shiga-toxigenic Escherichia coli strains that are O rough:H7 due to gne::IS629 were thought to be rare and to have unknown pathogenic potential. Recently, an O rough:H7 strain caused by gne::IS629 was isolated from a hemorrhagic colitis patient, suggesting that these strains are pathogenic and may not be as rare as anticipated.

Characteristics of shiga toxin-producing Escherichia coli isolated from Swiss raw milk cheese within a 3-year monitoring program

Food is an important vehicle for transmission of Shiga toxin-producing Escherichia coli (STEC). To assess the potential public health impact of STEC in Swiss raw milk cheese produced from cow's, goat's, and ewe's milk, 1,422 samples from semihard or hard cheese and 80 samples from soft cheese were examined for STEC, and isolated strains were further characterized. By PCR, STEC was detected after enrichment in 5.7% of the 1,502 raw milk cheese samples collected at the producer level. STEC-positive samples comprised 76 semihard, 8 soft, and 1 hard cheese. By colony hybridization, 29 STEC strains were isolated from 24 semihard and 5 soft cheeses. Thirteen of the 24 strains typeable with O antisera belonged to the serogroups O2, O22, and O91. More than half (58.6%) of the 29 strains belonged to O:H serotypes previously isolated from humans, and STEC O22:H8, O91:H10, O91:H21, and O174:H21 have also been identified as agents of hemolytic uremic syndrome. Typing of Shiga toxin genes showed that stx(1) was only found in 2 strains, whereas 27 strains carried genes encoding for the Stx(2) group, mainly stx(2) and stx(2vh-a/b). Production of Stx(2) and Stx(2vh-a/b) subtypes might be an indicator for a severe outcome in patients. Nine strains harbored hlyA (enterohemorrhagic E. coli hemolysin), whereas none tested positive for eae (intimin). Consequently, semihard and hard raw milk cheese may be a potential source of STEC, and a notable proportion of the isolated non-O157 STEC strains belonged to serotypes or harbored Shiga toxin gene variants associated with human infections.

Evaluation of multiple-locus variable number of tandem-repeats analysis (MLVA) as a method for identification of clonal groups among enteropathogenic, enterohaemorrhagic and avirulent Escherichia coli O26 strains

A published multiple-locus variable number of tandem-repeats analysis (MLVA) scheme was compared with pulsed-field gel electrophoresis (PFGE) for genotyping of 62 Escherichia coli O26 strains from humans, animals and food. The strains were isolated between 1947 and 2006 in eight countries on three continents and divided into 23 enterohaemorrhagic E. coli (EHEC), 33 enteropathogenic E. coli (EPEC), one enterotoxigenic E. coli (ETEC) and five avirulent strains. ETEC and avirulent E. coli serotyped as O26:H32. EHEC and EPEC O26 strains shared flagellar type H11 and the eae-beta gene, and divided into two clonal lineages by their arcA gene sequence and fermentation of rhamnose and dulcitol. The rhamnose/dulcitol-nonfermenting (RDF-), 'arcA allele 1' type comprised 22 EHEC and 15 EPEC strains. The rhamnose/dulcitol-fermenting (RDF+), 'arcA allele 2' type encompassed 17 EPEC and one EHEC strain. PFGE typing of the 62 O26 strains revealed 54 distinct patterns, whereas 29 profiles were obtained by MLVA. Like PFGE, MLVA divided RDF- and RDF+ O26:[H11] strains into two distinct clusters of related strains. The O26:H32 strains formed a separate PFGE cluster and two clusters by MLVA. MLVA was found as suitable, but more rapid and easier to standardize than PFGE for identifying genetically related E. coli O26 strains.

A C-terminal cationic fragment derived from an arginine-rich peptide exhibits in vitro antibacterial and anti-plasmodial activities governed by its secondary structure properties

The differential in vitro antimicrobial activity of a 12-residue-long arginine-rich peptide derived from protamine was examined against bacterial and parasite microbes. A design of discrete peptide fragments based on the thermolysin-digestion map allowed us to propose three peptide fragments to be further assessed regarding their biological and secondary structural properties. Peptide structure allowed designing three arginine-rich fragments. All peptide fragments were assessed regarding their antimicrobial activity against Gram-positive and Gram-negative bacteria and a human malaria strain. Qualitative and quantitative assays carried out for determining all peptides' antibacterial activity at different concentration levels included radial diffusion and a time-controlled technique. Tests demonstrated that all assessed molecules inhibited invasion of Plasmodium falciparum parasites to human red blood cells. Cytolytic activity of the parent protamine peptide was completely abolished by strategically fragmenting its aminoacid sequence. Remarkably, the cationic C-fragment exhibited stronger biological activity than its parent peptide. Interestingly, the peptide fragment denoted as 2077 displays a typical alpha-helix profile according to its CD spectrum. The results support proposing the protamine C-terminal fragment as a potential new antimicrobial peptide.

Low-density macroarray targeting non-locus of enterocyte effacement effectors (nle genes) and major virulence factors of Shiga toxin-producing Escherichia coli (STEC): a new approach for molecular risk assessment of STEC isolates

Rapid and specific detection of Shiga toxin-producing Escherichia coli (STEC) strains with a high level of virulence for humans has become a priority for public health authorities. This study reports on the development of a low-density macroarray for simultaneously testing the genes stx1, stx2, eae, and ehxA and six different nle genes issued from genomic islands OI-122 (ent, nleB, and nleE) and OI-71 (nleF, nleH1-2, and nleA). Various strains of E. coli isolated from the environment, food, animals, and healthy children have been compared with clinical isolates of various seropathotypes. The eae gene was detected in all enteropathogenic E. coli (EPEC) strains as well as in enterohemorrhagic E. coli (EHEC) strains, except in EHEC O91:H21 and EHEC O113:H21. The gene ehxA was more prevalent in EHEC (90%) than in STEC (42.66%) strains, in which it was unequally distributed. The nle genes were detected only in some EPEC and EHEC strains but with various distributions, showing that nle genes are strain and/or serotype specific, probably reflecting adaptation of the strains to different hosts or environmental niches. One characteristic nle gene distribution in EHEC O157:[H7], O111:[H8], O26:[H11], O103:H25, O118:[H16], O121:[H19], O5:H-, O55:H7, O123:H11, O172:H25, and O165:H25 was ent/espL2, nleB, nleE, nleF, nleH1-2, nleA. (Brackets indicate genotyping of the flic or rfb genes.) A second nle pattern (ent/espL2, nleB, nleE, nleH1-2) was characteristic of EHEC O103:H2, O145:[H28], O45:H2, and O15:H2. The presence of eae, ent/espL2, nleB, nleE, and nleH1-2 genes is a clear signature of STEC strains with high virulence for humans.

Assessment of Shiga toxin-producing Escherichia coli isolates from wildlife meat as potential pathogens for humans

A total of 140 Shiga toxin-producing Escherichia coli (STEC) strains from wildlife meat (deer, wild boar, and hare) isolated in Germany between 1998 and 2006 were characterized with respect to their serotypes and virulence markers associated with human pathogenicity. The strains grouped into 38 serotypes, but eight O groups (21, 146, 128, 113, 22, 88, 6, and 91) and four H types (21, 28, 2, and 8) accounted for 71.4% and 75.7% of all STEC strains from game, respectively. Eighteen of the serotypes, including enterohemorrhagic E. coli (EHEC) O26:[H11] and O103:H2, were previously found to be associated with human illness. Genes linked to high-level virulence for humans (stx(2), stx(2d), and eae) were present in 46 (32.8%) STEC strains from game. Fifty-four STEC isolates from game belonged to serotypes which are frequently found in human patients (O103:H2, O26:H11, O113:H21, O91:H21, O128:H2, O146:H21, and O146:H28). These 54 STEC isolates were compared with 101 STEC isolates belonging to the same serotypes isolated from farm animals, from their food products, and from human patients. Within a given serotype, most STEC strains were similar with respect to their stx genotypes and other virulence attributes, regardless of origin. The 155 STEC strains were analyzed for genetic similarity by XbaI pulsed-field gel electrophoresis. O103:H2, O26:H11, O113:H21, O128:H2, and O146:H28 STEC isolates from game were 85 to 100% similar to STEC isolates of the same strains from human patients. By multilocus sequence typing, game EHEC O103:H2 strains were attributed to a clonal lineage associated with hemorrhagic diseases in humans. The results from our study indicate that game animals represent a reservoir for and a potential source of human pathogenic STEC and EHEC strains.

Identification of enteropathogenic and enterohaemorrhagic Escherichia coli strains by immunoserological detection of intimin

AIMS

To evaluate the sensitivity and specificity of polyclonal and monoclonal antibodies (Mabs) against intimin in the detection of enteropathogenic and enterohaemorrhagic Escherichia coli isolates using immunoblotting.

METHODS AND RESULTS

Polyclonal and Mabs against the intimin-conserved region were raised, and their reactivities were compared in enteropathogenic E. coli (EPEC) and enterohaemorrhagic E. coli (EHEC) isolates using immunoblotting analysis. In comparison with rat antiserum, rabbit anti-intimin IgG-enriched fraction had a stronger recognition pattern to a wide spectrum of intimin types in different EPEC and EHEC serotypes. On the other hand, murine monoclonal IgG2b specific to intimin, with dissociation constant of 1.3x10(-8) mol l(-1), failed in the detection of some of these isolates.

CONCLUSION

All employed antibodies showed 100% specificity, not reacting with any of the eae-negative isolates. The sensitivity range was according to the employed antisera, and 97% for rabbit anti-intimin IgG-enriched fraction, followed by 92% and 78% sensitivity with rat antisera and Mab.

SIGNIFICANCE AND IMPACT OF THE STUDY

The rabbit anti-intimin IgG-enriched fraction in immunoblotting analysis is a useful tool for EPEC and EHEC diagnoses.

Survival and spread of Shiga toxin-producing Escherichia coli in alpine pasture grasslands

AIMS

To determine the fate of Shiga toxin-producing Escherichia coli (STEC) strains defecated onto alpine grassland soils.

METHODS AND RESULTS

During the summers of 2005 and 2006, the field survival of STEC was monitored in cowpats and underlying soils in four different alpine pasture units. A most probable number (MPN)-PCR stx assay was used to enumerate STEC populations. STEC levels ranged between 3.9 and 5.4 log(10) CFU g(-1) in fresh cowpats and slowly decreased until their complete decay (inactivation rates k < 0.04 day(-1)). PFGE typing of STEC strains isolated from faecal and soil samples assessed the persistence of various clonal types for at least 2 months in cowpats and their vertical dispersal down through the soil at a depth up to at least 20 cm. STEC cells counts in soil were always below 2 log(10) CFU g(-1), regardless of the pasture unit investigated. The soil became rapidly free of detectable STEC once the cowpat had decomposed. The eight STEC strains isolated during this study belonged to six distinct serotypes and tested positive for the gene(s) stx2, including the stx2g and stx2 NV206 variants.

CONCLUSIONS

STEC were able to persist in cowpats and disseminate down through the soil but were unable to establish.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides useful information concerning the ecology of STEC in alpine pasture grasslands and may have implications for land and cattle management.

Molecular analysis of virulence profiles and Shiga toxin genes in food-borne Shiga toxin-producing Escherichia coli

In this study, 75 Shiga toxin (Stx)-producing Escherichia coli (STEC) strains originating from foods (n = 73) and drinking water (n = 2) were analyzed for their stx genotype, as well as for further chromosome-, phage-, and plasmid-encoded virulence factors. A broad spectrum of stx genes was detected. Fifty-three strains (70.7%) contained stx(2) or stx(2) variants, including stx(2d), mucus-activatable stx(2d), stx(2e), and stx(2g). Seven strains (9.3%) harbored stx(1) or stx(1c), and 15 strains (20.0%) carried both stx(2) and/or stx(2) variants and stx(1) or stx(1c). Beside stx, the most abundant accessory virulence markers in STEC food isolates were iha (57.3%), ehxA (40.0%), espP (28.0%), and subAB (25.3%). Only four strains were eae positive; three of these belonged to the serogroups O26, O103, and O157 and contained a typical enterohemorrhagic E. coli virulence spectrum. The results of this study show that a number of STEC strains that occur in foods appear to be pathogenic for humans, based on their virulence profiles. Analysis of stx subtypes and detection of additional virulence factors in eae-negative strains may help to better assess the risk of such strains for causing human infection.

Sorbitol-fermenting Shiga toxin-producing Escherichia coli O157 in Austria

Infections with enterohemorrhagic Escherichia coli (EHEC) are the major cause of hemolytic uremic syndrome (HUS), the most common cause of acute renal failure in childhood. Shiga toxins are considered to be the most important virulence factor of EHEC strains. Non-sorbitol-fermenting EHEC O157:H7 is still the most prevalent serotype isolated worldwide; however, sorbitol-fermenting (SF) EHEC O157:H- (H- indicates nonmotility) strains are increasingly reported. Thirteen SF EHEC O157:H- strains (11 of human origin, two from animals) were detected in Austria between 2002 and 2008. Among the 11 human cases, seven suffered from HUS, two from diarrhea and the remaining two were asymptomatic. Seven of the cases were identified in patients living in or visiting (in one case) the province Salzburg, four were in patients from the province Vorarlberg. Three outbreaks with no more than three persons involved were detected, the other four cases occurred sporadically. The pulsed-field gel-electrophoresis banding patterns of the 13 SF EHEC O157:H- isolates were grouped into three distinct clusters (groups 1, 2 and 3). Strains of the three outbreaks were identical (except for one outbreak strain with one band difference) within each outbreak. In comparison, the Bavarian epidemic strain showed a pattern different from all SF O157:H- strains isolated in Austria. For effective detection of SF EHEC O157:H-, screening for Shiga toxins by ELISA and/or Shiga toxin genes by PCR is absolutely necessary; screening on the basis of phenotypic characteristics such as sorbitol-non-fermentation is not sufficient. Typing methods relying solely on investigation of O157 will detect these strains but should nevertheless also be avoided, so that the prevalent non-O157 strains causing HUS are not missed.

Analysis of Escherichia coli isolated from bovine mastitic milk

Mastitis has been recognized for some time as the most costly disease in dairy herds. From February to November 2004, 670 samples of bovine mastitic milk from which 231 Escherichia coli strains were isolated, were collected from two Brazilian states. The strains were screened for the presence of Shiga toxin-producing (stx 1 and stx 2) and intimin (eae) genes. Twenty (8.6%) strains were detected by PCR to harbor the Shiga toxin genes (8 the stx 1 gene, 12 the stx 2 gene and none both of them). Two (0.8%) of the Escherichia coli strains studied were eae positive non Shiga toxin-producing. The strains were also examined for resistance to 12 antimicrobial agents. The predominantly observed resistance was to tetracycline (92.2%), streptomycin (90.4%), nalidixic acid (88.3%), amikacin (86.5%) and cephalothin (84.8%). Multidrug resistance was found among 152 isolates (65.8%).

Intrahost genome alterations in enterohemorrhagic Escherichia coli

Bacterial chromosomes are not fixed molecules; they evolve over the course of infections in human beings. During infection, a variety of strong selective pressures are exerted on the pathogen. The resulting genetic changes that occur in intestinal pathogens might influence clinical outcome and have an impact on diagnosis and epidemiology. Enterohemorrhagic Escherichia coli (EHEC) is a good example of this process. These zoonotic pathogens cause diarrhea, bloody diarrhea, and hemolytic uremic syndrome in human beings, whereas in their natural habitat they mostly are asymptomatic colonizers. Thus, EHEC must be able to quickly adapt from one milieu to another. The greatest challenge it might face is to infect human beings--profound chromosomal changes occur during the brief period that EHEC passes through the human gastrointestinal tract, leading to gains and losses of virulence determinants. The intensive study of human enteric factors that induce or modulate pathogen chromosome instability could provide important information about host-microbial interactions.

Seasonal variation of Shiga toxin-encoding genes (stx) and detection of E. coli O157 in dairy cattle from Argentina

AIMS

To study the seasonal variation of Shiga toxin-encoding genes (stx) and to investigate the presence of Shiga toxin-producing Escherichia coli (STEC) O157 in cattle belonging to five dairy farms from Argentina.

METHODS AND RESULTS

Rectal swab samples were collected from 360 dairy cows in each season and 115 and 137 calves in autumn and in spring, respectively. The stx were investigated by multiplex PCR and it was used as the indicator for STEC. Samples positives for stx were tested by PCR for eae-gamma1 of E. coli O157 and then subjected to IMS (immunomagnetic separation). In positive animals significant differences in the prevalence of stx between warm and cold seasons were detected. In warm seasons, stx1 + stx2 increased and stx1 decreased, independently of the animal category. The prevalence of STEC O157 in cows and calves were 0.2% and 0.8%, respectively.

CONCLUSIONS

This work provides new data about the occurrence of stx and STEC O157 in dairy herds from Argentina and suggests a relationship between the type of stx and season of year.

SIGNIFICANCE AND IMPACT OF STUDY

The detection of STEC O157 and the seasonality of stx and its types provide an opportunity to improve control strategies designed to prevent contamination of food products and transmission animal-person.

Escherichia coli encoding Shiga toxin 2f as an emerging human pathogen

Escherichia coli harbouring the stx2f gene have been previously reported in pigeons. Here we demonstrate the presence of this allele in human diarrhoeagenic E. coli strains originally classified as atypical enteropathogenic E. coli (aEPEC). Thirty-two stx2f-positive E. coli serotyped as O63:H6, O128:H2, O132:H34, O145:H34, and O178:H7 were found to belong to a large number of clonal groups due to their different MLST-, PFGE- and virulence patterns. The appearance of various stx2f-positive clonal lineages among E. coli reveals emerging clinical significance. Therefore, it seems to be prudent to include stx2f into the diagnostic scope employed for laboratory investigation of enteric infections.

Shiga toxin-producing Escherichia coli serogroups in food and patients, Germany

We compared 61 Shiga toxin–producing Escherichia coli (STEC) serogroups from 448 food isolates with 71 STEC serogroups from 1,447 isolates from patients in Germany. Two thirds (41/61), representing 72% of food isolates, were also found in patients. Serogroups typically isolated from patients with hemolytic uremic syndrome were rarely found in food.

Evaluation of the 'GeneDisc' real-time PCR system for detection of enterohaemorrhagic Escherichia coli (EHEC) O26, O103, O111, O145 and O157 strains according to their virulence markers and their O- and H-antigen-associated genes

AIMS

To evaluate the GeneDisc multiplex real-time PCR assay for detection of enterohaemorrhagic Escherichia coli (EHEC) O26, O103, O111, O145 and O157 strains.

METHODS AND RESULTS

GeneDiscs for detection of genes encoding Shiga toxins (stx), intimins (eae), E. coli O157 (rfbE(O157)) and H7 (fliC(H7)) antigens as well as genes specific for EHEC O26 (wzx(O26)), O103 (wzx(O103)), O111 (wbd1(O111)), O145 (ihp1(O145)) and O157 (ihp1(O157)) were evaluated. The assay was run with native bacteria in 1 h in a GeneDisc Cycler. All genotypes of stx and eae, except stx(2f) and eae-rho, were identified. Escherichia coli strains belonging to O-groups O26, O103, O111, O157 as well as EHEC O145:[H28] strains were specifically detected with this assay. The ihp1(O157) gene was not found specific for EHEC O157. O-rough mutants of EHEC and non-motile EHEC O157 strains were reliably identified with the GeneDisc assay. Two to three colonies of EHEC strains were still detectable in a lawn of 50 000 apathogenic E. coli from agar plates.

CONCLUSIONS

The GeneDisc assay is a specific and reliable assay for detection of major EHEC strains. It is robust enough to detect few EHEC colonies in mixed cultures of bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

The assay is promising for its use in EHEC diagnostics and for EHEC monitoring with different kinds of samples.

Comparing wastewater chemicals, indicator bacteria concentrations, and bacterial pathogen genes as fecal pollution indicators

The objective of this study was to compare fecal indicator bacteria (FIB) (fecal coliforms, Escherichia coli [EC], and enterococci [ENT]) concentrations with a wide array of typical organic wastewater chemicals and selected bacterial genes as indicators of fecal pollution in water samples collected at or near 18 surface water drinking water intakes. Genes tested included esp (indicating human-pathogenic ENT) and nine genes associated with various animal sources of shiga-toxin-producing EC (STEC). Fecal pollution was indicated by genes and/or chemicals for 14 of the 18 tested samples, with little relation to FIB standards. Of 13 samples with <50 EC 100 mL(-1), human pharmaceuticals or chemical indicators of wastewater treatment plant effluent occurred in six, veterinary antibiotics were detected in three, and stx1 or stx2 genes (indicating varying animal sources of STEC) were detected in eight. Only the EC eaeA gene was positively correlated with FIB concentrations. Human-source fecal pollution was indicated by the esp gene and the human pharmaceutical carbamazepine in one of the nine samples that met all FIB recreational water quality standards. Escherichia coli rfbO157 and stx2c genes, which are typically associated with cattle sources and are of potential human health significance, were detected in one sample in the absence of tested chemicals. Chemical and gene-based indicators of fecal contamination may be present even when FIB standards are met, and some may, unlike FIB, indicate potential sources. Application of multiple water quality indicators with variable environmental persistence and fate may yield greater confidence in fecal pollution assessment and may inform remediation decisions.

Production and characterization of rabbit polyclonal sera against Shiga toxins Stx1 and Stx2 for detection of Shiga toxin-producing Escherichia coli

STEC has emerged as an important group of enteric pathogens worldwide. In this study, rabbit polyclonal Stx1 and Stx2 antisera were raised and employed in the standardization of immunoassays for STEC detection. Using their respective antisera, the limit of detection of the toxin was 35.0 pg for Stx1 and 5.4 pg for Stx2. By immunoblotting, these antisera recognized both toxin subunits. Cross-reactivity was observed in the A subunit, but only Stx2 antiserum was able to neutralize the cytotoxicity of both toxins in the Vero cell assay. Six stx-harboring E. coli isolates were analyzed for their virulence traits. They belonged to different serotypes, including the O48:H7, described for the first time in Brazil. Only three strains harbored eae, and the e-hly gene and hemolytic activity was detected in five strains. Three isolates showed new stx2 variants (stx(2v-ha) and stx(2vb-hb)). The ELISA assay detected all six isolates, including one VCA-negative isolate, while the immunodot assay failed to detect one isolate, which was VCA-positive. In contrast, the colony-immunoblot assay detected only one VCA-positive isolate. Our results demonstrate that among the immunoassays developed in this study, the immunodot, and particularly the ELISA, appear as perspective for STEC detection in developing countries.

Cattle density and Shiga toxin-producing Escherichia coli infection in Germany: increased risk for most but not all serogroups

Shiga toxin-producing Escherichia coli (STEC) cause severe gastroenteritis and life-threatening hemolytic-uremic syndrome. For STEC of serogroup O157, association between disease incidence and cattle contact has been established in some countries. For other (non-O157) serogroups, however, accounting for approximately 80% of notified STEC gastroenteritis in Germany, the role of cattle in human infection is less clear. For example, an association of non-O157 STEC infection and cattle density has not been investigated. The aim of this study was thus to investigate a potential association between STEC incidence and cattle density in Germany, with special attention to the non-O157 serogroups. We modeled district-level incidence of notified human STEC cases in relation to cattle density, utilizing German notification data from 2001 through 2003. Cattle numbers came from the national "Proof of Origin and Information Database for Animals." A Bayesian Poisson regression model was used, incorporating independent, as well as spatially correlated, district-level random effects into the analysis. We analyzed 3216 German STEC cases. Cattle density was positively associated with overall STEC incidence. The risk for STEC infection increased by 68% per 100 additional cattle/km(2). The magnitude of the risk estimates differed by serogroup and was greatest for O111. A positive association was found for all major disease-causing serogroups (O26, O103, O111, O128, O145, O157) except O91. The association with serogroup O26 (lowest median age of patients) was only borderline significant. Residual variation indicates that additional factors not under study may also be of importance, and that they may be serogroup- and region-specific, too. In conclusion, this study suggests that living in a cattle-raising region appears to imply risk not only for STEC O157, but also for most non-O157 serogroups. Furthermore, the varying magnitude of this risk and the residual variation found for different serogroups indicate that risk profiles for human STEC infection may be serogroup-specific. This needs to be taken into account in risk factor studies for non-O157 STEC, ideally by reporting risks separately by serogroup.

Sample processing for DNA chip array-based analysis of enterohemorrhagic Escherichia coli (EHEC)

Background

Exploitation of DNA-based analyses of microbial pathogens, and especially simultaneous typing of several virulence-related genes in bacteria is becoming an important objective of public health these days.

Results

A procedure for sample processing for a confirmative analysis of enterohemorrhagic Escherichia coli (EHEC) on a single colony with DNA chip array was developed and is reported here. The protocol includes application of fragmented genomic DNA from ultrasonicated colonies. The sample processing comprises first 2.5 min of ultrasonic treatment, DNA extraction (2×), and afterwards additional 5 min ultrasonication. Thus, the total sample preparation time for a confirmative analysis of EHEC is nearly 10 min. Additionally, bioinformatic revisions were performed in order to design PCR primers and array probes specific to most conservative regions of the EHEC-associated genes. Six strains with distinct pathogenic properties were selected for this study. At last, the EHEC chip array for a parallel and simultaneous detection of genes etpC-stx1-stx2-eae was designed and examined. This should permit to sense all currently accessible variants of the selected sequences in EHEC types and subtypes.

Conclusion

In order to implement the DNA chip array-based analysis for direct EHEC detection the sample processing was established in course of this work. However, this sample preparation mode may also be applied to other types of EHEC DNA-based sensing systems.

Virulence properties and antimicrobial susceptibility of Shiga toxin-producing Escherichia coli strains isolated from healthy cattle from Paraná State, Brazil

The presence of Shiga toxin-producing Escherichia coli (STEC) strains in feces samples of cattle was determined using the cytotoxicity assay on Vero cells and a screening PCR system to detect stx genes. The STEC isolates were serotyped, tested for antimicrobial susceptibility, and analyzed for virulence genes using multiplex PCR. The verocytotoxin-producing E. coli - reverse passive latex agglutination (VTEC-RPLA) assay was also used to detect Shiga toxin production. The frequency of cattle shedding STEC was 36%. The isolates belonged to 33 different serotypes, of which O10:H42, O98:H41, and O159:H21 had not previously been associated with STEC. The most frequent serotypes were ONT:H7 (10%), O22:H8 (7%), O22:H16 (7%), and ONT:H21 (7%). Most of the strains (96%) were susceptible to all antimicrobial agents tested. Shiga toxin was detected by the VTEC-RPLA assay in most (89%) of the STEC strains. The frequency of virulence markers was as follows: stx1, 10%; stx2, 43%; stx1 plus stx2, 47%; ehxA, 44%; eae, 1%; and saa, 38%. Several strains belong to serotypes associated with human disease, and most of them carried a stx2-type gene, suggesting that they represent a risk to human health. The screening PCR assay showed fewer false-negative results for STEC than the Vero-cell assay and is suitable for laboratory routine.

Characterization of attaching and effacing Escherichia coli (AEEC) isolated from pigs and sheep

Background

Attaching and effacing Escherichia coli (AEEC) are characterized by their ability to cause attaching-and-effacing (A/E) lesions in the gut mucosa of human and animal hosts leading to diarrhoea. The genetic determinants for the production of A/E lesions are located on the locus of enterocyte effacement (LEE), a pathogenicity island that also contains the genes encoding intimin (eae). This study reports data on the occurrence of eae positive E. coli carried by healthy pigs and sheep at the point of slaughter, and on serotypes, intimin variants, and further virulence factors of isolated AEEC strains.

Results

Faecal samples from 198 finished pigs and 279 sheep were examined at slaughter. The proportion of eae positive samples was 89% for pigs and 55% for sheep. By colony dot-blot hybridization, AEEC were isolated from 50 and 53 randomly selected porcine and ovine samples and further characterized. Strains of the serotypes O2:H40, O3:H8 and O26:H11 were found in both pigs and sheep. In pigs O2:H40, O2:H49, O108:H9, O145:H28 and in sheep O2:H40, O26:H11, O70:H40, O146:H21 were the most prevalent serotypes among typable strains. Eleven different intimin types were detected, whereas γ2/θ was the most frequent, followed by β1, ε and γ1. All but two ovine strains tested negative for the genes encoding Shiga toxins. All strains tested negative for the bfpA gene and the EAF plasmid. EAST1 (astA) was present in 18 of the isolated strains.

Conclusion

Our data show that pigs and sheep are a source of serologically and genetically diverse intimin-harbouring E. coli strains. Most of the strains show characteristics of atypical enteropathogenic E. coli. Nevertheless, there are stx-negative AEEC strains belonging to serotypes and intimin types that are associated with classical enterohaemorrhagic E. coli strains (O26:H11, β1; O145:H28, γ1).

Phenotypic and genotypic characterization of verotoxin-producing Escherichia coli O103:H2 isolates from cattle and humans

Characterization of important non-O157 verotoxin-producing Escherichia coli (VTEC) has lagged considerably behind that of O157:H7 strains. This study characterized 91 VTEC O103:H2 strains from bovine and human sources and of North American and European origins by virulence or putative virulence genes, pulsed-field gel electrophoresis (PFGE) patterns, plasmid profiles, antimicrobial resistance, and colicin production. All strains were positive for vt1 and eae-epsilon; 97% were positive for ehxA; and all were negative for hlyA. Two strains carried vt2. There were 66 PFGE patterns grouped in six clusters, and there were 25 different plasmid profiles. Plasmid-encoded katP and etp genes were significantly more frequent in European than in North American human strains. The distribution of selected phenotypes was as follows: enterohemorrhagic E. coli (EHEC) hemolysin, 95%; colicin production, 38%; antimicrobial resistance, 58%. All the strains were negative for the alpha-hemolytic phenotype. In conclusion, the VTEC O103:H2 strains were diverse, as shown by PFGE, plasmid profiles, virulence markers, and antimicrobial resistance patterns, and all strains showed an EHEC hemolytic phenotype instead of the alpha-hemolytic phenotype that has been shown previously.

Prevalence and characteristics of Shiga toxin-producing Escherichia coli in Swiss raw milk cheeses collected at producer level

The aim of this study was to describe the prevalence, serotypes, and virulence genes of Shiga toxin-producing Escherichia coli (STEC) isolated from raw milk cheese samples collected at the producer level with the purpose of determining whether raw milk cheeses in Switzerland represent a potential source of STEC pathogenic for humans. Raw milk cheese samples (soft cheese, n = 52; semihard and hard cheese, n = 744; all produced from Swiss cows', goats', and sheep's milk) collected at the producer level throughout Switzerland within the national sampling plan during the period of March 2006 to December 2007 were analyzed. Of the 432 cheese samples obtained in the year 2006 and the 364 samples obtained in the year 2007, 16 (3.7%) and 23 (6.3%), respectively, were found to be stx positive. By colony dot-blot hybridization, non-O157 STEC strains were isolated from 16 samples. Of the 16 strains, 11 were typed into 7 E. coli O groups (O2, O15, O22, O91, O109, O113, O174), whereas 5 strains were nontypeable (ONT). Among the 16 STEC strains analyzed, stx(1) and stx(2) variants were detected in 1 and 15 strains, respectively. Out of the 15 strains with genes encoding for the Stx2 group, 4 strains were positive for stx(2), 6 strains for stx(2d2), 2 strains for stx(2-O118), 1 strain for stx(2-06), 1 strain for stx(2g), 1 strain for stx(2) and stx(2d2), and 1 strain for stx(2) and stx(2g). Furthermore, 3 STEC strains harbored E-hlyA as a further putative virulence factor. None of the strains tested positive for eae (intimin). Results obtained in this work reinforce the suggestion that semihard raw milk cheese may be a potential vehicle for transmission of pathogenic STEC to humans.

Characterisation of Escherichia coli O157 strains from humans, cattle and pigs in the North-West Province, South Africa

Escherichia coli O157 strains cause diseases in humans that result from the consumption of food and water contaminated with faeces of infected animals and/or individuals. The objectives of this study were to isolate and characterise E. coli O157 strains from humans, cattle and pigs and to determine their antibiotic resistant profiles as well as detection of virulence genes by PCR. Eight hundred faecal samples were analysed for typical E. coli O157 and 76 isolates were positively identified as E. coli O157 strains. 16S rRNA sequence data were used to confirm the identity of the isolates. Susceptibility profiles to 9 antibiotics were determined and the multiple antibiotic resistant (MAR) patterns were compiled. A large proportion (52.6%-92.1%) of the isolates from pigs, cattle and humans were resistant to tetracycline, sulphamethoxazole and erythromycin. Thus the phenotype Smx-T-E (sulphamethozaxole-tetracycline-erythromycin) was present in most of the predominant MAR phenotypes obtained. Cluster analysis of antibiotic resistances revealed a closer relationship between isolates from pig and human faeces than cattle and humans. PCR were performed to amplify STEC virulence and tetracycline resistance gene fragments. A tetB gene fragment was amplified among the isolates. Eighteen (60%) of the isolates possessed the hlyA gene and 7(23.3%) the eae gene while only 5(16.7%) possessed both genes. Although shiga toxin genes were detected in the E. coli O157:H7 positive control strain none of the isolates that were screened possessed these genes. In a related study we reported that the prevalence of E. coli O157 was higher in pigs than cattle and humans. A high market demand for pork and beef in South Africa amplifies the risk that diseased animals pose to human health. This highlighted the need for proper hygiene management to reduce the prevalence of E. coli O157 in farm animals and prevent the spread from animals to humans.

Prevalence and genetic characterization of shiga toxin-producing Escherichia coli isolates from slaughtered animals in Bangladesh

To determine the prevalence of Shiga toxin (Stx)-producing Escherichia coli (STEC) in slaughter animals in Dhaka, Bangladesh, we collected rectal contents immediately after animals were slaughtered. Of the samples collected from buffalo (n = 174), cows (n = 139), and goats (n = 110), 82.2%, 72.7%, and 11.8% tested positive for stx(1) and/or stx(2), respectively. STEC could be isolated from 37.9%, 20.1%, and 10.0% of the buffalo, cows, and goats, respectively. STEC O157 samples were isolated from 14.4% of the buffalo, 7.2% of the cows, and 9.1% of the goats. More than 93% (n = 42) of the STEC O157 isolates were positive for the stx(2), eae, katP, etpD, and enterohemorrhagic E. coli hly (hly(EHEC)) virulence genes. STEC O157 isolates were characterized by seven recognized phage types, of which types 14 (24.4%) and 31 (24.4%) were predominant. Subtyping of the 45 STEC O157 isolates by pulsed-field gel electrophoresis showed 37 distinct restriction patterns, suggesting a heterogeneous clonal diversity. In addition to STEC O157, 71 STEC non-O157 strains were isolated from 60 stx-positive samples from 23.6% of the buffalo, 12.9% of the cows, and 0.9% of the goats. The STEC non-O157 isolates belonged to 36 different O groups and 52 O:H serotypes. Unlike STEC O157, most of the STEC non-O157 isolates (78.9%) were positive for stx(1). Only 7.0% (n = 5) of the isolates were positive for hly(EHEC), and none was positive for eae, katP, and etpD. None of the isolates was positive for the iha, toxB, and efa1 putative adhesion genes. However, 35.2% (n = 25), 11.3% (n = 8), 12.7% (n = 9), and 12.7% (n = 9) of the isolates were positive for the lpf(O113), saa, lpfA(O157/01-141), and lpfA(O157/OI-154) genes, respectively. The results of this study provide the first evidence that slaughtered animals like buffalo, cows, and goats in Bangladesh are reservoirs for STEC, including the potentially virulent STEC strain O157.

Evaluation of major types of Shiga toxin 2E-producing Escherichia coli bacteria present in food, pigs, and the environment as potential pathogens for humans

Shiga toxin 2e (Stx2e)-producing strains from food (n = 36), slaughtered pigs (n = 25), the environment (n = 21), diseased pigs (n = 19), and humans (n = 9) were investigated for production of Stx2e by enzyme-linked immunosorbent assay, for virulence markers by PCR, and for their serotypes to evaluate their role as potential human pathogens. Stx2e production was low in 64% of all 110 strains. Stx2e production was inducible by mitomycin C but differed considerably between strains. Analysis by nucleotide sequencing and transcription of stx(2e) genes in high- and low-Stx2e-producing strains showed that toxin production correlated with transcription rates of stx(2e) genes. DNA sequences specific for the int, Q, dam, and S genes of the stx(2e) bacteriophage P27 were found in 109 strains, indicating cryptic P27-like prophages, although 102 of these were not complete for all genes tested. Genes encoding intimin (eae), enterohemorrhagic Escherichia coli hemolysin (ehx), or other stx(1) or stx(2) variants were not found, whereas genes for heat-stable enterotoxins STI, STII, or EAST1 were present in 54.5% of the strains. Seven major serotypes that were associated with diseased pigs (O138:H14, O139:H1, and O141:H4) or with slaughter pigs, food, and the environment (O8:H4, O8:H9, O100:H30, and O101:H9) accounted for 60% of all Stx2e strains. The human Stx2e isolates did not belong to these major serotypes of Stx2e strains, and high production of Stx2e in human strains was not related to diarrheal disease. The results from this study and other studies do not point to Stx2e as a pathogenicity factor for diarrhea and hemolytic uremic syndrome in humans.

Serogroups, atypical biochemical characters, colicinogeny and antibiotic resistance pattern of Shiga toxin-producing Escherichia coli isolated from diarrhoeic calves in Gujarat, India

This study was designed to investigate the antibiotic resistance, colicinogeny, serotyping and atypical biochemical characteristics of 41 Shiga toxin-producing Escherichia coli (STEC) strains detected using polymerase chain reaction from 90 E. coli strains isolated from 46 diarrhoeic calves. The STEC strains belonged to 14 different serogroups. Seventeen per cent of the STEC strains carried the eaeA gene while 14.28% of the 49 non-STEC strains were eaeA positive. Twenty eight (68.29%) of the 41 STEC strains were rhamnose non-fermentors. All the STEC strains revealed resistance to at least three of the antibiotics tested. 100% resistance was found against kanamycin and cephalexin followed by cephaloridine, enrofloxacin, amikacin, ampicillin, tetracycline, ceftiofur, ciprofloxacin, colistin and co-trimoxazole. Eighteen (44%) of the STEC strains produced colicin and all these colicinogenic strains were resistant to three or more antibiotics. Eleven STEC strains (26.82%) showed urease activity. The results of this study suggest that diarrhoeic calves are an important reservoir of STEC strains that are potentially pathogenic for farm animals and humans. Moreover, rhamnose fermentation, colicinogeny and atypical biochemical behaviour, such as urease activity, may serve as important markers or diagnostic tools for epidemiological surveys to trace the source of infection in disease outbreaks.

Shedding of food-borne pathogens and microbiological carcass contamination in rabbits at slaughter

To obtain microbiological data from rabbits at slaughter, 500 fecal samples and 500 carcasses samples were examined. All samples tested negative for Listeria and Salmonella. Campylobacter were detected in two fecal samples. Of the 500 fecal samples, 45.8% tested positive for eae (intimin), 1.2% for stx (Shiga toxin), and 1.8% for both eae and stx. By colony hybridization, 56 eae positive Escherichia coli strains were isolated. Among them, 27 strains (48.2%) were of the serotypes O178:H7 and O153:H7, whereas 15 strains (26.8%) belonged to a serogroup that has not yet been described (O(CB10681):H7). All strains possessed intimin beta1 and the translocated intimin receptor (tir) capable of being tyrosine phosphorylated. None of the strains harbored the genes for Shiga toxins, EAST1 (astA), bundlin (bfpA), or the EAF plasmid. Slaughter rabbits therefore constitute a reservoir for certain atypical enteropathogenic Escherichia coli. On rabbit carcasses, average total bacterial counts accounted for 3.3 log CFU cm(-2). Enterobacteriaceae and coagulase positive staphylococci (CPS) were detected on 118 (23.6%) and 153 (30.6%) carcasses, respectively. Enterobacteriaceae and CPS counts of positive samples were mainly <1.5 log CFU cm(-2). Among 153 selected CPS isolates, 98.7% were identified as Staphylococcus aureus. None of the 151 isolated strains harbored the gene for methicillin resistance (mecA). Genes for staphylococcal enterotoxins (SE) were detected in 102 strains. The combinations of seg and sei (53 strains) and sed, seg, sei, and sej (27 strains) dominated.

Characterisation of Shiga toxin-producing Escherichia coli O157 strains isolated from humans in Argentina, Australia and New Zealand

Background

Shiga toxin-producing Escherichia coli (STEC) is an important cause of bloody diarrhoea (BD), non-bloody diarrhoea (NBD) and the haemolytic uraemic syndrome (HUS). In Argentina and New Zealand, the most prevalent STEC serotype is O157:H7, which is responsible for the majority of HUS cases. In Australia, on the other hand, STEC O157:H7 is associated with a minority of HUS cases. The main aims of this study were to compare the phenotypic and genotypic characteristics of STEC O157 strains isolated between 1993 and 1996 from humans in Argentina, Australia and New Zealand, and to establish their clonal relatedness.

Results

Seventy-three O157 STEC strains, isolated from HUS (n = 36), BD (n = 20), NBD (n = 10), or unspecified conditions (n = 7) in Argentina, Australia and New Zealand, were analysed. The strains were confirmed to be E. coli O157 by biochemical tests and serotyping. A multiplex polymerase chain reaction (PCR) was used to amplify the stx₁, stx₂ and rfb_O157 genes and a genotyping method based on PCR-RFLP was used to determine stx₁ and stx₂ variants. This analysis revealed that the most frequent stx genotypes were stx₂/stx_{2c (vh-a)} (91%) in Argentina, stx₂ (89%) in New Zealand, and stx₁/stx₂ (30%) in Australia. No stx₁-postive strains were identified in Argentina or New Zealand. All strains harboured the eae gene and 72 strains produced enterohaemolysin (EHEC-Hly). The clonal relatedness of strains was investigated by phage typing and pulsed-field gel electrophoresis (PFGE). The most frequent phage types (PT) identified in Argentinian, Australian, and New Zealand strains were PT49 (n = 12), PT14 (n = 9), and PT2 (n = 15), respectively. Forty-six different patterns were obtained by XbaI-PFGE; 37 strains were grouped in 10 clusters and 36 strains showed unique patterns. Most clusters could be further subdivided by BlnI-PFGE.

Conclusion

STEC O157 strains isolated in Argentina, Australia, and New Zealand differed from each other in terms of stx-genotype and phage type. Additionally, no common PFGE patterns were found in strains isolated in the three countries. International collaborative studies of the type reported here are needed to detect and monitor potentially hypervirulent STEC clones.

Prevalence, characterisation and clinical profiles of Shiga toxin-producing Escherichia coli in The Netherlands

Detection of Shiga toxin-producing Escherichia coli (STEC) in The Netherlands is traditionally limited to serogroup O157. To assess the relative importance of STEC, including non-O157 serogroups, stool samples submitted nationwide for investigation of enteric pathogens or diarrhoea were screened with real-time PCR for the presence of the Shiga toxin genes. Patients were selected if their stool contained blood upon macroscopic examination, if they had a history of bloody diarrhoea, were diagnosed with haemolytic uraemic syndrome, or were aged <6 years (irrespective of the bloody aspect of the stool). PCR-positive stools were forwarded to a central laboratory for STEC isolation and typing. In total, 4069 stools were examined, with 68 (1.7%) positive PCR results. The highest prevalence was for stools containing macroscopic blood (3.5%), followed by stools from patients with a history of bloody diarrhoea (2.4%). Among young children, the prevalence (1.0%) was not significantly higher than among random, non-bloody, stool samples from diarrhoeal patients (1.4%). STEC strains were isolated from 25 (38%) PCR-positive stools. Eleven O-serogroups were detected, including five STEC O157 strains. As serogroup O157 represented only 20% of the STEC isolates, laboratories should be encouraged to use techniques enabling them to detect non-O157 serogroups, in parallel with culture, for isolation and subsequent characterisation of STEC strains for public health surveillance and detection of outbreaks.

Characterization of Shiga toxin-producing Escherichia coli isolates associated with two multistate food-borne outbreaks that occurred in 2006

Shiga toxin-producing Escherichia coli isolates from two 2006 outbreaks were compared to other O157:H7 isolates for virulence genotype, biofilm formation, and stress responses. Spinach- and lettuce-related-outbreak strains had similar pulsed-field gel electrophoresis patterns, and all carried both stx2 and stx2c variant genes. Cooperative biofilm formation involving an E. coli O157:H7 strain and a non-O157:H7 strain was also demonstrated.

Differential binding of Shiga toxin 2 to human and murine neutrophils

Shiga toxins (Stx1 and Stx2) are responsible for initiating haemolytic uraemic syndrome, a serious extraintestinal complication caused by enterohaemorrhagic Escherichia coli O157 : H7 infection in humans. Shiga toxins are classical AB(5)-type exotoxins, consisting of a globotriaosylceramide (Gb(3))-binding B subunit pentamer and an enzymic A subunit. It is demonstrated in this study that Stx2 binds to human neutrophils by a non-classical mechanism that is independent of Gb(3). In contrast, the investigation revealed that Stx2 binds to murine neutrophils by the classical Gb(3)-dependent mechanism. Moreover, whereas the human serum amyloid P (HuSAP) component inhibited Stx2 binding to murine neutrophils, HuSAP increased Stx2 binding to human neutrophils by 84.2 % (P< or =0.002, Student's t-test). These observations may explain why HuSAP protects mice from the lethal effects of Stx2, whereas there is no indication that HuSAP plays a similar protective role in humans infected by E. coli O157 : H7.

lfnA from Pseudomonas aeruginosa O12 and wbuX from Escherichia coli O145 encode membrane-associated proteins and are required for expression of 2,6-dideoxy-2-acetamidino-L-galactose in lipopolysaccharide O antigen

The rare sugar 2,6-dideoxy-2-acetamidino-L-galactose (L-FucNAm) is found only in bacteria and is a component of cell surface glycans in a number of pathogenic species, including the O antigens of Pseudomonas aeruginosa serotype O12 and Escherichia coli O145. P. aeruginosa is an important opportunistic pathogen, and the O12 serotype is associated with multidrug-resistant epidemic outbreaks. O145 is one of the classic non-O157 serotypes associated with Shiga toxin-producing, enterohemorrhagic E. coli. The acetamidino (NAm) moiety of L-FucNAm is of interest, because at neutral pH it contributes a positive charge to the cell surface, and we aimed to characterize the biosynthesis of this functional group. The pathway is not known, but expression of NAm-modified sugars coincides with the presence of a pseA homologue in the relevant biosynthetic locus. PseA is a putative amidotransferase required for synthesis of a NAm-modified sugar in Campylobacter jejuni. In P. aeruginosa O12 and E. coli O145, the pseA homologues are lfnA and wbuX, respectively, and we hypothesized that these genes function in L-FucNAm biosynthesis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and nuclear magnetic resonance analysis of the lfnA mutant O-antigen structure indicated that the mutant expresses 2,6-dideoxy-2-acetamido-L-galactose (L-FucNAc) in place of L-FucNAm. The mutation could be complemented by expression of either His(6)-tagged lfnA or wbuX in trans, confirming that these genes are functional homologues and that they are required for NAm moiety synthesis. Both proteins retained their activity when fused to a His(6) tag and localized to the membrane fraction. These data will assist future biochemical investigation of this pathway.

Molecular characterization reveals similar virulence gene content in unrelated clonal groups of Escherichia coli of serogroup O174 (OX3)

Most severe illnesses that are attributed to Shiga toxin-producing Escherichia coli are caused by isolates that also carry a pathogenicity island called the locus of enterocyte effacement (LEE). However, many cases of severe disease are associated with LEE-negative strains. We characterized the virulence gene content and the evolutionary relationships of Escherichia coli isolates of serogroup O174 (formerly OX3), strains of which have been implicated in cases of hemorrhagic colitis and hemolytic uremic syndrome. A total of 56 isolates from humans, farm animals, and food were subjected to multilocus virulence gene profiling (MVGP), and a subset of 16 isolates was subjected to multilocus sequence analysis (MLSA). The MLSA revealed that the O174 isolates fall into four separate evolutionary clusters within the E. coli phylogeny and are related to a diverse array of clonal groups, including enteropathogenic E. coli 2 (EPEC 2), enterohemorrhagic E. coli 2 (EHEC 2), and EHEC-O121. Of the 15 genes that we surveyed with MVGP, only 6 are common in the O174 strains. The different clonal groups within the O174 serogroup appear to have independently acquired and maintained similar sets of genes that include the Shiga toxins (stx1 and stx2) and two adhesins (saa and iha). The absence of certain O island (OI) genes, such as those found on OI-122, is consistent with the notion that certain pathogenicity islands act cooperatively with the LEE island.

Phenotypical characteristics of Shiga-like toxin Escherichia coli isolated from sheep dairy products

AIMS

To analyse phenotypical characteristics of Shiga toxin-producing Escherichia coli (STEC) strains from ovine origin.

METHODS AND RESULTS

A total of 13 STEC strains (eight O157 and five non-O157) isolated from sheep dairy products were used in this study. Biochemical traits, motility, haemolytic activity, resistance to tellurite-cefixime, maximum growth temperature and antibiotic resistance were determined. The STEC strains were grouped into nine biochemical and physiological biotypes (five for the O157 and four for the non-O157 strains). All STEC strains showed resistance to bacitracin, cloxacilin, penicillin and tylosin.

CONCLUSIONS

Different biotypes and antibiotic resistance patterns of STEC isolated from sheep dairy products were observed.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work will be a contribution to the better characterization of STEC isolated from sheep dairy products, which have, to date, been scarcely studied, and to the better understanding of the risks associated with its consumption.

Explaining unexplained diarrhea and associating risks and infections

Gastrointestinal illnesses are common afflictions. However, knowledge of their etiology is often lacking. Moreover, most cases of infections with reportable enteric pathogens (Campylobacter jejuni, Escherichia coli O157:H7, Salmonella, Shigella, Yersinia, Cryptosporidia and Giardia) have sporadic modes of acquisition, yet control measures are often biased towards mitigation of risks discerned by outbreak analysis. To determine the etiology of unexplained diarrhea it is important to study populations that can be matched to appropriate controls and to couple thorough classic microbiologic evaluation on receipt of specimens with archiving and outgrowth capabilities. Research evaluations should address the potential roles of a broad panel of candidate bacterial pathogens including diarrheagenic E. coli, Listeria monocytogenes, Helicobacters and jejuni Campylobacters, and also apply novel massively parallel sequencing and nucleic acid detection technologies that allow the detection of viral pathogens. To fill voids in our knowledge regarding sources of known enteric pathogens it will be critical to extend case-control studies to assess risk factors and exposures to patients with non-epidemic illnesses and to appropriate controls. By filling these gaps in our knowledge it should be possible to formulate rational prevention mechanisms for human gastrointestinal illnesses.

Serotypes and virutypes of enteropathogenic and enterohaemorrhagic Escherichia coli strains from stool samples of children with diarrhoea in Germany

AIMS

To investigate the prevalence of traditional and emerging types of enteropathogenic (EPEC) and enterohaemorrhagic Escherichia coli (EHEC) strains in stool samples from children with diarrhoea and to characterize their virulence genes involved in the attaching and effacing (A/E) phenotype.

METHODS AND RESULTS

Serological and PCR-based methods were used for detection and isolation of EPEC and EHEC strains from 861 stool samples from diarrhoeic children. Agglutination with traditional EPEC and EHEC O-group-specific antisera resulted in detection of 38 strains; 26 of these carried virulence factors of EPEC or EHEC. PCR screening for the eae gene resulted in isolation of 97 strains, five carried genes encoding Shiga toxins (stx), one carried the bfpA gene and 91 were atypical EPEC. The 97 EPEC and EHEC strains were divided into 36 O-serogroups and 21 H-types, only nine strains belonged to the traditional EPEC O-groups O26, O55, O86 and O128. In contrast, EPEC serotypes O28:H28, O51:H49, O115:H38 and O127:H40 were found in multiple cases. Subtyping the virulence factors intimin, Tir and Tir-cytoskeleton coupling effector protein (TccP)/TccP2 resulted in further classification of 93.8% of the 97 strains.

CONCLUSIONS

Our findings show a clear advantage of the eae-PCR over the serological detection method for identification of EPEC and EHEC strains from human patients.

SIGNIFICANCE AND IMPACT OF THE STUDY

Molecular detection by the eae-PCR followed by serotyping and virutyping is useful for monitoring trends in EPEC and EHEC infections and to discover their possible reservoirs.