Studies on the enterotoxigenicity of environmental Escherichia coli, belonging to serotypes normally considered enterotoxigenic.

Fifteen strains of Escherichia coli which had been collected in previous studies from animals and meat were studied. They belonged to serotypes considered enterotoxigenic and were examined for the production of the heat-labile and heat-stable enterotoxins. Only one of these strains (O8.Hnt) isolated from a cowpat in Cheshire produced heat-labile enterotoxin. Another strain (O8.H9) isolated from a cowpat in another part of Cheshire gave results suggesting production of small amounts of the heat-stable enterotoxin. The ecological aspects of these results are discussed.     

Studies on the enterotoxigenicity of environmental Escherichia coli, belonging to serotypes normally considered enterotoxigenic

Fifteen strains of Escherichia coli which had been collected in previous studies from animals and meat were studied. They belonged to serotypes considered enterotoxigenic and were examined for the production of the heat-labile and heat-stable enterotoxins. Only one of these strains (O8.Hnt) isolated from a cowpat in Cheshire produced heat-labile enterotoxin. Another strain (O8.H9) isolated from a cowpat in another part of Cheshire gave results suggesting production of small amounts of the heat-stable enterotoxin. The ecological aspects of these results are discussed.     

Virulence genotypes and serotypes of verotoxigenic Escherichia coli isolated from cattle and foods in Argentina

Virulence factors of Verotoxin-producing Escherichia coli(VTEC) strains isolated from hamburgers and ground beef were studied in Argentina by PCR. Their virulence profiles were correlated with those corresponding to strains isolated from calves and adult cattle. Most virulent profiles (VTs⁺ eae ⁺Mp⁺) were present in E. colifrom healthy and diarrheic calves corresponding to O5:H-, O5:H27, O20:H?, O26:H11, O38:H?, O103:H-, O103:H2, O111:H-, O118:H16, O165:H-serotypes. The presence of the eaegene was significantly more frequent among VTEC strains isolated from calves (20/26; 76%) than from adult cattle (1/39; 2.5%) (p< 0.005). VT2⁺ eae ^? E. coliwas prevalent in foods and adult cattle at slaughterhouse. The prevalence of the eaegene was similar between VTEC strains isolated from meat (0/21) and adult cattle (1/39; 2.5%) which constitutes the main population processed at slaughterhouses in Argentina. Serotyping showed that VTEC strains were distributed among 31 serotypes, some of which (O20:H19, O91:H21, O113:H21, O116:H21, O117:H7, O171:H2, OX3:H21) were shared between bovine and food strains. These O serogroups have been isolated from cases of haemorrhagic colitis (HC) and haemolytic-uraemic syndrome (HUS) in humans in several continental European countries. This study confirms the role of cattle as a reservoir of many VTEC serotypes other than O157:H7 and represents a base for future diagnostic, prevention and control strategies of EHEC in this country. In addition, this study affirms the advantages of PCR-based screening of E. coliisolates given the finding of so many verotoxin-producing strains.     

Sequence heterogeneity of the eae gene and detection of verotoxin-producing Escherichia coli using serotype-specific primers.

The distribution of the Escherichia coli attaching and effacing (eae) gene in strains of verotoxin-producing E. coli (VTEC) isolated from cattle and humans was studied. The majority of strains isolated from humans with bloody diarrhoea or HUS and cattle with severe diarrhoea were eae positive (82 and 83% respectively). In contrast, 59% of VTEC isolated from asymptomatic cattle were eae negative and of the remaining 41% that were eae positive, the majority were serotype O157. H7. The nucleotide sequence of the 3'' end of the eae gene of enteropathogenic E. coli (EPEC) of serotype O55. H7 was found to be almost identical to that of serotype O157. H7. Specific primers are described which detect the eae sequences of VTEC serotypes O157. H7, O157. H-, and EPEC serotypes O55. H7 and O55. H-. The nucleotide sequence of the 3'' end of the eae gene of serotype O111. H8 differed significantly from that of O157. H7. Primers were developed to specifically identify the eae sequences of VTEC serotypes O111. H- and O111. H8. We conclude that whereas the majority of VTEC associated with disease in cattle and humans possess the eae gene, the gene itself may not be necessary to produce haemorrhagic colitis and HUS. Sequence heterogeneity in the 3'' end of eae alleles of VTEC permits specific identification of subsets of these organisms.     

Isolation of verocytotoxin-producing Escherichia coli from milk filters in south-western Ontario

A total of 1012 milk filters collected from 498 dairy farms in south-western Ontario during three study periods (December 1985-March 1986) were tested for the presence of verocytotoxin-producing Escherichia coli (VTEC). VTEC were detected and isolated using a Vero cell assay. Supernatants from 20 of the milk filter cultures had verocytotoxic activity and 7 VTEC strains were isolated from these positive samples. The prevalence of VTEC in the samples in each of the three study periods were 0.44, 0.65 and 0.99% respectively. All seven VTEC strains isolated were sensitive to commonly used antimicrobial agents. The serotypes of these strains were O 26.H11, O43.H2, O 153.H25, O ?. H8, O? .H19, O ?. non-motile, and Orough.H19. Two of these serotypes (O 153.H25 and O 26.H11) have previously been associated with disease in humans.     

Prevalence and characteristics of Escherichia coli serotype O157:H7 and other verotoxin-producing E. coli in healthy cattle.

From February to July of 1994, 328 faecal samples from 32 herds were collected and verotoxin-producing Escherichia coli (VTEC) found on 84% of the farms. The proportion of animals infected varied from 0-63%. VTEC were recovered from 52 (20%) of 257 cows and from 16 (23%) of 71 calves. Although the VTEC belonged to 25 different serogroups, 7 (O8, O20, O22, O77, O113, O126 and O162) accounted for 46% of strains. Nearly 45% of the strains. Nearly 45% of the 83 bovine VTEC strains belonged to serogroups associated with haemorrhagic colitis and haemolytic uraemic syndrome in humans. However, only 2 (2%) of 83 VTEC strains isolated from cattle belonged to enterohaemorrhagic E. coli (EHEC) serotypes (O26:H11 and O157:H7), and only 8 (10%) were positive for the attaching and effacing E. coli (eae) gene sequence. Polymerase chain reaction (PCR) showed that 17 (20%) of VTEC strains carried VT1 genes, 43 (52%) possessed VT2 genes, and 23 (28%) carried both VT1 and VT2 genes. Characterization of VTEC isolates revelated a heterogeneous population in terms of serogroup and toxin type in the positive herds. This study confirms that healthy cattle are a reservoir of VTEC, but, the absence of eae genes in most bovine VTEC strains suggests that they may be less virulent for humans than eae-positive EHEC.     

Prevalence, structure and expression of urease genes in Shiga toxin-producing Escherichia coli from humans and the environment

A component of the ure gene cluster in E. coli, ureC, encodes a subunit of urease. We have investigated the distribution of ureC in 202 Shiga toxin-producing E. coli (STEC) strains from Austria belonging to 61 different serotypes. These strains were of human (n=150), animal (n=38), and food (n=14) origin. ureC was present in all 72 E. coli O157:H7 and O157:NM (non-motile) strains, as well as in all 29 strains of serotypes O26:H11/NM, O111:H8/NM and O145:NM. In contrast, none of eight sorbitol-fermenting E. coli O157:NM were ureC-positive. ureC occurred significantly more frequently among STEC that carry eae (113 of 132; 85.6%) than among eae-negative STEC strains (four of 70; 5.7%; p<0.0001). However, only 4 (2%) of the 202 strains (3.4% of ureC positive strains) expressed urease activity. There was no significant association (p=0.56) between urease expression and the source of the isolates (humans vs. animals). Nucleotide sequence analysis of PCR amplicons derived from all seven genes of the ure cluster in STEC of 10 different serotypes demonstrated a high degree of homology (>or=99%), indicating a recent acquisition of not necessarily expressed ure genes.     

Investigation of human infections with verocytotoxin-producing strains of Escherichia coli (VTEC) belonging to serogroup O118 with evidence for zoonotic transmission

Twenty verocytotoxigenic Escherichia coli (VTEC) O118 strains isolated between 1996 and 1998 from human patients in Germany were analysed for their serotypes, their virulence markers and their epidemiological relatedness. Three strains were typed as O118:H12, these carried only the VT2d-Ount variant gene and were not associated with diarrhoea or haemolytic uraemic syndrome (HUS). Seventeen strains were serotyped as O118:H16 or O118:non-motile (NM). These carried all the genes for VTI, eae and EHEC-haemolysin. The O118:H16/NM strains were from diarrhoea (13 cases) and HUS (2 cases). Sixteen of the patients were young infants and most infections were associated with a rural environment. Evidence for zoonotic transmission from cattle to humans was found in two cases. The epidemiological relationship between the human and bovine O118:H16/NM isolates was indicated by homogeneous plasmid patterns and by very similar XbaI restriction patterns obtained by pulsed-field gel electrophoresis. VTEC O118:H16/NM are emerging pathogens in Germany and should be classified as new enterohaemorrhagic E. coli (EHEC) types.     

Antibiotic resistance in Salmonella enterica serotypes Typhimurium, Enteritidis and Infantis from human infections, foodstuffs and farm animals in Italy

The antimicrobial susceptibility of isolates of Salmonella enterica serotypes Typhimurium, Enteritidis, and Infantis isolated from humans, foodstuffs and farm animals in Italy between 1999 and 2001 was examined. All the isolates were susceptible to cefotaxime and ciprofloxacin, but high rates of resistance were observed for several other drugs, especially for S. Typhimurium. The rates of resistance and multiresistance were generally higher among animal and food isolates than in human strains; conversely, no significant difference was observed between animal and food isolates. Among S. Typhimurium, multiresistance was more common in bovine, poultry and rabbit strains than in swine isolates, and was rare in strains from pigeon. Resistance to trimethoprim sulphamethoxazole was mainly found in isolates of swine and human origin. This study confirms the role of livestock as a reservoir of drug-resistant Salmonella spp. and underlines the need for integrated surveillance systems of antibiotic resistance that consider isolates not only from human disease but also from the animal reservoirs and the food vehicles.     

Escherichia coli: on-farm contamination of animals

Escherichia coli is one of the main inhabitants of the intestinal tract of most mammalian species, including humans, and birds. Shiga toxin-producing E. coli (STEC), also called verotoxinogenic E. coli, usually do not cause disease in animals but may cause watery diarrhoea, haemorrhagic colitis, and/or haemolytic uraemic syndrome in humans. Zoonotic STEC include the O157:H7 strains and, with increasing frequency, certain non-O157 strains. The importance of non-O157 zoonotic strains is probably underestimated as they have been less well characterised and are more difficult to detect in samples than O157:H7. Another large subset of STEC strains has been isolated from animals but has not, at the present time, been associated with disease in animals or humans. Cattle and other ruminants are the most important reservoir of zoonotic STEC, which are transmitted to humans through the ingestion of foods or water contaminated with animal faeces, or through direct contact with the infected animals or their environment. The main sources of STEC infection of cattle on-farm are the drinking water, the feed, and the immediate environment of the animal. Risk factors that have been identified for infection of animals with O157 STEC include age, weaning, movement of the animals, season, feed composition, and the ability of the bacteria to persist in the environment. On-farm control of the zoonotic risk of human infection with STEC should primarily target the main source of contamination: the animal reservoir. Various strategies to reduce intestinal colonisation of cattle by zoonotic STEC have been tried with varying results, including vaccination, treatment with probiotics, such as direct-fed microbials or competitive exclusion, administration of bacteriophages, and modification of the diet.     

Cross reactivity of enterohemorrhagic Escherichia coli O157:H7-specific sera with non-O157 serotypes

Escherichia coli O157:H7 is an important food- and water-borne pathogen of humans, causing Hemorrhagic Colitis and Haemolytic Uremic Syndrome. Colonization of both cattle and human hosts is mediated through the action of effector molecules secreted via a Type III secretion system, a mechanism shared by other enterohemorrhagic E. coli (EHEC). We recently reported that vaccination of cattle with Type III-secreted proteins (TTSPs) resulted in decreased shedding of the organism following both experimental infection as well as under conditions of natural exposure. In order to extend this to non-O157 EHEC serotypes, we examined the serological cross reactivity of TTSPs of serotypes O26:H11, O103:H2, O111:NM and O157:H7. Western blotting experiments with polyclonal antisera directed against serotype O157:H7 TTSPs suggested that there was significant cross reactivity, although there was limited cross reactivity when two Tir- and EspA-specific monoclonal antibodies were used. Groups of cattle were then vaccinated with TTSPs produced from each of the above serotypes and the magnitude and specificity of the responses were measured. All animals responded well with antibodies to TTSPs of the homologous serotype. However, limited cross reactivity was observed against the others. No cross reactivity was observed against Tir and EspA of serotype O157:H7. These results suggest that vaccination of cattle with TTSPs as a means of reducing the risk of EHEC transmission to humans will induce protection that is serotype specific.     

Verocytotoxin-producing Escherichia coli in foodstuffs of animal origin

While much research effort has been targeted at the verocytotoxin-producing Escherichia coli (VTEC) serotype O157:H7, it is becoming more evident that other VTEC serotypes can also be associated with human foodborne disease. An increasing number of these non-O157 serotypes have been isolated from food sources and from humans suffering from haemolytic-uraemic syndrome and diarrhoea. The aim of our work was to investigate the prevalence of VTEC O157 and non-O157 in foodstuffs of animal origin using two rapid enzymatic procedures. Various types of food samples, 352 in total, were tested: 233 with the Premier EHEC, a screening test which directly detects the presence of verocytotoxin, regardless of serotype, while 119 of these with the Vidas ECO, which is a specific screening test for E. coli O157:H7, together with the Premier EHEC. Two samples were positive for VTEC, one of serogroup O126 and the other was non-serotypable. Another sample was positive in the test specific for E. coli O157:H7, but was not confirmed by culture. This study suggests that VTEC strains are not prevalent in Italy, and that the isolation of serogroup O157 is relatively infrequent. This leads us to conclude that there is little chance of exposure to pathogen for the average consumer in Italy.     

Human infections with non-O157 Shiga toxin-producing Escherichia coli, Switzerland, 2000-2009

We characterized 97 non-O157 Shiga toxin (stx)-producing Escherichia coli strains isolated from human patients during 2000-2009 from the national reference laboratory in Switzerland. These strains belonged to 40 O:H serotypes; 4 serotypes (O26:H11/H-, O103:H2, O121:H19, and O145:H28/H-) accounted for 46.4% of the strains. Nonbloody diarrhea was reported by 23.2% of the patients, bloody diarrhea by 56.8%. Hemolytic uremic syndrome developed in 40.0% of patients; serotype O26:H11/H- was most often associated with this syndrome. Forty-five (46.4%) strains carried stx2 genes only, 36 strains (37.1%) carried stx1, and 16 (16.5%) strains carried stx1 and stx2. Genes encoding enterohemolysin and intimin were detected in 75.3% and 70.1% of the strains, respectively. Resistance to ≥1 antimicrobial agent was present in 25 isolates. High genetic diversity within strains indicates that non-O157 stx-producing E. coli infections in Switzerland most often occurred as single cases.     

副溶血性弧菌160株血清群型分布和耐药性分析

[目的]了解上海市浦东新区副溶血性弧菌群型分布及耐药情况。[方法]采用血清玻片凝集试验对160株副溶血性弧菌进行血清分型;采用改良K-B法进行耐药性测定。[结果]59株食物中毒分离株完全分型56株,分型率为94.92%,共分出7种血清型,O3∶K6(77.97%)居首位。101株水产品分离株完全分型32株,分型率为31.68%,共分出22种血清型,无优势血清型。药敏试验显示,副溶血性弧菌对氨苄西林高度耐药,对阿莫西林/克拉维酸、头孢吡肟、头孢噻肟、头孢他啶、氯霉素100.00%敏感。[结论]O3∶K6型是引起本区副溶血性弧菌食物中毒的主要血清型;水产品分离株血清型呈多样性,与食物中毒分离株不一致。本地区副溶血性弧菌没有产生广泛的耐药性变异。     

Serotypes of CNF1-producingEscherichia coli strains that cause extraintestinal infections in humans

The O:K:H serotypes of 137 necrotoxigenicEscherichia coli (NTEC) producing the cytotoxic necrotizing factor type 1 (CNF1) isolated from human extraintestinal infection were determined. Although NTEC producing CNF1 belonged to 58 different serotypes, only 10 of them accounted for 54% of strains. The most common serotypes, in order of frequency, were: O4:K?:H5, O6:K13:H1, O83:K1:H31, O75:K95:H5, O2:K1:H6, O2:K7:H-, O75:K1:H7, O2:K?:H1, O4:K12:H1 and O22:K13:H1. CNF1 strains of serotypes O2:K7:H- and O4:K12:H1 express P-fimbriae, whereas CNF1 strains of serotypes O2:K?:H1, O2:K1:H6 and O75:K95:H5 possess the adhesin responsible for MRHA type III. Among CNF1 strains of serotype O4:K?:H5 there exist some that express P-fimbriae and others that possess MRHA type III. Lastly, the majority of CNF1 strains of serotypes O6:K13:H1, O22:K13:H1, O75:K1:H7 and O83:K1:H31 do not express P-fimbriae nor the adhesin responsible to MRHA type III. Our results show that extraintestinal infections are caused by a limited number of virulent clones, as suggested by the theory of special pathogenicity.     

Persistence of Escherichia coli O157:H7 in dairy cattle and the dairy farm environment.

The persistence of Escherichia coli O157:H7 in cattle and the farm environment was investigated on eight Ontario dairy farms positive for E. coli O157:H7 in a longitudinal study commenced one year previously. Faecal samples from cows, calves, humans, cats, rodents, wild birds, a composite fly sample and numerous composite and individual environmental samples were cultured and tested for verotoxin-producing E. coli (VTEC). VTEC isolates were serotyped and E. coli O157:H7 isolates were phage typed. E. coli O157:H7 phage type 34 was isolated from one calf on each of two farms. The same phage type had been isolated on one of these farms 12 months earlier. Most E. coli O157:H7-positive animals and farms became culture-negative within 2 and 3 months, respectively. E. coli O157:H7 was not isolated from any environmental samples, although evidence of VTEC was found in composite samples from calf feeders (19.1%), calf barn surfaces (18%), cow feeders (14.9%), flies (12.5%), cow barn surfaces (11.3%), and individual milk filters (12.5%). VTEC belonging to 21 non-O157 serotypes were isolated from 24 cows (8.2%), 21 calves (18.3%), 2 cow feeder samples (3.0%), and 1 calf feeder sample (4.8%). Shedding of E. coli O157:H7 by infected dairy cattle appears to be transient and persistence of E. coli O157:H7 was not demonstrated from the farm environment sites tested.     

Human health impact of Salmonella contamination in imported soybean products: a semiquantitative risk assessment

The objectives of our study were to estimate the number of reported cases of human salmonellosis in Denmark that can be attributed to the occurrence of Salmonella in soy-based animal feed and to assess whether certain serotypes can be considered of less importance to human health. The assessment was based on a comparison of Salmonella serotypes isolated from feedstuffs, swine, cattle, and humans, primarily collected through the Danish Salmonella surveillance programs, supplemented with international data sources. The results are presented in three different forms: a qualitative assessment of all serotypes isolated from animal feed and/or food-producing animals based on their detection in humans; a semiquantitative ranking of serotypes by the apparent differences in their public health impact; and an estimate of the number of reported cases of human salmonellosis that can be attributed to the occurrence of Salmonella in soy-based animal feed. Salmonella isolates included in this study belonged to 91 distinct serotypes. Of the 82 serotypes found in both production animals and humans, 45 were also found in feed. In the period from 1999 to 2003, 14.4% of reported human infections were caused by serotypes also isolated from animal feed. Based on a modified version of a previously published risk model, we estimated that up to 1.7% of the total number of reported human cases and 2.1% of domestically acquired infections in the period 1999-2003 could be attributed to feedborne serotypes acquired through the consumption of Danish pork and beef. We concluded that more than 90% of serotypes have the potential, if they occur in feedstuffs, for infecting humans via production animals or foods of animal origin.     

Correlation between uropathogenic properties of Escherichia coli from urinary tract infections and the antibody-coated bacteria test and comparison with faecal strains.

Strains of Escherichia coli isolated from adult females with symptomatic urinary tract infection were found to possess the following properties significantly more frequently than faecal strains: (i) high K-antigen titre: (ii) haemolysin; (iii) type 1 pili; (iv) mannose-resistant haemagglutination; (v) fermentation of dulcitol and salicin; (vi) O serotype 2, 6 and 75; (vii) H serotype 1. E. coli isolated form urine specimens containing significant numbers of antibody-coated bacteria were richer in these seven properties than strains from urines without detectable antibody coated bacteria. The O and H serotypes of E. coli obtained from patients with urinary tract infection in two New Zealand cities were compared with those reported in the world literature and found to be similar.     

The enterotoxigenicity of strains of Escherichia coli isolated from the faeces of healthy people and cattle.

In this study 197 strains of Escherichia coli isolated from cowpats and the faeces of healthy humans were examined for the presence of enterotoxins. Six strains representing five different serotypes were found to be enterotoxigenic. Four of these strains produced the heat labile enterotoxin and two, the Vero cell cytotoxin.     

The distribution of Bacteroides fragilis serotypes amongst clinical strains.

Three hundred and twenty-two strains of Bacteroides fragilis isolated from infected patients at three different hospitals were tested against 20 type specific B. fragilis antisera using the tube agglutination technique. Of these strains 41.3% were assigned to a single O-serotype, a further 20.5% were agglutinated by several antisera and could not be classified and the remainder showed no reactions. Three different serotypes were prevalent in the three hospitals and minor geographical variation was observed. No correlation was found between serotypes and the origin of infection, but those from the blood were the most readily typable strains. No correlation was found between serotypes and biotypes of B. fragilis.