Sources of Fecal Pollution in Virginia’s Blackwater River

Sources of fecal pollution in the Blackwater River in south-central Virginia were identified. The study area encompassed intensive dairy and beef farming, abundant wildlife populations, homes with on-site septic systems, and four stream segments listed as impaired due to high-fecal coliform concentrations. A library of antibiotic resistance profiles was developed for 1,451 Enterococcus isolates from human, wildlife, and livestock. A discriminant analysis model was used to classify the isolates by source and calculate rates of correct classification (RCC) for each source. RCCs for the known source library were 82.3% for human, 86.2% for livestock, and 87.4% for wildlife. Profiles were determined for Enterococcus isolates from stream samples collected periodically from August 1999 to August 2001 (a total of 8,542 isolates) and compared against the known source library. Livestock contributed the highest percentage of isolates (47.6%) in the four segments studied, followed by wildlife (29.1%), and human (24.9%). The results indicate that reducing fecal pollution will require consideration of all three source categories. The results from this research are being used to develop total maximum daily load project allocations for fecal coliforms in the Blackwater River.     

Isolation of fecal coliform bacteria from the diamondback terrapin (Malaclemys terrapin centrata)

Total and fecal coliform bacteria were isolated from the cloaca and feces of the estuarine diamondback terrapin. The majority of samples contained fecal coliforms. Escherichia coli was the predominant fecal coliform species isolated, and members of the genus Salmonella were isolated from 2 of 39 terrapins. Fecal coliform numbers are used to regulate shellfish harvests, and diamondback terrapins inhabit the brackish-water habitats where oyster beds are found; therefore, these findings have implications for the efficacy of current regulatory parameters in shellfishing waters.     

Use of Total Coliform Test for Watershed Monitoring with Respect to Atypicals

A 2-year study was conducted on the relationships between atypical colonies (AC) from total coliform (TC) tests and other bacterial indicators of water quality in a watershed mainly impacted by agricultural and urban animals. Eight representative sites were monitored for TC, feel coliforms (FC) and coliphage (CP) concentrations. Sampling sites included those impacted by raw sewage, agricultural runoff, urban runoff, and a mixture of urban and agricultural runoff. AC were found to be composed of coliforms (about 27%), noncoliforms (37%), and Aeromonas (36%). There was a clear pattern among the atypical concentrations, fecal pollution sources, and pollution levels. Correlation analyses found the densities of AC to be well associated with the densities of FC and not well associated with total CP (RFC = 0.796 and RCP = 0.575, respectively). A reference index defined as the ratio of AC to CP correlated well with degree of fecal pollution known to impact the sites. Results suggest that AC from TC tests using the membrane filter method and M-Endo medium may be used as supplemental indicators in conjunction with other microbial indicators for watershed monitoring.     

Semiautomated microtiter plate assay for monitoring peptidylprolyl cis/trans isomerase activity in normal and pathological human sera

Elements mediating VanA glycopeptide resistance in 106 diverse enterococci from humans and nonhuman sources were compared with the prototype VanA transposon, Tn1546, in Enterococcus faecium BM4147. The isolates included 64 from individual patients at 15 hospitals in the United Kingdom (isolated between 1987 and 1996) and 42 from nonhuman sources in the United Kingdom (27 from raw meat, 7 from animal feces, and 8 from sewage). VanA elements were assigned to 24 groups (designated groups A to X) with primers that amplified 10 overlapping fragments of Tn1546. Ten groups of elements were found only in human enterococci, eight groups of elements were unique to nonhuman strains, and six groups of elements were common in enterococci from all sources. Elements indistinguishable from Tn1546 (group A) were observed more frequently in enterococci from nonhuman sources (34 versus 9%) but were identified in enterococci that caused outbreaks in hospital patients between 1987 and 1995. The most common group found in human enterococci (group H; 33%) was rarely observed in enterococci from other sources (5%). Group H elements differed from Tn1546 in three regions and included a novel insertion sequence, designated IS1542, between orf2 and vanR. The VanA elements of 14 other groups had a similar insertion at this position and/or distinct insertions at other positions. We conclude that VanA elements in enterococci are heterogeneous, although all show regions of homology with Tn1546. Furthermore, the elements most common among the human and nonhuman enterococci studied were different. This approach may be useful for monitoring the evolution of VanA resistance and may also be applicable in local "snapshot" epidemiological studies. However, as transposition events involving insertion sequences accounted for the differences observed between several groups, the stability of the elements must be assessed before their true epidemiological significance can be determined.     

Microcosm enrichment of biphenyl-degrading microbial communities from soils and sediments

A microcosm enrichment approach was employed to isolate bacteria which are representative of long-term biphenyl-adapted microbial communities. Growth of microorganisms was stimulated by incubating soil and sediment samples from polluted and nonpolluted sites with biphenyl crystals. After 6 months, stable population densities between 8 x 10(9) and 2 x 10(11) CFU/ml were established in the microcosms, and a large percentage of the organisms were able to grow on biphenyl-containing minimal medium plates. A total of 177 biphenyl-degrading strains were subsequently isolated and characterized by their ability to grow on biphenyl in liquid culture and to accumulate a yellow meta cleavage product when they were sprayed with dihydroxybiphenyl. Isolates were identified by using a polyphasic approach, including fatty acid methyl ester (FAME) analysis, 16S rRNA gene sequence comparison, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins, and genomic fingerprinting based on sequence variability in the 16S-23S ribosomal DNA intergenic spacer region. In all of the microcosms, isolates identified as Rhodococcus opacus dominated the cultivable microbial community, comprising a cluster of 137 isolates with very similar FAME profiles (Euclidean distances, <10) and identical 16S rRNA gene sequences. The R. opacus isolates from the different microcosms studied could not be distinguished from each other by any of the fingerprint methods used. In addition, three other FAME clusters were found in one or two of the microcosms analyzed; these clusters could be assigned to Alcaligenes sp., Terrabacter sp., and Bacillus thuringiensis on the basis of their FAME profiles and/or comparisons of the 16S rRNA gene sequences of representatives. Thus, the microcosm enrichments were strongly dominated by gram-positive bacteria, especially the species R. opacus, independent of the pollution history of the original sample. R. opacus, therefore, is a promising candidate for development of effective long-term inocula for polychlorinated biphenyl bioremediation.     

Microbiological quality of frozen fried chicekn product obtained from a retail store

Two brands of frozen fried chicken products were purchased monthly from a local supermarket for six months. Microbiological qualities of these samples were studied. The log number of mesophilic counts ranged from 2.90/g. to 4.78/g; log psychrophilic counts varied from 2.74/g. to 4.66/g.; and log Staphylococcus- 110 medium counts ranged from 2.84/g. to 4.54/g. Mean log microbial counts were higher in brand A samples than in brand B samples. No yeast or mold was detected and all samples were Salmonella negative. Most samples were negative in coliform test, except five samples had coliform MPN ranging from 0.5/g to 0.8/g. A total of 144 isolates of psychrophiles from 12 samples was tentatively identified to be members of Staphylococcus species. About 82.2% of the isolates belong to the Subgroup VI Staphylococcus according to Baird-Parker's classification. Another 17.8% of the isolates resembled Subgroup vi Staphylococcus except in phosphatase test.     

The use of microbiology in the study of hygiene behaviour

Faecal indicator bacteria have been used to measure levels of hygiene in a variety of settings. This paper describes a study in northern Botswana which used the isolation of faecal indicator bacteria in combination with other quantitative and qualitative techniques to gain information regarding hygiene behaviour. The microbiological samples included, samples from stored drinking water and water sources; eating plates; infant feeding bottles; dishcloths and the fingertips of carers and children. Water was usually clean at source but contaminated after storage. Presumptive faecal coliforms contaminated 31% of the eating plates, 29% of the dishcloths and 40% of the infant feeding bottles. Many of the presumptive faecal coliform isolates were not identified as Escherichia coli, indicating the need for further research into methodologies appropriate for isolating E. coli in tropical climates.     

Viral pollution in the environment and in shellfish: human adenovirus detection by PCR as an index of human viruses

A study of the presence of human viruses (adenoviruses, enteroviruses, and hepatitis A viruses [HAVs]) in environmental and shellfish samples was carried out by applying DNA and cDNA amplification techniques by PCR. The detection of human adenoviruses by PCR was also examined as a potential molecular test to monitor viral pollution. The samples studied were urban and slaughterhouse sewage, river water, seawater, and shellfish. Enteroviruses were quantified by PFU in Buffalo green monkey kidney cells and fecal coliforms and phages of Bacteroides fragilis HSP40 were also evaluated in some of the samples. The amplification of viral DNA and cDNA has shown a high prevalence of human viruses that would not be detected by the use of classical techniques, such as the quantification of PFU in cell lines. The results of the analysis of slaughterhouse sewage samples together with the test of farm animal feces indicate that the adenoviruses and the HAVs detected in the environment are mostly of human origin. A significative correlation between the detection of human viruses by PCR and the values of bacteriophages of B. fragilis HSP40 in urban raw sewage was observed. Human adenoviruses were the viruses most frequently detected throughout the year, and all the samples that were positive for enteroviruses or HAVs were also positive for human adenoviruses. The results suggest that the detection of adenoviruses by PCR could be used as an index of the presence of human viruses in the environment where a molecular index is acceptable.     

Composition and diversity of intestinal coliform flora influence bacterial translocation in rats after hemorrhagic stress

Coliform bacteria are the most frequently reported bacteria to translocate after hemorrhage. We investigated the correlation between composition and diversity of the cecal coliform flora and the degree of translocation in a rat model of hemorrhagic stress. Two groups of nine rats each were bled to 60 and 50 mm Hg mean arterial blood pressure, respectively. A sham-operated group without bleeding (n = 9) and a noninstrumented group (n = 6) served as controls. From each rat, 40 coliform isolates from the cecum and up to 16 from positive mesenteric lymph node (MLN) cultures were tested with an automated biochemical fingerprinting method. The phenotypic diversity of coliforms in each cecal sample was calculated as Simpson's diversity index (DI), and similarities between bacterial types in different samples were calculated as population similarity coefficients. Three rats in the sham-operated group and seven in each of the bled groups showed bacterial translocation. Of the different biochemical phenotypes (BPTs) found in the cecum of bled rats (mean, 6.5 BPTs), only a few were detected in MLNs (mean, 1.9 BPTs per MLN), with Escherichia coli being the dominant species. The translocating E. coli strains were mainly of two BPTs. Rats showing no translocation either did not carry these strains or had a high diversity of coliforms in the cecum. Furthermore, translocation of these coliform types was independent of their proportion in the cecum. In bled rats, the diversity of coliforms (mean DI, 0.53) was significantly higher than that in control groups (mean DI, 0.30; P = 0.004), suggesting that hemorrhage stimulates an increase in diversity of cecal coliforms. Rats with similar coliform flora and subjected to the same treatment showed similar patterns of translocation. Our results suggest that the composition of the coliform flora is an important factor in translocation and that certain coliform strains have the ability to translocate and survive in MLNs more easily than others.     

Total Coliform Survival Characteristics in Frozen Soils

Survival characteristics of total coliform bacteria in soil samples, with different moisture contents (24–49%) and at different temperatures (from ?28 to 20°C), were studied. The study showed that a significant fraction of coliform bacteria survive for more than six months in soil at subfreezing temperatures. Survival of total coliform bacteria at subfreezing temperatures decreased with an increase in moisture content and an increase in temperature. For 24% moisture, approximately 66% of the coliforms survived at ?28°C after 170 days, whereas less than 0.1% survived at room temperature. First-order die-off rate constants varied between 0.041/day at room temperature and 0.002/day from ?15 to ?28°C (for 24% moisture). The impact of temperature on the die-off rate constant was described by the Arrhenius equation. The high survival at subfreezing temperatures indicates that fecal bacteria at honeybucket dumpsites may survive throughout the Alaskan winter which may lead to the contamination of water sources during spring thaw.     

Relevance of abattoir hygiene assessment to microbial contamination of British beef carcases

Eleven beef abattoirs were visited, each on five separate occasions. On each occasion, an audit was carried out according to the official Hygiene Assessment System (HAS) and 10 carcases were sampled at four different sites to assess total viable counts and counts of presumptive coliform bacteria. The HAS scores ranged from 11 to 84 (maximum 100), and the logarithmic mean total viable counts for all sampling sites on each batch of carcases varied between 1.98 and 4.14 colony forming units/cm2. The mean prevalence of coliform contamination ranged from 0 to 85 per cent. There was a significant negative correlation (P < 0.001) between the mean HAS scores and the mean total viable count for each abattoir, but not between the HAS scores and the numbers of coliforms. Within the HAS, the mean scores for all five categories, before weighting, showed a significant correlation with the mean total viable count (P < 0.001); however, the categories concerned with slaughter and dressing, and personnel and practices were of most value in determining trends in carcase contamination. A new advisory classification is proposed for levels of microbial contamination on beef carcases.     

Application of polymerase chain reaction for the correlation of Salmonella serovars recovered from greyhound feces with their diet

The polymerase chain reaction was employed to correlate Salmonella serovars isolated from fecal material of greyhounds suffering from gastroenteritis with those isolated from the diet fed to the greyhounds prior to onset of diarrhea. Kennels around the Abilene, Kansas, area were contacted and supplied with materials needed to collect a portion of the diet each day. With the onset of diarrhea, the kennels were instructed to ship the fecal material and diet from the previous 10 days to the laboratory for testing. Forty-one fecal samples and corresponding diets were screened for Salmonella, Clostridium perfringens, Campylobacter jejuni, Staphylococcus aureus, Staphylococcus intermedius, and pathogenic (piliated) Escherichia coli by direct culture using standard procedures. The fecal material was also screened for coronavirus and parvovirus using electron microscopy. Thirty-five "normal" fecal samples were screened for all of the above mentioned microorganisms as a control. In addition, the fecal material was screened for E. coli verotoxins I and II and clostridial enterotoxins. A total of 61 Salmonella isolates were recovered from the 41 samples of feces and diet submitted for testing; 31 were recovered from the feces and 30 from the diet. Four Salmonella isolates were recovered from the normal fecal samples. Results obtained by PCR, plasmid profiles, antigenic analysis, and antibiogram profiles indicated that 16 of the 31 isolates recovered from the fecal material were the same strain as that recovered from the diet.     

Genetic and phenotypic diversity of 2,4-dichlorophenoxyacetic acid (2,4-D)-degrading bacteria isolated from 2,4-D-treated field soils

Forty-seven numerically dominant 2,4-dichlorophenoxyacetic acid (2,4-D)-degrading bacteria were isolated at different times from 1989 through 1992 from eight agricultural plots (3.6 by 9.1 m) which were either not treated with 2,4-D or treated with 2,4-D at three different concentrations. Isolates were obtained from the most dilute positive most-probable-number tubes inoculated with soil samples from the different plots on seven sampling dates over the 3-year period. The isolates were compared by using fatty acid methyl ester (FAME) profiles, chromosomal patterns obtained by PCR amplification of repetitive extragenic palindromic (REP) sequences, and hybridization patterns obtained with probes for the tfd genes of plasmid pJP4 and a probe (Spa probe) that detects a distinctly different 2,4-D-degrading isolate, Sphingomonas paucimobilis (formerly Pseudomonas paucimobilis). A total of 57% of the isolates were identified to the species level by the FAME analysis, and these isolates were strains of Sphingomonas, Pseudomonas, or Alcaligenes species. Hybridization analysis revealed four groups. Group I strains, which exhibited sequence homology with tfdA, -B, -C, and -D genes, were rather diverse, as determined by both the FAME analysis and the REP-PCR analysis. Group II, which exhibited homology only with the tfdA gene, was a small group and was probably a subset of group I. All group I and II strains had plasmids. Hybridization analysis revealed that the tfd genes were located on plasmids in 75% of these strains and on the chromosome or a large plasmid in the other 25% of the strains. One strain exhibited tfdA and -B hybridization associated with a plasmid band, while tfdC and -D hybridized with the chromosomal band area. The group III strains exhibited no detectable homology to tfd genes but hybridized to the Spa probe. The members of this group were tightly clustered as determined by both the FAME analysis and the REP-PCR analysis, were distinctly different from group I strains as determined by the FAME analysis, and had very few plasmids; this group contained more of the 47 isolates than any other group. The group III strains were identified as S. paucimobilis. The group IV strains, which hybridized to neither the tft prove nor the Spa probe, were as diverse as the group I strains as determined by the FAME and REP-PCR analyses. Most of group IV strains could not be identified by the FAME analysis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Full-scale studies of factors related to coliform regrowth in drinking water

An 18-month survey of 31 water systems in North America was conducted to determine the factors that contribute to the occurrence of coliform bacteria in drinking water. The survey included analysis of assimilable organic carbon (AOC), coliforms, disinfectant residuals, and operational parameters. Coliform bacteria were detected in 27.8% of the 2-week sampling periods and were associated with the following factors: filtration, temperature, disinfectant type and disinfectant level, AOC level, corrosion control, and operational characteristics. Four systems in the study that used unfiltered surface water accounted for 26.6% of the total number of bacterial samples collected but 64.3% (1,013 of 1,576) of the positive coliform samples. The occurrence of coliform bacteria was significantly higher when water temperatures were > 15 degrees C. For filtered systems that used free chlorine, 0.97% of 33,196 samples contained coliform bacteria, while 0.51% of 35,159 samples from chloraminated systems contained coliform bacteria. The average density of coliform bacteria was 35 times higher in free-chlorinated systems than in chloraminated water (0.60 CFU/100 ml for free-chlorinated water compared with 0.017 CFU/100 ml for chloraminated water). Systems that maintained dead-end free chlorine levels of < 0.2 mg/liter or monochloramine levels of < 0.5 mg/liter had substantially more coliform occurrences than systems that maintained higher disinfectant residuals. Free-chlorinated systems with AOC levels greater than 100 micrograms/liter had 82% more coliform-positive samples and 19 times higher coliform levels than free-chlorinated systems with average AOC levels less than 99 micrograms/liter. Systems that maintained a phosphate-based corrosion inhibitor and limited the amount of unlined cast iron pipe had fewer coliform bacteria. Several operational characteristics of the treatment process or the distribution system were also associated with increased rates of coliform occurrence. The study concludes that the occurrence of coliform bacteria within a distribution system is dependent upon a complex interaction of chemical, physical, operational, and engineering parameters. No one factor could account for all of the coliform occurrences, and one must consider all of the parameters described above in devising a solution to the regrowth problem.     

Case Study of a Marine Filter Curtain System for Coliform Reduction at a Public Beach

A floating marine filter curtain system (boom) was placed around a tidal beach on Long Island Sound to reduce coliform levels following storm events. Coliform data were collected inside and outside the boom over a three-year period. The results showed a 93% reduction in total coliforms and a 73% reduction in fecal coliforms, based on a comparison of the medians. Exceedences of the applicable water quality standards were reduced by 98% for total coliforms, and 81% for fecal coliforms. The method by which the boom actually reduces bacteria levels is thought to be a combination of filtration of solids, and the alteration of hydraulic conditions at the beach.     

Diabetes mellitus in sub-saharan Africa

The value of total coliforms, faecal coliforms and faecal streptococci in predicting the presence of Salmonella spp. and the numbers of Staphylococcus aureus and Candida albicans in sewage polluted coastal water were assessed. All indicators had strong positive association with Salmonella and moderate positive correlations with Staph. aureus and C. albicans. Total coliforms correlated better with salmonellas and Staph. aureus than did the two faecal groups. Regression analysis revealed that total coliforms have a better value as predictors of the presence of Salmonella and Staph. aureus, while faecal coliforms are better predictors of C. albicans, in moderately polluted areas. The conclusion reached is that enumeration of total coliforms is sufficient to predict the presence of Salmonella spp. or Staph. aureus in sea water moderately affected by sewage pollution, without the additional measurement of faecal coliforms and faecal streptococci.     

Coliform inhibition by bacteriocin-like substances in drinking water distribution systems

Bacterial isolates from an unchlorinated potable groundwater system and a chlorinated surface water system were screened by an agar overlay method for the ability to produce bacteriocin-like substances (BLS) inhibitory to the growth of Escherichia coli, Klebsiella sp., and Enterobacter aerogenes. The production of coliform-specific BLS by noncoliform bacteria varied with the site and date of isolation as well as the genus of the producer strain. A total of 448 bacterial isolates were screened from the chlorinated system, and 22.1% produced BLS specific for at least one of the three coliforms. In the unchlorinated system, 7.9% (n = 696) possessed this ability. Flavobacterium/Moraxella comprised 57.1% of all bacteria (from both systems) producing BLS. The possibility that BLS interfere with coliform detection in standard bacteriological water quality tests is discussed.     

Social isolation rearing: Species differences in behavior of macaque monkeys.

Social and nonsocial behaviors of 16 infant rhesus ( Macaca mulatta ) and 25 pigtail ( M. nemestrina ) monkeys reared in total social isolation were compared with those of 51 socialized controls. As a species, pigtail monkeys were more social, more passive, and less exploratory. Rhesus isolates exhibited a "typical" syndrome of abnormal behavior to a much greater extent than pigtail isolates. These results question the generality of rhesus total isolate behavior as a model for some human problems and illustrate the need to study many species, even among closely related nonhuman primates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The synaptic process in Locusta migratoria spermatocytes by synaptonemal complex analysis

BACKGROUND: Bacterial contamination of treated water and dialysate comprises an important problem for patients undergoing haemodialysis. Both the progressive reduction of the thickness of cellulose membranes and the expanding use of high-flux membranes probably enhance the risk of pyrogenic reactions, therefore increasing the need for atoxic water and non-pyrogenic dialysis fluid. METHODS: Samples of tap water, treated water, and effluent dialysate in all 85 haemodialysis centres in Greece were examined for total heterotrophic bacteria counts employing the pour plate method, total and faecal coliforms, faecal streptococci and pseudomonas spp. using the membrane filter technique, and sulphite-reducing clostridia applying the most probable number method. Overall 255 paired samples were tested from January to March 1997. RESULTS: For total heterotrophic bacteria, the overall compliance of treated water and dialysate to the American Association of Medical Instrumentation standards (<200 c.f.u./ml for water and <2000 c.f.u./ml for dialysate) was 92.6 and 63.7% respectively, whereas the compliance of tap water samples to our national standards (total heterotrophic bacteria < 10 c.f.u./ml and absence of the other indicator bacteria) was 80.7%. The most commonly isolated bacteria were pseudomonas spp., found in 22.2% of treated water and 59.5% of dialysate samples, whereas the respective frequencies were 12.3 and 36.2% for total coliforms, 8.6 and 30.0% for faecal coliforms, 14.8 and 28.7% for faecal streptococci, and sulphite-reducing clostridia were isolated in 5.8% of dialysate samples only. Haemodialysis centres equipped with storage tanks for treated water experienced lower levels of total heterotrophic bacteria, but higher counts of total and faecal coliforms, faecal streptococci, and pseudomonas spp., although the difference was statistically significant only for faecal streptococci counts, (P<0.05). Sixty-seven haemodialysis centres were equipped with bacterial filters, but mean values of all the examined microorganisms were not statistically different from those of the other centres. Faecal streptococci counts in treated water samples were positively correlated with ageing of both haemodialysis centres (P<0.005) and purification system (P<0.05), whereas pseudomonas counts were significantly correlated with ageing of the purification system (P<0.05).     

Association of enterohemorrhagic Escherichia coli hemolysin with serotypes of shiga-like-toxin-producing Escherichia coli of human and bovine origins

In this study we investigated whether the enterohemorrhagic Escherichia coli (EHEC) hemolysin gene ehxA could be used as an indicator of pathogenicity in Shiga-like-toxin-producing Escherichia coli (SLTEC) isolates. The isolates in a collection of 770 SLTEC strains of human and bovine origins were assigned to group 1 (230 human and 138 bovine SLTEC isolates belonging to serotypes frequently implicated in human disease), group 2 (85 human and 183 bovine isolates belonging to serotypes less frequently implicated in disease), and group 3 (134 bovine isolates belonging to serotypes not implicated in disease). PCR amplification was used to examine all of the SLTEC isolates for the presence of ehxA and the virulence-associated genes eae, slt-I, and slt-II. The percentages of human isolates in groups 1 and 2 that were positive for ehxA were 89 and 46%, respectively, and the percentages of bovine isolates in groups 1 to 3 that were positive for ehxA were 89, 51, and 52%, respectively. The percentages of human isolates in groups 1 and 2 that were positive for eae were 92 and 27%, respectively, and the percentages of bovine isolates in groups 1 to 3 that were positive for eae were 78, 15, and 19%, respectively. The frequencies of both ehxA and eae were significantly higher for group 1 isolates than for group 2 isolates. The presence of the ehxA gene was associated with serotype, as was the presence of the eae gene. Some serotypes, such as O117:H4, lacked both eae and ehxA and have been associated with severe disease, but only infrequently. The slt-I genes were more frequent in group 1 isolates than in group 2 isolates, and the slt-II genes were more frequent in group 2 isolates than in group 1 isolates. In a second experiment we determined the occurrence of the ehxA and slt genes in E. coli isolated from bovine feces. Fecal samples from 175 animals were streaked onto washed sheep erythrocyte agar plates. Eight E. coli-like colonies representing all of the morphological types were transferred to MacConkey agar. A total of 1, 080 E. coli isolates were examined, and the ehxA gene was detected in 12 independent strains, only 3 of which were positive for slt. We concluded that the ehxA gene was less correlated with virulence than the eae gene was and that EHEC hemolysin alone has limited value for screening bovine feces for pathogenic SLTEC because of presence of the ehxA gene in bovine isolates that are not SLTEC.