Massive outbreak of Escherichia coli O157:H7 infection in schoolchildren in Sakai City, Japan, associated with consumption of white radish sprouts

Global transcriptional response of Escherichia coli O157:H7 to growth transitions in glucose minimal medium

BACKGROUND

Global patterns of gene expression of Escherichia coli K-12 during growth transitions have been deeply investigated, however, comparable studies of E. coli O157:H7 have not been explored, particularly with respect to factors regulating virulence genes and genomic islands specific to this pathogen. To examine the impact of growth phase on the dynamics of the transcriptome, O157:H7 Sakai strain was cultured in MOPS minimal media (0.1% glucose), RNA harvested at 10 time points from early exponential to full stationary phase, and relative gene expression was measured by co-hybridization on high-density DNA microarrays. Expression levels of 14 genes, including those encoding Shiga toxins and other virulence factors associated with the locus of enterocyte effacement (LEE), were confirmed by Q-PCR.

RESULTS

Analysis of variance (R/MAANOVA, Fs test) identified 442 (36%) of 1239 O157-specific ORFs and 2110 (59%) of 3647 backbone ORFs that changed in expression significantly over time. QT cluster analysis placed 2468 of the 2552 significant ORFs into 12 groups; each group representing a distinct expression pattern. ORFs from the largest cluster (n = 1078) decreased in expression from late exponential to early stationary phase: most of these ORFs are involved in functions associated with steady state growth. Also represented in this cluster are ORFs of the TAI island, encoding tellurite resistance and urease activity, which decreased approximately 4-fold. Most ORFs of the LEE pathogenicity island also decreased approximately 2-fold by early stationary phase. The ORFs encoding proteins secreted via the LEE encoded type III secretion system, such as tccP and espJ, also decreased in expression from exponential to stationary phase. Three of the clusters (n = 154) comprised genes that are transiently upregulated at the transition into stationary phase and included genes involved in nutrient scavenging. Upregulated genes with an increase in mRNA levels from late exponential to early stationary phase belonged to one cluster (n = 923) which includes genes involved in stress responses (e.g. gadAB, osmBC, and dps). These transcript levels remained relatively high for > 3 h in stationary phase. The Shiga toxin genes (stx1AB and stx2B) were significantly induced after transition into stationary phase.

CONCLUSION

Expression of more than 300 O157-specific ORFs, many implicated in virulence of the O157 pathogen, was modulated in a growth dependent manner. These results provide a baseline transcriptional profile that can be compared to patterns of gene expression of this important foodborne pathogen under adverse environmental conditions.

Enhancement of Shiga toxin production in enterohemorrhagic Escherichia coli serotype O157:H7 by DNase colicins

Colicins are proteins produced by and active against several strains of Escherichia coli. Previously we reported that colicinogenic bacteria seemed beneficial in preventing the clinical manifestations of infectious disease caused by enterohemorrhagic E. coli O157 in humans. The inhibitory effects could be due to a decrease in O157 levels and/or pathogenicity. This study investigated the effects of colicinogenic E. coli on the production of Shiga toxin (Stx) by O157. Standard strains of colicinogenic bacteria carrying plasmids for each type of colicin (E3/5/8/9) were used for the study. The O157 strains were cultured in the presence of colicinogenic bacteria or extracted colicins. Compared with results for controls, DNase colicins (E8/9) facilitated an 8- to 64-fold increase in production of Stx2, while RNase colicins (E3/5) suppressed Stx production in only two strains. Stx prophages were induced in synchrony with Stx production. Semiquantitative real-time reverse transcription-PCR (RT-PCR) was then performed to examine SOS gene expression. The RT-PCR results clearly indicated a marked increase in mRNA levels of SOS reaction-associated genes after the addition of DNase colicins. We believe that Stx prophages are induced by the SOS response to DNA damage caused by DNase colicins, thus leading to higher Stx production. These findings suggest that while colicinogenic bacteria can be antagonistic to O157 infection, DNase colicins may enhance Stx production. Thus, colicinogenic flora is likely to be involved in the complex pathogenic pathways of O157 infection, and further investigation should be performed before the use of colicinogenic bacteria as an intervention method.

Combined effect of mild heat and acetic acid treatment for inactivating Escherichia coli O157:H7, Listeria monocytogenes and Salmonella typhimurium in an asparagus puree

AIMS

This study was conducted to validate combined heat and acid treatments for inactivating Escherichia coli O157:H7, Listeria monocytogenes and Salmonella typhimurium in an acidified brine containing, or pickled, asparagus model food.

METHODS AND RESULTS

A mixture of three strains of E. coli O157:H7, L. monocytogenes and S. typhimurium were inoculated onto pickled asparagus samples. Combinations of various concentrations of acetic acid [0%, 0.25%, 0.5%, 0.75%, 1%, 1.5% and 2% (v/v)] and various temperatures (40 degrees C, 50 degrees C, 60 degrees C and 75 degrees C) were investigated. Following treatment, asparagus samples were stored at room temperature and enumerated at 0, 0.5, 1, 2 and 3 days. Heat and acetic acid treatments were synergistic. The inhibitory effects of these combined treatments on the tested foodborne pathogens were also effective during storage. Loss of green colour in the pickled asparagus significantly increased with increasing concentrations of acetic acid.

CONCLUSIONS

Using a combination of mild heat and acetic acid treatments can successfully control E. coli O157:H7, L. monocytogenes and S. typhimurium in pickled asparagus, combinations of heat and acid are synergistic and effective treatments can be selected to reduce adverse effect on colour which occur during product storage.

SIGNIFICANCE AND IMPACT OF THE STUDY

Mild heating plus acetic acid treatment are synergistic, so combined treatments can be developed, which would lower the temperature and amount of acetic acid required for minimally processed vegetables while maintaining pathogen control.

Physiological and molecular responses of Lactuca sativa to colonization by Salmonella enterica serovar Dublin

This paper describes the physiological and molecular interactions between the human-pathogenic organism Salmonella enterica serovar Dublin and the commercially available mini Roman lettuce cv. Tamburo. The association of S. enterica serovar Dublin with lettuce plants was first determined, which indicated the presence of significant populations outside and inside the plants. The latter was evidenced from significant residual concentrations after highly efficient surface disinfection (99.81%) and fluorescence microscopy of S. enterica serovar Dublin in cross sections of lettuce at the root-shoot transition region. The plant biomass was reduced significantly compared to that of noncolonized plants upon colonization with S. enterica serovar Dublin. In addition to the physiological response, transcriptome analysis by cDNA amplified fragment length polymorphism analysis also provided clear differential gene expression profiles between noncolonized and colonized lettuce plants. From these, generally and differentially expressed genes were selected and identified by sequence analysis, followed by reverse transcription-PCR displaying the specific gene expression profiles in time. Functional grouping of the expressed genes indicated a correlation between colonization of the plants and an increase in expressed pathogenicity-related genes. This study indicates that lettuce plants respond to the presence of S. enterica serovar Dublin at physiological and molecular levels, as shown by the reduction in growth and the concurrent expression of pathogenicity-related genes. In addition, it was confirmed that Salmonella spp. can colonize the interior of lettuce plants, thus potentially imposing a human health risk when processed and consumed.

History of Public Health Crises in Japan

In Japan, a number of serious public health crises involving environmental pollution, food-borne diseases, and health hazards due to pharmaceuticals (i.e., "Yakugai") have occurred in the past 50 years. Based on the literature, we summarize the initial investigations and the subsequent measures. Some common points emerge: (1) prolonged cause identification, (2) lack of countermeasures after the cause was identified, and (3) discrimination against victims and they contributed to spreading the damage. We identify lack of corporate ethics and ill-timed disclosure of information as the principal problems in Japan's crisis-management systems. Defects in information gathering were common to all of the cases, thus we suggest necessary corrective measures, such as the establishment of a new reporting system for health hazard-related information.

An outbreak of Escherichia coli O157:H7 infection in southern Sweden associated with consumption of fermented sausage; aspects of sausage production that increase the risk of contamination

A large outbreak of enterohaemorrhagic Escherichia coli (EHEC) infections occurred in southern Sweden during autumn 2002. A matched case-control study was performed and indicated an association between consumption of fermented sausage and EHEC infection (odds ratio 5.4, P<0.002). Pulsed-field gel electrophoresis analysis identified a strain of E. coli O157:H7 in clinical faecal isolates, which was identical to a strain isolated from sausage samples obtained from households of infected individuals. A combination of microbiological and epidemiological results established a link between sausage consumption and the outbreak in 30 out of a total of 39 investigated cases. Contaminated beef was suspected to be the source of infection. Delayed start of fermentation, lack of heat-treatment and a short curing period in cold temperature were identified as the main factors enabling EHEC survival. EHEC can survive throughout the entire production process of fermented sausage if curing conditions are inadequate.

Neutralizing activity of bovine colostral antibody against verotoxin derived from enterohemorrhagic Escherichia coli O157:H7 in mice

The neutralization efficacy of bovine colostral antibody against verotoxin (VT) 1 and 2 was investigated. Cows were immunized with VT1 or VT2 fourteen times at 7-day intervals. A colostral antibody exhibiting high titers was obtained from immunized cows. Survival rates were evaluated in mice administered VT1 or VT2, and those infected with Escherichia coli (E. coli) O157:H7 producing VT1 or VT2. Survival rates after VT1 administration were 100% in the single-administration group, 90% in the repeat-administration group, and 78.6% in the control group. Survival rates after VT2 were 75.0% in the single-administration group, and 100% in the repeat-administration group. All mice in the control group died. Colostral antibody and fosfomycin (FOM) in the colostral antibody group and FOM and skim milk in the control group were administered three times per day for 5 days to mice infected with E. coli O157:H7 producing VT1 or VT2. Survival rates after inoculation with E. coli O157:H7 producing VT1 were 80.0% in the colostral antibody group, and 63.6% in the control group. Survival rates after inoculation with E. coli O157:H7 producing VT2 were 83.3% in the colostral antibody group, and 20.0% in the control group. The survival rate in mice without treatment following inoculation with E. coli O157:H7 producing VT2 was 88.2%. The survival rates in mice infected with E. coli O157:H7 strains producing VT1 or VT2 improved after administration of this colostral antibody, which exhibited neutralization efficacy against VT.

Emerging enterohaemorrhagic Escherichia coli, causes and effects of the rise of a human pathogen

Shiga toxin (Stx) [Verotoxin (VT)]-producing Escherichia coli (STEC), also called enterohaemorrhagic E. coli or VTEC are emerging zoonotic agents and became most important as human pathogens, particularly in the industrialized countries. Production of cytotoxins, also called Stx or VT, is the major pathogenicity determinant of STEC, which can cause life-threatening haemorrhagic diseases in humans. The spectrum of STEC phenotypes is diverse and domestic and wildlife animals constitute important reservoirs for these bacteria. STEC are spread from animal faeces to the environment, water and food. Ingestion of contaminated foodstuff and water, as well as contact with the environment, STEC-excreting animals or humans are the major sources of human infection. Economical changes in animal and food production, alteration of consumer habits and lack of specific immune response, particularly in urbanized populations, have contributed to the recent spread of STEC as a zoonotic agent. Supranational surveillance networks as well as national reference laboratories as sentinels play an important role in the prevention and control of STEC infections in humans. Development of new vaccines and probiotics may serve as future tools to control the spread of STEC in animals and humans.

An extensive repertoire of type III secretion effectors in Escherichia coli O157 and the role of lambdoid phages in their dissemination

Several pathogenic strains of Escherichia coli exploit type III secretion to inject "effector proteins" into human cells, which then subvert eukaryotic cell biology to the bacterium's advantage. We have exploited bioinformatics and experimental approaches to establish that the effector repertoire in the Sakai strain of enterohemorrhagic E. coli (EHEC) O157:H7 is much larger than previously thought. Homology searches led to the identification of >60 putative effector genes. Thirteen of these were judged to be likely pseudogenes, whereas 49 were judged to be potentially functional. In total, 39 proteins were confirmed experimentally as effectors: 31 through proteomics and 28 through translocation assays. At the protein level, the EHEC effector sequences fall into >20 families. The largest family, the NleG family, contains 14 members in the Sakai strain alone. EHEC also harbors functional homologs of effectors from plant pathogens (HopPtoH, HopW, AvrA) and from Shigella (OspD, OspE, OspG), and two additional members of the Map/IpgB family. Genes encoding proven or predicted effectors occur in >20 exchangeable effector loci scattered throughout the chromosome. Crucially, the majority of functional effector genes are encoded by nine exchangeable effector loci that lie within lambdoid prophages. Thus, type III secretion in E. coli is linked to a vast phage "metagenome," acting as a crucible for the evolution of pathogenicity.

Comparison of a PCR-restriction fragment length polymorphism (PCR-RFLP) assay to pulsed-field gel electrophoresis to determine the effect of repeated subculture and prolonged storage on RFLP patterns of Shiga toxin-producing Escherichia coli O157:H7

In this study, we compared a recently developed PCR-restriction fragment length polymorphism (PCR-RFLP) assay with pulsed-field gel electrophoresis (PFGE) using three different Shiga toxin-producing Escherichia coli (STEC) strains to understand whether repeated subculture in vitro and prolonged storage at room temperature affect the RFLP patterns of STEC. The PFGE profiles of the STEC strains changed by 1 to 8 fragments after repeated subculture and prolonged storage; one strain was no longer clonal after repeated subculture compared to the original isolate according to the Tenover criteria. In contrast, RFLP patterns obtained by PCR-RFLP were identical after repeated subculture and prolonged storage. These data clearly indicate that the PCR-RFLP assay which is based on the diversity of region V, a regulatory region of Stx-phage, was not affected by repeated subculture and prolonged storage and is a more practical and reliable method for molecular typing of STEC strains.

Role of Escherichia coli O157:H7 virulence factors in colonization at the bovine terminal rectal mucosa

The human pathogen Escherichia coli O157:H7 causes hemorrhagic colitis and life-threatening sequelae and transiently colonizes healthy cattle at the terminal rectal mucosa. This study analyzed virulence factors important for the clinical manifestations of human E. coli O157:H7 infection for their contribution to the persistence of E. coli in cattle. The colonizing ability of E. coli O157:H7 was compared with those of nonpathogenic E. coli K-12 and isogenic deletion mutants missing Shiga toxin (Stx), the adhesin intimin, its receptor Tir, hemolysin, or the approximately 92-kb pO157. Fully ruminant steers received a single rectal application of one E. coli strain so that effects of mucosal attachment and survival at the terminal rectum could be measured without the impact of bacterial passage through the entire gastrointestinal tract. Colonization was monitored by sensitive recto-anal junction mucosal swab culture. Nonpathogenic E. coli K-12 did not colonize as well as E. coli O157:H7 at the bovine terminal rectal mucosa. The E. coli O157:H7 best able to persist had intimin, Tir, and the pO157. Strains missing even one of these factors were recovered in lower numbers and were cleared faster than the wild type. In contrast, E. coli O157:H7 strains that were missing Stx or hemolysin colonized like the wild type. For these three strains, the number of bacteria increased between days 1 and 4 postapplication and then decreased slowly. In contrast, the numbers of noncolonizing strains (K-12, delta tir, and delta eae) decreased from the day of application. These patterns consistently predicted long-term colonization or clearance of the bacteria from the bovine terminal rectal mucosa.

Analysis of fimbrial gene clusters and their expression in enterohaemorrhagic Escherichia coli O157:H7

The sequence of two enterohaemorrhagic Escherichia coli (EHEC) O157:H7 strains reveals the possession of at least 16 fimbrial gene clusters, many of the chaperone/usher class. The first part of this study examined the distribution of these clusters in a selection of EHEC/EPEC (enteropathogenic E. coli) serotypes to determine if any were likely to be unique to E. coli O157:H7. Six of the clusters, as determined by the presence of amplified main subunit or usher gene sequences, were detected only in the E. coli O157 and O145 serotypes tested. With the exception of one serotype O103 strain that contained an lpf2 cluster, lpf sequences were only detected in E. coli O157 of the serotypes tested. Expression from each cluster was measured by the construction of chromosomally integrated lacZ promoter fusions and plasmid-based eGFP fusions in E. coli O157:H7. This analysis demonstrated that the majority (11/15) of main fimbrial subunit genes were not expressed under the majority of conditions tested in vitro. One of the clusters showing promoter activity, loc8, has a temperature expression optimum indicating a possible role outside the host. From the presence of pseudogenes in three of the clusters, the lack of FimH-like minor adhesins in the clusters and their limited expression in vitro, it would appear that E. coli O157:H7 has a limited repertoire of expressed functional fimbriae. This restricted selection of fimbriae may be important in bringing about the tropism E. coli O157:H7 demonstrates for the terminal rectum of cattle.

An outbreak of Escherichia coli O157 gastroenteritis in a care home for the elderly

In the summer of 2001 an outbreak of Escherichia coli O157 gastroenteritis affected staff and residents of a care home for the elderly in the West Midlands, UK. E. coli O157 phage type 2 was isolated from faeces in eight patients and 12 staff members. Thirty-five staff and 40 residents met the case definition for clinical gastrointestinal infection. Serological testing identified a further 14 possible cases of infection amongst asymptomatic staff and residents. The outbreak was atypical, as the disease seemed to be milder than has been observed in past outbreaks in similar settings. The index case, a member of staff, developed bloody diarrhoea and haemolytic-uraemic syndrome (HUS), but only one resident developed bloody diarrhoea and required hospitalization. No deaths occurred, despite the high-risk nature of the affected population. The source of the outbreak could not be identified. The prolonged nature of the outbreak and observed lapses in infection control practices indicated that person-to-person spread was the likely route of transmission. This outbreak illustrates the importance of observing appropriate infection control measures in the institutions providing residential and nursing care to the elderly.

Comparison of methods of extracting Salmonella enterica serovar Enteritidis DNA from environmental substrates and quantification of organisms by using a general internal procedural control

This paper compares five commercially available DNA extraction methods with respect to DNA extraction efficiency of Salmonella enterica serovar Enteritidis from soil, manure, and compost and uses an Escherichia coli strain harboring a plasmid expressing green fluorescent protein as a general internal procedural control. Inclusion of this general internal procedural control permitted more accurate quantification of extraction and amplification of S. enterica serovar Enteritidis in these samples and reduced the possibility of false negatives. With this protocol it was found that the optimal extraction method differed for soil (Mobio soil DNA extraction kit), manure (Bio101 soil DNA extraction kit), and compost (Mobio fecal DNA extraction kit). With each method, as little as 1.2 x 10(3) to 1.8 x 10(3) CFU of added serovar Enteritidis per 100 mg of substrate could be detected by direct DNA extraction and subsequent S. enterica-specific TaqMan PCR. After bacterial enrichment, as little as 1 CFU/100 mg of original substrate was detected. Finally, the study presents a more accurate molecular analysis for quantification of serovar Enteritidis initially present in soil or manure using DNA extraction and TaqMan PCR.

Pathogen detection, testing, and control in fresh broccoli sprouts

BACKGROUND

The recent increased interest in consuming green vegetable sprouts has been tempered by the fact that fresh sprouts can in some cases be vehicles for food-borne illnesses. They must be grown according to proper conditions of sanitation and handled as a food product rather than as an agricultural commodity. When sprouts are grown in accordance with the criteria proposed from within the sprout industry, developed by regulatory agencies, and adhered to by many sprouters, green sprouts can be produced with very low risk. Contamination may occur when these guidelines are not followed.

METHODS

A one year program of microbial hold-and-release testing, conducted in concert with strict seed and facility cleaning procedures by 13 U.S. broccoli sprout growers was evaluated. Microbial contamination tests were performed on 6839 drums of sprouts, equivalent to about 5 million consumer packages of fresh green sprouts.

RESULTS

Only 24 (0.75%) of the 3191 sprout samples gave an initial positive test for Escherichia coli O157:H7 or Salmonella spp., and when re-tested, 3 drums again tested positive. Composite testing (e.g., pooling up to 7 drums for pathogen testing) was equally sensitive to single drum testing.

CONCLUSION

By using a "test-and-re-test" protocol, growers were able to minimize crop destruction. By pooling drums for testing, they were also able to reduce testing costs which now represent a substantial portion of the costs associated with sprout growing. The test-and-hold scheme described herein allowed those few batches of contaminated sprouts to be found prior to packaging and shipping. These events were isolated, and only safe sprouts entered the food supply.

Evolution of foodborne pathogens via temperate bacteriophage-mediated gene transfer

Temperate bacteriophages have always been central to the evolution of bacteria, although their importance has been consistently underestimated compared to transformation and conjugation. In the last 20 years, as more gene and genome sequences have become available and researchers have more accurately determined bacteriophage populations in the environment, we are gaining a clearer picture of their role in the past and potential role in the future. The transductive and lysogenic capacities of this class of bacteriophages have contributed to the evolution and shaping of emerging foodborne pathogenic bacteria through the dissemination of virulence and antibiotic resistance genes. For example, the genome sequences of Shigella dysenteriae, Escherichia coli O157:H7, and the Stxencoding bacteriophages demonstrate the critical role bacteriophage-mediated gene transfer events played in the evolution of these high-profile human pathogens. In this review, we describe the basic genetic exchange mechanisms mediated by temperate bacteriophages and how these mechanisms have been central to the dissemination of virulence genes, such as toxins and antibiotics from one species to another (the shiga-like toxins, and multiple antibiotic resistance dissemination in Salmonella are used as specific examples). Data demonstrating the role of bacteriophages in the spread of antimicrobial resistance in bacteria, including interspecies transduction, are also presented. That temperate bacteriophages play a role in the on-going evolution of emerging pathogenic bacteria is obvious, but it is also clearly an on-going process with a breadth that must be appreciated as well as studied further if we are to be able to foresee what new challenges will arise to imperil food safety.

Efficiency of sodium hypochlorite, fumaric acid, and mild heat in killing native microflora and Escherichia coli O157:H7, Salmonella typhimurium DT104, and Staphylococcus aureus attached to fresh-cut lettuce

The effect of the disinfectant sodium hypochlorite (NaClO), with or without mild heat (50 degrees C) and fumaric acid, on native bacteria and the foodborne pathogens Staphylococcus aureus, Escherichia coli O157:H7, and Salmonella Typhimurium DT104 attached to iceberg lettuce leaves was examined. The retail lettuce examined consistently harbored 6 to 7 log CFU/g of native bacteria throughout the study period. Inner leaves supported 1 to 2 log CFU/g fewer bacteria than outer leaves. About 70% of the native bacterial flora was removed by washing five times with 0.85% NaCl. S. aureus, E. coli, and Salmonella allowed to attach to lettuce leaves for 5 min were more easily removed by washing than when allowed to attach for 1 h or 2 days, with more S. aureus being removed than E. coli or Salmonella Typhimurium. An increase of time for attachment of pathogens from 5 min to 2 days leads to decreased efficiency of the washing and sanitizing treatment. Treatment with fumaric acid (50 mM for 10 min at room temperature) was the most effective, although it caused browning of the lettuce, with up to a 2-log reduction observed. The combination of 200 ppm of sodium hypochlorite and mild heat treatment at 50 degrees C for 1 min reduced the pathogen populations by 94 to 98% (1.2- to 1.7-log reduction) without increasing browning.

Association between indicators of cattle density and incidence of paediatric haemolytic-uraemic syndrome (HUS) in children under 15 years of age in France between 1996 and 2001: an ecological study

Over the past years Shiga-like toxin-producing Escherichia coli (STEC) O157:H7 emerged as an important cause of severe gastrointestinal illnesses and haemolytic-uraemic syndrome (HUS) with up to 10% of children infected with STEC developing HUS. We conducted a geographical ecological study using the district as the statistical unit. For each district, we estimated the incidence of HUS among children <15 years for the period 1996-2001 from national HUS surveillance data and data obtained on cattle density. We used multivariate Poisson regression to quantify the relation, adjusted for covariates, between paediatric HUS incidence and exposure to cattle. In univariate analysis, a positive association was observed between several cattle-density indicators and HUS incidence. In multivariate analysis, HUS paediatric incidence was associated with dairy cattle density and the ratio of calves to children <15 years (P<0.001). Our findings are consistent with previous studies in other countries and support the recommendation to limit exposure of children to dairy cattle and manure to reduce the risk of STEC infection.

Adhesins of Enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) was first recognized as a cause of human disease in 1983 and is associated with diarrhea and hemorrhagic colitis, which may be complicated by life-threatening renal and neurological sequelae. EHEC are defined by their ability to produce one or more Shiga-like toxins (Stx), which mediate the systemic complications of EHEC infections, and to induce characteristic attaching and effacing lesions on intestinal epithelia, a phenotype that depends on the locus of enterocyte effacement. Acquisition of Stx-encoding bacteriophages by enteropathogenic E. coli is believed to have contributed to the evolution of EHEC, and consequently some virulence factors are conserved in both pathotypes. A key requirement for E. coli to colonize the intestines and produce disease is the ability to adhere to epithelial cells lining the gastrointestinal tract. Here, we review knowledge of the adhesins produced by EHEC and other Stx-producing E. coli, with emphasis on genetic, structural, and mechanistic aspects and their contribution to pathogenesis.

Risk of infection with Brucella abortus and Escherichia coli O157:H7 associated with marketing of unpasteurized milk in Kenya

As part of a study to assess zoonotic milk-borne health risks, seasonal survey data and unpasteurized milk samples were collected between January 1999 and February 2000 from randomly selected informal milk market agents (220 and 236 samples in the dry and wet seasons, respectively) and from households purchasing raw milk (213 and 219 samples in the dry and wet seasons, respectively) in rural and urban locations in central Kenya and screened for antibodies to Brucella abortus (B. abortus) and presence of Escherichia coli (E. coli) O157:H7. The latter was assessed based on samples from consumer households only. Antibodies to B. abortus were screened using the indirect antibody Enzyme Linked Immunosorbent Assay (ELISA) and the Milk Ring Test (MRT). The presence of E. coli O157:H7 was assessed by culture, biochemical characterisation, serological testing for production of verocytotoxin one (VT1) and two (VT2) and polymerase chain reaction (PCR) analysis for the presence of genes encoding for the toxins. The prevalence of antibodies to B. abortus varied considerably ranging from none in milk sold in small units and originating from intensive production systems to over 10% in samples that were bulked or originating from extensive production systems. E. coli O157:H7 was isolated from two samples (0.8%), one of which produced VT1. All urban consumers (100%) and nearly all rural consumers (96%) of marketed milk boiled the milk before consumption, mainly in tea, thus greatly reducing chances of exposure to live pathogens and potential health risks.

Use of the duplex TaqMan PCR system for detection of Shiga-like toxin-producing Escherichia coli O157

Real-time PCR assays have been applied for the detection and quantification of pathogens in recent years. In this study two combinations of primers and fluorescent probes were designed according to the sequences of the rfb(Escherichia coli O157) and stx2 genes. Analysis of 217 bacterial strains demonstrated that the duplex real-time PCR assay successfully distinguished the Escherichia coli O157 serotype from non-E. coli O157 serotypes and that it provided an accurate means of profiling the genes encoding O antigen and Shiga-like toxin 2. On the other hand, bacterial strains that lacked these genes were not detected by this assay. The quantitative ranges of the real-time PCR assay for these two genes were linear for DNA concentrations ranging from 10(3) to 10(9) CFU/ml of E. coli O157:H7 in pure culture and milk samples. The real-time PCR allowed the construction of standard curves that facilitated the quantification of E. coli O157:H7 in feces and apple juice samples. The detection sensitivity of the real-time PCR assay ranged from 10(4) to 10(9) CFU/g (or 10(4) to 10(9) CFU/ml) for feces and apple juice and 10(5) to 10(9) CFU/g for the beef sample without enrichment. After enrichment of the food samples in a modified tryptic soy broth, the detection range was from 10(0) to 10(3) CFU/ml. The real-time PCR assays for rfb(E. coli) (O157) and stx2 proved to be rapid tests for the detection of E. coli O157 in food matrices and could also be used for the quantification of E. coli O157 in foods or fecal samples.

Norovirus and foodborne disease, United States, 1991-2000

Analysis of foodborne outbreaks shows how advances in viral diagnostics are clarifying the causes of foodborne outbreaks and determining the high impact of norovirus infections.

Efforts to prevent foodborne illness target bacterial pathogens, yet noroviruses (NoV) are suspected to be the most common cause of gastroenteritis. New molecular assays allow for better estimation of the role of NoV in foodborne illness. We analyzed 8,271 foodborne outbreaks reported to the Centers for Disease Control and Prevention from 1991 to 2000 and additional data from 6 states. The proportion of NoV-confirmed outbreaks increased from 1% in 1991 to 12% in 2000. However, from 1998 to 2000, 76% of NoV outbreaks were reported by only 11 states. In 2000, an estimated 50% of foodborne outbreaks in 6 states were attributable to NoV. NoV outbreaks were larger than bacterial outbreaks (median persons affected: 25 versus 15), and 10% of affected persons sought medical care; 1% were hospitalized. More widespread use of molecular assays will permit better estimates of the role of NoV illness and help direct efforts to control foodborne illness.

Development of an immunomagnetic bead-immunoliposome fluorescence assay for rapid detection of Escherichia coli O157:H7 in aqueous samples and comparison of the assay with a standard microbiological method

The objective of this study was to develop and optimize a protocol for the rapid detection of Escherichia coli O157:H7 in aqueous samples by a combined immunomagnetic bead-immunoliposome (IMB/IL) fluorescence assay. The protocol consisted of the filtration or centrifugation of 30- to 100-ml samples followed by incubation of the filter membranes or pellet with anti-E. coli O157:H7 immunomagnetic beads in growth medium specific for E. coli O157:H7. The resulting E. coli O157:H7-immunomagnetic bead complexes were isolated by magnetic separation, washed, and incubated with sulforhodamine B-containing immunoliposomes specific for E. coli O157:H7; the final immunomagnetic bead-E. coli O157:H7-immunoliposome complexes were again isolated by magnetic separation, washed, and lysed with a n-octyl-beta-d-glucopyranoside to release sulforhodamine B. The final protocol took less than 8 h to complete and had a detection limit of less than 1 CFU of E. coli O157:H7 per ml in various aqueous matrices, including apple juice and cider. To validate the protocol at an independent facility, 100-ml samples of groundwater with and without E. coli O157:H7 (15 CFU) were analyzed by a public health laboratory using the optimized protocol and a standard microbiological method. While the IMB/IL fluorescence assay was able to identify E. coli O157:H7-containing samples with 100% accuracy, the standard microbiological method was unable to distinguish E. coli O157:H7-spiked samples from negative controls without further extensive workup. These results demonstrate the feasibility of using immunomagnetic beads in combination with sulforhodamine B-encapsulating immunoliposomes for the rapid detection of E. coli O157:H7 in aqueous samples.

Shiga-toxin-producing Escherichia coli and haemolytic uraemic syndrome

Most cases of diarrhoea-associated haemolytic uraemic syndrome (HUS) are caused by Shiga-toxin-producing bacteria; the pathophysiology differs from that of thrombotic thrombocytopenic purpura. Among Shiga-toxin-producing Escherichia coli (STEC), O157:H7 has the strongest association worldwide with HUS. Many different vehicles, in addition to the commonly suspected ground (minced) beef, can transmit this pathogen to people. Antibiotics, antimotility agents, narcotics, and non-steroidal anti-inflammatory drugs should not be given to acutely infected patients, and we advise hospital admission and administration of intravenous fluids. Management of HUS remains supportive; there are no specific therapies to ameliorate the course. The vascular injury leading to HUS is likely to be well under way by the time infected patients seek medical attention for diarrhoea. The best way to prevent HUS is to prevent primary infection with Shiga-toxin-producing bacteria.

Development of a PCR-restriction fragment length polymorphism assay for the epidemiological analysis of Shiga toxin-producing Escherichia coli

Six characteristic regions (I to VI) were identified in Shiga toxin 2 (Stx2) phages (T. Sato, T. Shimizu, M. Watarai, M. Kobayashi, S. Kano, T. Hamabata, Y. Takeda, and S. Yamasaki, Gene 309:35-48, 2003). Region V, which is ca. 10 kb in size and is located in the upstream region of the Stx operons, includes the most distinctive region among six Stx phages whose genome sequences have been determined. In this study, we developed a PCR-restriction fragment length polymorphism (RFLP) assay for the epidemiological analysis of Shiga toxin-producing Escherichia coli (STEC) on the basis of the diversity of region V. When region V was amplified by long and accurate-PCR (LA-PCR) with five control E. coli strains carrying six different Stx phages such as E. coli strains C600 (Stx1 phage), C600 (933W phage), C600 (Stx2 phage-I), C600 (Stx2 phage-II), and O157:H7 Sakai strain RIMD0509952 (VT1-Sakai phage and VT2-Sakai phage), an expected size of the band was obtained. Restriction digest of each PCR product with BglI or EcoRV also gave the expected sizes of banding patterns and discriminated the RFLPs of five control strains. When a total of 204 STEC O157 strains were analyzed by LA-PCR, one to three bands whose sizes ranged from 8.2 to 14 kb were obtained. Two STEC O157 strains, however, did not produce any bands. Subsequent restriction digest of the PCR products with BglI or EcoRV differentiated the RFLPs of 202 STEC O157 strains into 24 groups. The RFLP patterns of pulsed-field gel electrophoresis (PFGE) of representative strains of STEC O157 divided into 24 groups were well correlated with those of PCR-RFLP when STEC O157 strains were isolated in the same time period and in the close geographic area. To evaluate the PCR-RFLP assay developed here, ten strains, each isolated from four different outbreaks in different areas in Japan (Tochigi, Hyogo, Aichi, and Fukuoka prefecture), were examined to determine whether the strains in each group showed the same RFLP patterns in the PCR-RFLP assay. In accordance with the results of PFGE except for strains isolated in an area (Fukuoka), which did not produce any amplicon, ten strains in each group demonstrated the same RFLP pattern. Taken together, these data suggest that the PCR-RFLP based on region V is as useful as PFGE but perhaps more simple and rapid than PFGE for the molecular epidemiological analysis of STEC strains during sporadic and common source outbreaks.

The Shiga toxin-producing Escherichia coli, their ruminant hosts, and potential on-farm interventions: a review

The emergence of Shiga toxin-producing Escherichia coli serotype O157:H7 as a major human pathogen over the last 2 decades has focused attention on this organism’s ruminant hosts. Despite implementation of conventional control methods, people continue to become seriously ill from contaminated meat or other food products, manure-contaminated drinking and recreational water, and direct contact with ruminants. E. coli O157:H7 can cause life-threatening disease, and is a particular threat to children, through acute and chronic kidney damage. Compared with other food-borne bacteria, E. coli O157:H7 has a remarkably low infectious dose and is environmentally robust. Cattle are largely unaffected by this organism and have been identified as the major source of E. coli O157:H7 entering the human food chain. Other Shiga toxin-producing E. coli can be pathogenic to humans and there is increasing evidence that their significance has been underestimated. Governments around the world have acted to tighten food safety regulations, and to investigate animal sources and on-farm control of this and related organisms. Potential intervention strategies on-farm include: feed and water hygiene, altered feeding regimes, specific E. coli vaccines, antibacterials, antibiotics, probiotics, and biological agents or products such as bacteriophages, bacteriocins, or colicins.

Irrigation water as source of foodborne pathogens on fruit and vegetables

Awareness is growing that fresh or minimally processed fruit and vegetables can be sources of disease-causing bacteria, viruses, protozoa, and helminths. Irrigation with poor-quality water is one way that fruit and vegetables can become contaminated with foodborne pathogens. Groundwater, surface water, and human wastewater are commonly used for irrigation. The risk of disease transmission from pathogenic microorganisms present in irrigation water is influenced by the level of contamination; the persistence of pathogens in water, in soil, and on crops; and the route of exposure. Groundwater is generally of good microbial quality, unless it is contaminated with surface runoff; human wastewater is usually of very poor microbial quality and requires extensive treatment before it can be used safely to irrigate crops; surface water is of variable microbial quality. Bacteria and protozoa tend to show the poorest survival outside a human host, whereas viruses and helminths can remain infective for months to years. Guidelines governing irrigation water quality and strategies to reduce the risk of disease transmission by foodborne pathogens in irrigation are discussed.

Comparison of a membrane surface adhesion recovery method with an IMS method for use in a polymerase chain reaction method to detect Escherichia coli O157:H7 in minced beef

In this study, enrichment procedures and two recovery methods, a membrane surface adhesion technique and an immunomagnetic separation (IMS), were compared for use in conjunction with a multiplex polymerase chain reaction (PCR) method with a view to describing a fast (24 h) and economical test for detection of Escherichia coli O157:H7 in meat samples. The study showed no significant difference between three different enrichment media (BHI, E. coli (E.C.) broth+novobiocin, modified tryptone soya broth (mTSB)+novobiocin) or two incubation temperatures (37 or 41.5 degrees C) for growth of E. coli O157:H7 in minced beef. Minced beef samples inoculated with E. coli O157:H7 at 40 cfu g(-1) were incubated at 37 degrees C for 16 h in E.C. broth+novobiocin reaching numbers of (log(10)7.82-8.70). E. coli O157:H7 were recovered by attachment to polycarbonate membranes immersed in the enriched cultures for 15 min or by immunomagnetic separation. Subsequent treatment of recovered membranes or IMS beads with lysis buffer and phenol/chloroform/isoamyl alcohol was used to extract the DNA from the extracted E. coli O157:H7 cells. The results show when E. coli O157:H7 was present at high levels in the enriched meat sample (log(10)9.6-7.5 cfu ml(-1); >16-h enrichment), the membrane and IMS techniques recovered similar levels of the pathogen and the microorganism was detectable by PCR using both methods. At lower levels of E. coli O157:H7 (log(10)6.4), only the IMS method could recover the pathogen but at levels below this neither method could recover sufficient numbers of the pathogens to allow detection. The conclusion of the study is that with sufficient enrichment time (16 h) the membrane surface adhesion membrane extraction method used in combination with multiplex PCR has the potential for a rapid and economical detection method.

Identification of Escherichia coli O157 : H7 genes influencing colonization of the bovine gastrointestinal tract using signature-tagged mutagenesis

Enterohaemorrhagic Escherichia coli (EHEC) cause acute gastroenteritis in humans that may be complicated by life-threatening systemic sequelae. The predominant EHEC serotype affecting humans in the UK and North America is O157 : H7 and infections are frequently associated with contact with ruminant faeces. Strategies to reduce the carriage of EHEC in ruminants are expected to lower the incidence of human EHEC infections; however, the molecular mechanisms underlying persistence of EHEC in ruminants are poorly understood. This paper reports the first comprehensive survey for EHEC factors mediating colonization of the bovine intestines by using signature-tagged transposon mutagenesis. Seventy-nine E. coli O157 : H7 mutants impaired in their ability to colonize calves were isolated and 59 different genes required for intestinal colonization were identified by cloning and sequencing of the transposon insertion sites. Thirteen transposon insertions were clustered in the locus of enterocyte effacement (LEE), which encodes a type III protein secretion system required for the formation of attaching and effacing lesions on intestinal epithelia. A putative structural component of the apparatus (EscN) is essential for intestinal colonization; however, the type III secreted effector protein Map plays only a minor role. Other Type III secretion-associated genes were implicated in colonization of calves by E. coli O157 : H7, including z0990 (ecs0850), which encodes the non-LEE-encoded type III secreted effector NleD and the closely related z3023 (ecs2672) and z3026 (ecs2674) genes which encode homologues of Shigella IpaH proteins. We also identified a novel fimbrial locus required for intestinal colonization in calves by E. coli O157 : H7 (z2199-z2206; ecs2114-ecs2107/locus 8) and demonstrated that a mutant harbouring a deletion of the putative major fimbrial subunit gene is rapidly out-competed by the parent strain in co-infection studies. Our data provide valuable new information for the development of intervention strategies.

The effect of probiotic treatment with Clostridium butyricum on enterohemorrhagic Escherichia coli O157:H7 infection in mice

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 has been considered as an agent responsible for outbreak of hemorrhagic colitis and the hemolytic uremic syndrome. We examined the effect of the probiotic agent Clostridium butyricum MIYAIRI strain 588 on EHEC O157:H7 infections in vitro and in vivo using gnotobiotic mice. The growth of EHEC O157:H7 and the production of Shiga-like toxins in broth cultures were inhibited by co-incubation with C. butyricum. The antibacterial effects of butyric and lactic acid were demonstrated in a dose-dependent manner. In addition, the inhibitory effect of butyric acid on the viability of EHEC was demonstrated not only at low pH, but also at neutral pH adjusted to 7.0. Flowcytometric analysis showed that pre-incubation of Caco-2 cells with C. butyricum and E. coli K12 inhibited the adhesion of EHEC O157:H7. However, the effect of C. butyricum on adhesion of EHEC to Caco-2 cells was more inhibitory than that of E. coli K12. Gnotobiotic mice mono-associated with EHEC O157:H7 died within 4-7 days after the infection. On the other hand, all gnotobiotic mice prophylactically pre-treated with C. butyricum survived exposure to EHEC O157:H7 and of the gnotobiotic mice therapeutically post-treated with C. butyricum, 50% survived. Both counts of EHEC O157:H7 and the amounts of shiga-like toxins (Stx1 and Stx2) in fecal contents of gnotobiotic mice di-associated with EHEC O157:H7 and C. butyricum were less than those of gnotobiotic mice mono-associated with EHEC O157:H7. These results indicated that the probiotic bacterium C. butyricum MIYAIRI strain 588 has preventive and therapeutic effects on EHEC O157:H7 infection in gnotobiotic mice.

High prevalence of enterohemorrhagic Escherichia coli (EHEC) O157 from cattle in selected regions of Japan

The prevalence of enterohemorrhagic Escherichia coli (EHEC) O157 was examined in bovine faeces. EHEC O157 was isolated from the faeces of 42 (13.0%) of 324 cattle. Of the 4 farms and the facilities tested, the 3 farms and the facilities were found positive for EHEC O157. The highest isolation rate among the farms was 33.7%. The prevalence of EHEC O157 in heifers was higher than that in calves and other cattle. No cattle positive for EHEC O157 showed any clinical signs except 2 calves with diarrhea in a veterinary hospital. Almost all isolates possessed the stx gene, and Stx-positive strains carrying both stx(1) and stx(2) genes were predominant. These results indicate that EHEC O157 are distributed in bovine faeces, and that dairy and beef farms in selected regions of Japan are heavily contaminated with the organisms.

Acid resistance systems required for survival of Escherichia coli O157:H7 in the bovine gastrointestinal tract and in apple cider are different

Escherichia coli O157:H7 is a highly acid-resistant food-borne pathogen that survives in the bovine and human gastrointestinal tracts and in acidic foods such as apple cider. This property is thought to contribute to the low infectious dose of the organism. Three acid resistance (AR) systems are expressed in stationary-phase cells. AR system 1 is sigma(S) dependent, while AR systems 2 and 3 are glutamate and arginine dependent, respectively. In this study, we sought to determine which AR systems are important for survival in acidic foods and which are required for survival in the bovine intestinal tract. Wild-type and mutant E. coli O157:H7 strains deficient in AR system 1, 2, or 3 were challenged with apple cider and inoculated into calves. Wild-type cells, adapted at pH 5.5 in the absence of glucose (AR system 1 induced), survived well in apple cider. Conversely, the mutant deficient in AR system 1, shown previously to survive poorly in calves, was susceptible to apple cider (pH 3.5), and this sensitivity was shown to be caused by low pH. Interestingly, the AR system 2-deficient mutant survived in apple cider at high levels, but its shedding from calves was significantly decreased compared to that of wild-type cells. AR system 3-deficient cells survived well in both apple cider and calves. Taken together, these results indicate that E. coli O157:H7 utilizes different acid resistance systems based on the type of acidic environment encountered.

Frequency of Shiga toxin-producing Escherichia coli (STEC) isolates among diarrheic and non-diarrheic calves in Brazil

The occurrence of Shiga toxin (Stx) gene sequences was examined in 344 fecal samples from diarrheic (n=139) and non-diarrheic (n=205) calves from 12 beef farms in São Paulo State, Brazil to study the prevalence of Shiga toxin-producing Escherichia coli (STEC) strains. Forty-four (12.7%) animals were found to be positive for stx. The frequency of carriage of stx was higher in diarrheic calves (28/139, 20%) than in non-diarrheic animals (16/205, 7.8%) (P<0.001). Among the 24 STEC strains recovered from the animals, 12 isolates carried stx1, four stx2, and 8 carried both stx1 and stx2 genes. The eae and the enterohaemolysin (Ehly) gene sequences occurred at high frequencies in these STEC strains (41.6 and 50.0%, respectively). A total of 16 serotypes were identified. The serotypes O111:NM (four isolates), O111:H8 (two) and O118:H16 (one), currently described as enterohaemorrhagic E. coli (EHEC), were isolated from cattle in Brazil for the first time. These findings reinforce the importance of cattle as a reservoir of EHEC strains in Brazil.

Rapid detection of respiring Escherichia coli O157:H7 in apple juice, milk, and ground beef by flow cytometry

BACKGROUND

Rapid and simple methods to detect viable pathogenic microbes in foods and drinks are required. Flow cytometry was used for the rapid detection of respiring Escherichia coli O157:H7 cells in apple juice, milk, and ground beef.

METHODS

CTC (5-cyano-2,3-ditolyl tetrazolium chloride) was used to estimate the respiratory activity of bacteria. Fluorescein isothiocyanate (FITC)-labeled anti-E. coli O157:H7 direct antibody (FA) was used for the specific detection of target cells. Food samples were inoculated with starved E. coli O157:H7 and E. coli K-12 cells, and analyzed by both fluorescent microscopy and flow cytometry after double staining with FA and CTC.

RESULTS

Respiring E. coli O157:H7 cells in food samples showed strong fluorescence of both FA (green) and CTC (red); thus, they could be clearly and specifically distinguished from respiring E. coli K-12 or inactive cells. A good correlation was achieved in flow cytometric analysis between the numbers of inoculated viable E. coli O157:H7 and those detected in milk and apple juice. The detection threshold for this flow cytometry for E. coli O157:H7 in milk, apple juice, and ground beef was 10(3) cells/ml (milk and apple juice) or 10(3) cells/g (ground beef) of sample when the total bacterial number in the sample was 10(6) cells/ml.

CONCLUSIONS

Respiring E. coli O157:H7 in food samples can be detected specifically within a few hours. Flow cytometry with FA-CTC double staining can be used to examine food contamination with various pathogenic microbes demonstrating physiologic activity through the use of a suitable fluorescent antibody.

Acid tolerance and gad mRNA levels of Escherichia coli O157:H7 grown in foods

We examined the acid tolerance and gad mRNA levels of Escherichia coli O157:H7 (three strains) and nonpathogenic E. coli (strains K12, W1485, and B) grown in foods. The E. coli cells (approximately 30,000 cells) were inoculated on the surface of 10 g of solid food samples (asparagus, broccoli, carrot, celery, cucumber, eggplant, ginger, green pepper, onion, potato, radish, tomato and beef) and in 10 ml of cow's milk, cultured statically at 10-25 degrees C for 1-14 days, and subjected to an acid challenge at 37 degrees C for 1 h in LB medium (pH 3.0). When grown at 20 and 25 degrees C in all foods, except for tomato and ginger, the strains showed a stationary-phase specific acid tolerance. The acid tolerance of the O157 strains changed depending on the types of foods (3-10% survival), but was clearly lower than that of the cells grown in EC medium (more than 90% survival). Tomato and ginger induced relatively high acid tolerances (10-30% survival) in the O157 strains irrespective of the growth phase, probably because of their acidity. No remarkable difference was observed in the acid tolerance between the O157 and nonpathogenic strains grown in all foods. When grown at 10 and 15 degrees C in the foods and EC medium, none of the strains showed the stationary-phase specific acid tolerance. In beef, broccoli, celery, potato and radish, the acid tolerance showed a tendency to decrease with the prolonged cultivation time. In other foods, the acid tolerance was almost constant (about 0.1% survival) irrespective of the growth stage. The mRNA level of glutamate decarboxylase genes (gadA and gadB) correlated to the acid tolerance level when the E. coli cells were grown at 25 degrees C, but was very low even in the stationary phase when the E. coli cells were grown at 15 degrees C or below.

Rapid apoptosis induced by Shiga toxin in HeLa cells

Apoptosis was induced rapidly in HeLa cells after exposure to bacterial Shiga toxin (Stx1 and Stx2; 10 ng/ml). Approximately 60% of HeLa cells became apoptotic within 4 h as detected by DNA fragmentation, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assay, and electron microscopy. Stx1-induced apoptosis required enzymatic activity of the Stx1A subunit, and apoptosis was not induced by the Stx2B subunit alone or by the anti-globotriaosylceramide antibody. This activity was also inhibited by brefeldin A, indicating the need for toxin processing through the Golgi apparatus. The intracellular pathway leading to apoptosis was further defined. Exposure of HeLa cells to Stx1 activated caspases 3, 6, 8, and 9, as measured both by an enzymatic assay with synthetic substrates and by detection of proteolytically activated forms of these caspases by Western immunoblotting. Preincubation of HeLa cells with substrate inhibitors of caspases 3, 6, and 8 protected the cells against Stx1-dependent apoptosis. These results led to a more detailed examination of the mitochondrial pathway of apoptosis. Apoptosis induced by Stx1 was accompanied by damage to mitochondrial membranes, measured as a reduced mitochondrial membrane potential, and increased release of cytochrome c from mitochondria at 3 to 4 h. Bid, an endogenous protein known to permeabilize mitochondrial membranes, was activated in a Stx1-dependent manner. Caspase-8 is known to activate Bid, and a specific inhibitor of caspase-8 prevented the mitochondrial damage. Although these data suggested that caspase-8-mediated cleavage of Bid with release of cytochrome c from mitochondria and activation of caspase-9 were responsible for the apoptosis, preincubation of HeLa cells with a specific inhibitor of caspase-9 did not protect against apoptosis. These results were explained by the discovery of a simultaneous Stx1-dependent increase in endogenous XIAP, a direct inhibitor of caspase-9. We conclude that the primary pathway of Stx1-induced apoptosis and DNA fragmentation in HeLa cells is unique and includes caspases 8, 6, and 3 but is independent of events in the mitochondrial pathway.

Alfalfa seed decontamination in a Salmonella outbreak

Based on in vitro data, the U.S. Food and Drug Administration recommends chemical disinfection of raw sprout seeds to reduce enteric pathogens contaminating the seed coats. However, little is known about the effectiveness of decontamination at preventing human disease. In 1999, an outbreak of Salmonella enterica serotype Mbandaka occurred in Oregon, Washington, Idaho, and California. Based on epidemiologic and pulsed-field gel electrophoresis evidence from 87 confirmed cases, the outbreak was linked to contaminated alfalfa seeds grown in California's Imperial Valley. Trace-back and trace-forward investigations identified a single lot of seeds used by five sprout growers during the outbreak period. Cases of salmonellosis were linked with two sprout growers who had not employed chemical disinfection; no cases were linked to three sprout growers who used disinfection. This natural experiment provides empiric evidence that chemical disinfection can reduce the human risk for disease posed by contaminated seed sprouts.

An improved enrichment broth for isolation of Escherichia coli O157, with specific reference to starved cells, from radish sprouts

An enrichment broth was developed for the efficient isolation of Escherichia coli O157 from radish sprouts. The broth was buffered peptone water containing 0.5% sodium thioglycolate (STG-BPW), which was designed to allow growth of E. coli O157 in starved and unstarved states. However, this medium suppressed the growth of non-carbohydrate-fermenting obligate aerobes whose colonial appearance on sorbitol MacConkey agar containing cefixime and tellurite (CT-SMAC) resembled that of E. coli O157. Both starved and unstarved cells of E. coli O157 experimentally inoculated into radish sprouts were successfully recovered with STG-BPW enrichment in all cases, most of which showed marked disappearance of E. coli O157-like colonies on CT-SMAC.

Use of immunoglobulin enriched bovine colostrum against oral challenge with enterohaemorrhagic Escherichia coli O157:H7 in mice

An immunoglobulin enriched bovine colostrum preparation, IMMULAC (New Zealand Dairy Group, Cambridge, New Zealand), contains antibodies against various bacterial antigens. In the present study, we investigated the protective effects of a commercial bovine colostrum preparation against infections with enterohaemorrhagic Escherichia coli (EHEC) O157:H7 in a murine model. Balb/c mice were given drinking water containing streptomycin for 3 days before and following oral challenge with streptomycin-resistant EHEC O157:H7 strain (O157-SM(R)). In mice pretreated with streptomycin, EHEC O157:H7 maintained stable levels of bacterial colonization in the intestines for the 3-week experimental time period. Oral administration of colostrum resulted in rapid decrease in the bacteria numbers compared with administration of skim-milk. Colostrum showed no direct in vitro bactericidal properties against either EHEC O157:H7. When sections prepared from cecum walls of streptomycin-pretreated mice were incubated in vitro with EHEC O157:H7, the colostrum significantly prevented the attachment of the organisms to the sections when compared with skim-milk. These results indicate that oral administration of bovine colostrum effectively protects mice against food-borne infections by inhibiting bacterial attachment to the intestinal mucous membrane, colonization and growth in the intestinal tract.

Detection, isolation, and molecular subtyping of Escherichia coli O157:H7 and Campylobacter jejuni associated with a large waterborne outbreak

The largest reported outbreak of waterborne Escherichia coli O157:H7 in the United States occurred in upstate New York following a county fair in August 1999. Culture methods were used to isolate E. coli O157:H7 from specimens from 128 of 775 patients with suspected infections. Campylobacter jejuni was also isolated from stools of 44 persons who developed diarrheal illness after attending this fair. There was one case of a confirmed coinfection with E. coli O157:H7 and C. jejuni. Molecular detection of stx(1) and stx(2) Shiga toxin genes, immunomagnetic separation (IMS), and selective culture enrichment were utilized to detect and isolate E. coli O157:H7 from an unchlorinated well and its distribution points, a dry well, and a nearby septic tank. PCR for stx(1) and stx(2) was shown to provide a useful screen for toxin-producing E. coli O157:H7, and IMS subculture improved recovery. Pulsed-field gel electrophoresis (PFGE) was used to compare patient and environmental E. coli O157:H7 isolates. Among patient isolates, 117 of 128 (91.5%) were type 1 or 1a (three or fewer bands different). Among the water distribution system isolates, 13 of 19 (68%) were type 1 or 1a. Additionally, PFGE of C. jejuni isolates revealed that 29 of 35 (83%) had indistinguishable PFGE patterns. The PFGE results implicated the water distribution system as the main source of the E. coli O157:H7 outbreak. This investigation demonstrates the potential for outbreaks involving more than one pathogen and the importance of analyzing isolates from multiple patients and environmental samples to develop a better understanding of bacterial transmission during an outbreak.

Prevalence of Shiga toxin-producing Escherichia coli in ground beef and cattle feces from King County, Washington

Shiga toxin-producing Escherichia coli (STEC) is increasingly recognized as a common cause of diarrhea. STEC infection is a major public health threat because of its ability to cause serious and potentially life-threatening illnesses. The main reservoirs of STEC are believed to be the intestinal tracts of animals. Several studies have investigated the prevalence of STEC in various food items. The objective of this study was to determine the prevalence of STEC in the Seattle ground beef supply. In addition, the relative amount of STEC contamination between stores was compared, and possible differences between types of ground beef based on fat content (9, 16, and 23%) were investigated. A survey of Stx-I and/or Stx-II genes in fecal samples from cattle at a local slaughterhouse was also conducted. Of 296 ground beef samples tested from area retail grocery stores, 16.8% were positive for the presence of the toxin genes. Our data showed that there was no statistically significant difference (P > 0.05) in the prevalence of STEC between the ground beef samples of different fat contents and between grocery store chains. Of the 103 cattle fecal samples tested, 19 (18.4%) were found positive for the presence of Stx-I and/or Stx-II genes. The presence of a rather high percentage of STEC in the food supply in the absence of large number of cases suggests that not all STEC lineages are pathogenic for humans.

Identification of Escherichia coli O157:H7 and other enterohemorrhagic serotypes by EHEC- hlyA targeting, strand displacement amplification, and fluorescence polarization

Human disease caused by enterohemorrhagic E. coli O157:H7 and other serotypes (EHEC) has been associated with bovine fecal contamination of food and the environment. The range of serotypes, low infectious dose, and numerous transmission vehicles for EHEC render development of detection methods for this pathogen complex. In this study, the hemolysin gene (EHEC- hly A) was targeted with oligonucleotides, and probe-target hybrids were amplified using strand displacement amplification (SDA). Amplicons were resolved in the complete reaction mix through changes in the fluorescence polarization (FP) of a fluorescein-labeled detector probe hybridized to the amplicons during amplification. Results combining EHEC- hly A, SDA, and FP were obtained within 35 min of reaction initiation. The test specificity was determined on EHEC strains representing 13 serotypes (49 isolates); and control uropathogenic, commensal, and other organisms (10 isolates). Statistical analysis of results indicated a sensitivity in the reaction vessel to 4.3 bacteria (95% confidence interval), and a specificity for EHEC (n=59) at 100% (P=5.11E-17; i.e. P<<0.05). Detection based on combining EHEC- hly A, SDA, and FP was compatible with water sources directly associated with human infection (drinking and recreational supplies), and bovine drinking trough water representing an environmental matrix linked to the maintenance of an EHEC animal reservoir.

Economic impact of an Escherichia coli O157:H7 outbreak in Japan

We estimated the economic impact of an outbreak of foodborne diseases occurring from elementary school lunches in 1996 in which 268 persons in Iwate prefecture, Japan were infected with Escherichia coli O157:H7. This study assessed the impact of direct economic losses and indirect economic consequences due to this outbreak. The economic impact of the outbreak was estimated to be about 82,686,000 yen. The laboratory costs, about 21,204,000 yen, showed the highest ratio of the total cost of this outbreak (about 26%). Also, the cost of foodstuffs that were not purchased during the suspension of the lunch service (about 19%), personnel expenses paid to lunch service employees (about 17%), human illness costs (about 15%), and the repair costs of facilities (about 15%) showed up as a high ratio in the total cost, respectively. Because all patients were children, the productivity losses estimated were low as children were considered as dependants with no income. Instead, we estimated the lost income of the mothers of the children. The source of the contamination could not be identified. Therefore, no food industries suffered any setbacks where certain food items could not be used for daily consumption due to the outbreak.

Factors influencing the detection and enumeration of Escherichia coli O157:H7 on alfalfa seeds

Isolating Escherichia coli O157:H7 from batches of alfalfa seeds used to produce sprouts implicated in human illness has been difficult, perhaps due to nonhomogenous and very low-level contamination and inaccessibility of the pathogen entrapped in protected areas of the seed coat. We evaluated the effectiveness of various treatments in releasing E. coli O157:H7 from seeds. The influence of homogenization (blending or stomaching for 1 or 2 min), rinsing method (shaking for 5 min), soaking time (0. 1, 3, 6, or 15 h), soaking temperature (4 or 21 degrees C), and the addition of surfactants (0.1%, 0.5%, or 1.0% Tween 80 or Span 20) to rinse water was determined. Blending or stomaching for 1 or 2 min, and soaking for 1 h or longer at 4 or 21 degrees C, respectively, resulted in maximum release of E. coli O157:H7 from seeds. Soaking seeds at 37 degrees C for 15 h increased cell populations of E. coli O157:H7 by approximately 3.6 log10 CFU/g, likely due to bacterial growth. The maximum number of cells released from seeds by rinse water containing 1.0% Span 20 was at 21 degrees C, whereas at 37 degrees C, 0.1% or 0.5% Tween 80 was more effective. Detection of E. coli O157:H7 on seeds stored at 37 degrees C for up to 13 weeks and on sprouts derived from these seeds was compared. E. coli O157:H7 inoculated on seeds at 2.0 log10 CFU/g was detected after storage of seeds for up to 8 weeks at 37 degrees C and in sprouts produced from the seeds. The pathogen was not detected on seeds stored for 13 weeks at 37 degrees C and was not isolated from sprouts produced from these seeds. Identifying seed treatment methods that enhance removal of E. coli O157:H7 from alfalfa seeds can aid the isolation and enumeration of the pathogen on seeds. With a combination of optimal conditions for detecting the pathogen, i.e. soaking seeds for 1 h and pummeling seeds for 1 min, an enrichment step in modified tryptic soy broth (TSB), and the use of immunomagnetic beads for separation of E. coli O157:H7 cells, E. coli O157:H7 was detected in alfalfa seeds incubated at 37 degrees C for up to 8 weeks as effectively as in sprouts produced from the seeds.

Occurrence of parasites on fruits and vegetables in Norway

Between August 1999 and January 2001, samples of various fruits and vegetables obtained within Norway were analyzed by published methods for parasite contamination. Neither Cyclospora oocysts nor Ascaris (or other helminth) eggs were detected on any of the samples examined for these parasites. However, of the 475 samples examined for Cryptosporidium oocysts and Giardia cysts, 29 (6%) were found to be positive. No samples were positive for both parasites. Of the 19 Cryptosporidium-positive samples. 5 (26%) were in lettuce, and 14 (74%) in mung bean sprouts. Of the 10 Giardia-positive samples, 2 (20%) were in dill, 2 (20%) in lettuce, 3 (30%) in mung bean sprouts, 1 (10%) in radish sprouts, and 2 (20%) in strawberries. Mung bean sprouts were significantly more likely to be contaminated with Cryptosporidium oocysts or Giardia cysts than the other fruits and vegetables. Concentrations of Cryptosporidium and Giardia detected were generally low (mean of approximately 3 [oo]cysts per 100 g produce). Although some of the contaminated produce was imported (the majority, if sprouted seeds are excluded), there was no association between imported produce and detection of parasites. Crvptosporidium oocysts and Giardia cysts were also detected in water samples concerned with field irrigation and production of bean sprouts within Norway. This is the first time that parasites have been detected on vegetables and fruit obtained in a highly developed. wealthy country, without there being an outbreak situation. These findings may have important implications for global food safety.

Toxicity of Shiga toxin 1 in the central nervous system of rabbits

The action of Shiga toxin (Stx) on the central nervous system was examined in rabbits. Intravenous Stx1 was 44 times more lethal than Stx2 and acted more rapidly than Stx2. However, Stx1 accumulated more slowly in the cerebrospinal fluid than did Stx2. Magnetic resonance imaging demonstrated a predominance of Stx1-dependent lesions in the spinal cord. Pretreatment of the animals with anti-Stx1 antiserum intravenously completely protected against both development of brain lesions and mortality.