Evaluation of BBL CHROMagar O157 versus sorbitol-MacConkey medium for routine detection of Escherichia coli O157 in a centralized regional clinical microbiology laboratory

Mentha longifolia Essential Oil and Pulegone in Edible Coatings of Alginate and Chitosan: Effects on Pathogenic Bacteria in Lactic Cheese

Mentha longifolia is a valuable medicinal and aromatic plant that belongs to Lamiaceae family. This study looked at the antibacterial effects of M. longifolia essential oil and pulegone in edible coatings made of chitosan and alginate on the growth of Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli in cheese. For this purpose, first fresh mint plant was collected from the cold region of Jiroft in Kerman province. Plant samples were dried in the shade at ambient temperature, and essential oil was prepared using Clevenger. The essential oil was analyzed by gas chromatography using mass spectrometric (GC/MS) detection. The major composition of M. longifolia oil was pulegone (26.07%), piperitone oxide (19.72%), and piperitone (11.88%). The results showed that adding M. longifolia essential oils and pulegone to edible coatings significantly reduced the growth of bacteria during storage. The bacterial population decreased by increasing the concentration of chitosan, M. longifolia, and pulegone in edible coatings. When the effects of pulegone and M. longifolia essential oils on bacteria were compared, it was found that pulegone had a stronger effect on bacterial population reduction. Coating treatments showed more antibacterial activity on E. coli than other bacteria. In general, the results of this research showed that alginate and chitosan coatings along with M. longifolia essential oil and its active ingredient pulegone had antibacterial effects against S. aureus, L. monocytogenes, and E. coli in cheese.

Genome-Enabled Molecular Subtyping and Serotyping for Shiga Toxin-Producing Escherichia coli

Foodborne pathogens are a major public health burden in the United States, leading to 9.4 million illnesses annually. Since 1996, a national laboratory-based surveillance program, PulseNet, has used molecular subtyping and serotyping methods with the aim to reduce the burden of foodborne illness through early detection of emerging outbreaks. PulseNet affiliated laboratories have used pulsed-field gel electrophoresis (PFGE) and immunoassays to subtype and serotype bacterial isolates. Widespread use of serotyping and PFGE for foodborne illness surveillance over the years has resulted in the accumulation of a wealth of routine surveillance and outbreak epidemiological data. This valuable source of data has been used to understand seasonal frequency, geographic distribution, demographic information, exposure information, disease severity, and source of foodborne isolates. In 2019, PulseNet adopted whole genome sequencing (WGS) at a national scale to replace PFGE with higher-resolution methods such as the core genome multilocus sequence typing. Consequently, PulseNet's recent shift to genome-based subtyping methods has rendered the vast collection of historic surveillance data associated with serogroups and PFGE patterns potentially unusable. The goal of this study was to develop a bioinformatics method to associate the WGS data that are currently used by PulseNet for bacterial pathogen subtyping to previously characterized serogroup and PFGE patterns. Previous efforts to associate WGS to PFGE patterns relied on predicting DNA molecular weight based on restriction site analysis. However, these approaches failed owing to the non-uniform usage of genomic restriction sites by PFGE restriction enzymes. We developed a machine learning approach to classify isolates to their most probable serogroup and PFGE pattern, based on comparisons of genomic k-mer signatures. We applied our WGS classification method to 5,970 Shiga toxin-producing Escherichia coli (STEC) isolates collected as part of PulseNet's routine foodborne surveillance activities between 2003 and 2018. Our machine learning classifier is able to associate STEC WGS to higher-level serogroups with very high accuracy and lower-level PFGE patterns with somewhat lower accuracy. Taken together, these classifications support the ability of public health investigators to associate currently generated WGS data with historical epidemiological knowledge linked to serogroups and PFGE patterns in support of outbreak surveillance for food safety and public health.

Epidemiology and genetic screening of diarrheagenic Escherichia coli among symptomatic and asymptomatic children

PURPOSE

Enteropathogens are frequently associated with diarrheal disease. Knowledge of their etiology and epidemiology is essential for the prevention and control of the sickness. This study describes the microbiological and epidemiological features of diarrheal disease in 197 symptomatic and 223 asymptomatic under-five-year-old children from southeastern Brazil, between January 2015 and September 2016.

METHODS

Isolation of Escherichia coli, Salmonella, Shigella and Campylobacter was realized by culture. E. coli strains were screened by multiplex PCR, PFGE and O:H serotyping. Antimicrobial susceptibility testing was also performed.

RESULTS

Most of the 127 enteropathogens isolated were diarrheagenic E. coli (96.1 %), with predominance of several serotypes of enteropathogenic E. coli (EPEC) and enteroaggregative E. coli (EAEC). Age, sex, rotavirus vaccination, recent use of antibiotics and previous contact with pets, were factors that revealed no significant effects on the probability of infection by the predominant pathogens. Even so, higher incomes could be related to a lesser chance of testing positive for EPEC. Evidence of possible EAEC clonal spread was detected, as well as genetic similarity among strains from both symptomatic and asymptomatic children. Resistance to antimicrobial agents was more pronounced among EAEC than EPEC.

CONCLUSION

The occurrence of genetically similar diarrheagenic E. coli in both groups of children, likewise resistant to these agents, underscores the importance of establishing strategies for the prevention of outbreaks, especially among low-income households.

Multiplex Nucleic Acid Amplification Testing to Diagnose Gut Infections: Challenges, Opportunities, and Result Interpretation

Multiplex nucleic acid testing is increasingly used to diagnose childhood gastroenteritis. The advantages of this disruptive technology include rapidity, sensitivity, and ability to detect pathogenic viruses, bacteria, and parasites simultaneously. The drawbacks are its capacity to identify organisms of uncertain clinical significance in North American children, cost, and inability to provide viable bacteria for strain typing by public health authorities. However, this technology will certainly improve our knowledge of the causes of human gut infections. As data emerge, physicians should interpret results cautiously, and, most important, consider the context of the presentation before making clinical decisions based on the readouts.

Detection, Characterization, and Typing of Shiga Toxin-Producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) are responsible for gastrointestinal diseases reported in numerous outbreaks around the world. Given the public health importance of STEC, effective detection, characterization and typing is critical to any medical laboratory system. While non-O157 serotypes account for the majority of STEC infections, frontline microbiology laboratories may only screen for STEC using O157-specific agar-based methods. As a result, non-O157 STEC infections are significantly under-reported. This review discusses recent advances on the detection, characterization and typing of STEC with emphasis on work performed at the Alberta Provincial Laboratory for Public Health (ProvLab). Candidates for the detection of all STEC serotypes include chromogenic agars, enzyme immunoassays (EIA) and quantitative real time polymerase chain reaction (qPCR). Culture methods allow further characterization of isolates, whereas qPCR provides the greatest sensitivity and specificity, followed by EIA. The virulence gene profiles using PCR arrays and stx gene subtypes can subsequently be determined. Different non-O157 serotypes exhibit markedly different virulence gene profiles and a greater prevalence of stx1 than stx2 subtypes compared to O157:H7 isolates. Finally, recent innovations in whole genome sequencing (WGS) have allowed it to emerge as a candidate for the characterization and typing of STEC in diagnostic surveillance isolates. Methods of whole genome analysis such as single nucleotide polymorphisms and k-mer analysis are concordant with epidemiological data and standard typing methods, such as pulsed-field gel electrophoresis and multiple-locus variable number tandem repeat analysis while offering additional strain differentiation. Together these findings highlight improved strategies for STEC detection using currently available systems and the development of novel approaches for future surveillance.

Assessment of commercial chromogenic solid media for the detection of non-O157 Shiga toxin-producing Escherichia coli (STEC)

Detection of Shiga toxin-producing Escherichia coli (STEC) has evolved significantly since the introduction of sorbitol-MacConkey agar. This study compares four chromogenic media (CHROMagar™ STEC, Rainbow® O157 agar, CHROMagar™ O157, and Colorex® O157) in their identification of non-O157 STEC. When 161 non-O157 STEC were directly inoculated onto each medium, detection rates on CHROMagar™ STEC, Rainbow® O157 agar, CHROMagar™ O157 and Colorex® O157 were 90%, 70%, 3.7% and 6.8%, respectively. Tellurite minimal inhibitory concentrations (MICs) correlated with growth on CHROMagar™ STEC as 20 of 22 isolates with poor or no growth had MICs ≤1μg/mL. Stool spiking experiments revealed that CHROMagar™ STEC had the highest recovery of the six most common non-O157 STEC, ranging from 30% (in mucoid stool) to 98% (in watery stool). When using clinical stool samples, CHROMagar™ STEC had a sensitivity, specificity, positive predictive value, and negative predictive value of 84.6%, 87%, 13.9%, and 99.6%, respectively.

Practical Guidance for Clinical Microbiology Laboratories: Diagnosis of Bacterial Gastroenteritis

Bacterial gastroenteritis is a disease that is pervasive in both the developing and developed worlds. While for the most part bacterial gastroenteritis is self-limiting, identification of an etiological agent by bacterial stool culture is required for the management of patients with severe or prolonged diarrhea, symptoms consistent with invasive disease, or a history that may predict a complicated course of disease. Importantly, characterization of bacterial enteropathogens from stool cultures in clinical laboratories is one of the primary means by which public health officials identify and track outbreaks of bacterial gastroenteritis. This article provides guidance for clinical microbiology laboratories that perform stool cultures. The general characteristics, epidemiology, and clinical manifestations of key bacterial enteropathogens are summarized. Information regarding optimal specimen collection, transport, and processing and current diagnostic tests and testing algorithms is provided. This article is an update of Cumitech 12A (P. H. Gilligan, J. M. Janda, M. A. Karmali, and J. M. Miller, Cumitech 12A, Laboratory diagnosis of bacterial diarrhea, 1992).

Shiga Toxin Producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) is among the common causes of foodborne gastroenteritis. STEC is defined by the production of specific toxins, but within this pathotype there is a diverse group of organisms. This diversity has important consequences for understanding the pathogenesis of the organism, as well as for selecting the optimum strategy for diagnostic testing in the clinical laboratory. This review includes discussions of the mechanisms of pathogenesis, the range of manifestations of infection, and the several different methods of laboratory detection of Shiga toxin-producing E coli.

Light scattering sensor for direct identification of colonies of Escherichia coli serogroups O26, O45, O103, O111, O121, O145 and O157

Background

Shiga-toxin producing Escherichia coli (STEC) have emerged as important foodborne pathogens, among which seven serogroups (O26, O45, O103, O111, O121, O145, O157) are most frequently implicated in human infection. The aim was to determine if a light scattering sensor can be used to rapidly identify the colonies of STEC serogroups on selective agar plates.

Methodology/Principal Findings

Initially, a total of 37 STEC strains representing seven serovars were grown on four different selective agar media, including sorbitol MacConkey (SMAC), Rainbow Agar O157, BBL CHROMagarO157, and R&F E. coli O157:H7, as well as nonselective Brain Heart Infusion agar. The colonies were scanned by an automated light scattering sensor, known as BARDOT (BActerial Rapid Detection using Optical scattering Technology), to acquire scatter patterns of STEC serogroups, and the scatter patterns were analyzed using an image classifier. Among all of the selective media tested, both SMAC and Rainbow provided the best differentiation results allowing multi-class classification of all serovars with an average accuracy of more than 90% after 10–12 h of growth, even though the colony appearance was indistinguishable at that early stage of growth. SMAC was chosen for exhaustive scatter image library development, and 36 additional strains of O157:H7 and 11 non-O157 serovars were examined, with each serogroup producing unique differential scatter patterns. Colony scatter images were also tested with samples derived from pure and mixed cultures, as well as experimentally inoculated food samples. BARDOT accurately detected O157 and O26 serovars from a mixed culture and also from inoculated lettuce and ground beef (10-h broth enrichment +12-h on-plate incubation) in the presence of natural background microbiota in less than 24 h.

Conclusions

BARDOT could potentially be used as a screening tool during isolation of the most important STEC serovars on selective agar plates from food samples in less than 24 h.

Shiga toxin-producing Escherichia coli: a single-center, 11-year pediatric experience

The aim of this study was to identify the best practices for the detection of Shiga toxin-producing Escherichia coli (STEC) in children with diarrheal illness treated at a tertiary care center, i.e., sorbitol-MacConkey (SMAC) agar culture, enzyme immunoassay (EIA) for Shiga toxin, or the simultaneous use of both methods. STEC was detected in 100 of 14,997 stool specimens submitted for enteric culture (0.7%), with 65 cases of E. coli O157. Among E. coli O157 isolates, 57 (88%) were identified by both SMAC agar culture and EIA, 6 (9%) by SMAC agar culture alone, and 2 (3%) by EIA alone. Of the 62 individuals with diarrheal hemolytic uremic syndrome (HUS) seen at our institution during the study period, 16 (26%) had STEC isolated from cultures at our institution and 15 (24%) had STEC isolated at other institutions. No STEC was recovered in 31 cases (50%). Of the HUS cases in which STEC was isolated, 28 (90%) were attributable to E. coli O157 and 3 (10%) were attributable to non-O157 STEC. Consistent with previous studies, we have determined that a subset of E. coli O157 infections will not be detected if an agar-based method is excluded from the enteric culture workup; this has both clinical and public health implications. The best practice would be concomitant use of an agar-based method and a Shiga toxin EIA, but a Shiga toxin EIA should not be considered to be an adequate stand-alone test for detection of E. coli O157 in clinical samples.

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

Multistate outbreak of Escherichia coli O145 infections associated with romaine lettuce consumption, 2010

Non-O157 Shiga toxin-producing Escherichia coli (STEC) can cause severe illness, including hemolytic uremic syndrome (HUS). STEC O145 is the sixth most commonly reported non-O157 STEC in the United States, although outbreaks have been infrequent. In April and May 2010, we investigated a multistate outbreak of STEC O145 infection. Confirmed cases were STEC O145 infections with isolate pulsed-field gel electrophoresis patterns indistinguishable from those of the outbreak strain. Probable cases were STEC O145 infections or HUS in persons who were epidemiologically linked. Case-control studies were conducted in Michigan and Ohio; food exposures were analyzed at the restaurant, menu, and ingredient level. Environmental inspections were conducted in implicated food establishments, and food samples were collected and tested. To characterize clinical findings associated with infections, we conducted a chart review for case patients who sought medical care. We identified 27 confirmed and 4 probable cases from five states. Of these, 14 (45%) were hospitalized, 3 (10%) developed HUS, and none died. Among two case-control studies conducted, illness was significantly associated with consumption of shredded romaine lettuce in Michigan (odds ratio [OR] = undefined; 95% confidence interval [CI] = 1.6 to undefined) and Ohio (OR = 10.9; 95% CI = 3.1 to 40.5). Samples from an unopened bag of shredded romaine lettuce yielded the predominant outbreak strain. Of 15 case patients included in the chart review, 14 (93%) had diarrhea and abdominal cramps and 11 (73%) developed bloody diarrhea. This report documents the first foodborne outbreak of STEC O145 infections in the United States. Current surveillance efforts focus primarily on E. coli O157 infections; however, non-O157 STEC can cause similar disease and outbreaks, and efforts should be made to identify both O157 and non-O157 STEC infections. Providers should test all patients with bloody diarrhea for both non-O157 and O157 STEC.

Evaluation of CHROMagar STEC and STEC O104 chromogenic agar media for detection of Shiga Toxin-producing Escherichia coli in stool specimens

The performance of CHROMagar STEC and CHROMagar STEC O104 (CHROMagar Microbiology, Paris, France) media for the detection of Shiga toxin-producing Escherichia coli (STEC) was assessed with 329 stool specimens collected over 14 months from patients with suspected STEC infections (June 2011 to August 2012). The CHROMagar STEC medium, after an enrichment broth step, allowed the recovery of the STEC strain from 32 of the 39 (82.1%) Shiga toxin-positive stool specimens, whereas the standard procedure involving Drigalski agar allowed the recovery of only three additional STEC strains. The isolates that grew on CHROMagar STEC medium belonged to 15 serotypes, including the prevalent non-sorbitol-fermenting (NSF) O157:H7, O26:H11, and O104:H4 serotypes. The sensitivity, specificity, and positive and negative predictive values for the CHROMagar STEC medium were between 89.1% and 91.4%, 83.7% and 86.7%, 40% and 51.3%, and 98% and 98.8%, respectively, depending on whether or not stx-negative eae-positive E. coli was considered atypical enteropathogenic E. coli (EPEC) or STEC that had lost Shiga toxin genes during infection. In conclusion, the good performance of CHROMagar STEC agar medium, in particular, the high negative predictive value, and its capacity to identify NSF O157:H7 as well as common non-O157 STEC may be useful for clinical bacteriology, public health, and reference laboratories; it could be used in addition to a method targeting Shiga toxins (detection of stx genes by PCR, immunodetection of Shiga toxins in stool specimens, or Vero cell cytotoxicity assay) as an alternative to O157 culture medium. This combined approach should allow rapid visualization of both putative O157 and non-O157 STEC colonies for subsequent characterization, essential for real-time surveillance of STEC infections and investigations of outbreaks.

Usability and performance of CHROMagar STEC medium in detection of Shiga toxin-producing Escherichia coli strains

The performance and usability of CHROMagar STEC medium (CHROMagar Microbiology, Paris, France) for routine detection of Shiga toxin-producing Escherichia coli (STEC) strains were examined. The ability of the medium to selectively propagate STEC strains differing by their serotypes and virulence genes was studied with a collection of diarrheagenic E. coli isolates (n = 365) consisting of 49 different serotypes and with non-STEC and other bacterial isolates (n = 264). A total of 272 diarrheagenic E. coli (75.0%) isolates covering 24 different serotypes grew on CHROMagar STEC. The highest detection sensitivities were observed within the STEC serogroups O26 (90.0%), O111 (100.0%), O121 (100.0%), O145 (100.0%), and O157 (84.9%), and growth on CHROMagar STEC was highly associated with the presence of the tellurite resistance gene (terD). The specificity of the medium was 98.9%. In addition, CHROMagar STEC was used in parallel with a Shiga toxin-detecting immunoassay (Ridaquick Verotoxin/O157 Combi; R-biopharm, Darmstadt, Germany) to screen fecal specimens (n = 47) collected from patients suffering from hemorrhagic diarrhea. Positive growth on CHROMagar STEC was confirmed by the Premier EHEC enzyme immunoassay (Meridian Bioscience, Inc., Cincinnati, OH), and discrepant results between the two screening methods were confirmed by stx gene-detecting PCR. All 16 of the 47 stool samples that showed positive growth on CHROMagar STEC were also positive in the confirmatory tests. CHROMagar STEC proved to be an interesting option for STEC screening, allowing good detection sensitivity and specificity and permitting strain isolation for further outbreak investigations when required.

Mouldy feed, mycotoxins and Shiga toxin - producing Escherichia coli colonization associated with Jejunal Hemorrhage Syndrome in beef cattle

Background

Both O157 and non-O157 Shiga toxin - producing Escherichia coli (STECs) cause serious human disease outbreaks through the consumption of contaminated foods. Cattle are considered the main reservoir but it is unclear how STECs affect mature animals. Neonatal calves are the susceptible age class for STEC infections causing severe enteritis. In an earlier study, we determined that mycotoxins and STECs were part of the disease complex for dairy cattle with Jejunal Hemorrhage Syndrome (JHS). For STECs to play a role in the development of JHS, we hypothesized that STEC colonization should also be evident in beef cattle with JHS. Aggressive medical and surgical therapies are effective for JHS, but rely on early recognition of clinical signs for optimal outcomes suggesting that novel approaches must be developed for managing this disease. The main objective of this study was to confirm that mouldy feeds, mycotoxins and STEC colonization were associated with the development of JHS in beef cattle.

Results

Beef cattle developed JHS after consuming feed containing several types of mycotoxigenic fungi including Fusarium poae, F. verticillioides, F. sporotrichioides, Penicillium roqueforti and Aspergillus fumigatus. Mixtures of STECs colonized the mucosa in the hemorrhaged tissues of the cattle and no other pathogen was identified. The STECs expressed Stx1 and Stx2, but more significantly, Stxs were also present in the blood collected from the lumen of the hemorrhaged jejunum. Feed extracts containing mycotoxins were toxic to enterocytes and 0.1% of a prebiotic, Celmanax Trademark, removed the cytotoxicity in vitro. The inclusion of a prebiotic in the care program for symptomatic beef calves was associated with 69% recovery.

Conclusions

The current study confirmed that STECs and mycotoxins are part of the disease complex for JHS in beef cattle. Mycotoxigenic fungi are only relevant in that they produce the mycotoxins deposited in the feed. A prebiotic, Celmanax Trademark, acted as a mycotoxin binder in vitro and interfered with the progression of disease.

A prebiotic, Celmanax™, decreases Escherichia coli O157:H7 colonization of bovine cells and feed-associated cytotoxicity in vitro

Background

Escherichia coli O157:H7 is the most common serovar of enterohemorrhagic E. coli associated with serious human disease outbreaks. Cattle are the main reservoir with E. coli O157:H7 inducing hemorrhagic enteritis in persistent shedding beef cattle, however little is known about how this pathogen affects cattle health. Jejunal Hemorrhage Syndrome (JHS) has unclear etiology but the pathology is similar to that described for E. coli O157:H7 challenged beef cattle suggestive that E. coli O157:H7 could be involved. There are no effective treatments for JHS however new approaches to managing pathogen issues in livestock using prebiotics and probiotics are gaining support. The first objective of the current study was to characterize pathogen colonization in hemorrhaged jejunum of dairy cattle during natural JHS outbreaks. The second objective was to confirm the association of mycotoxigenic fungi in feeds with the development of JHS and also to identify the presence of potential mycotoxins. The third objective was to determine the impact of a prebiotic, Celmanax™, or probiotic, Dairyman's Choice™ paste, on the cytotoxicity associated with feed extracts in vitro. The fourth objective was to determine the impact of a prebiotic or a probiotic on E. coli O157:H7 colonization of mucosal explants and a bovine colonic cell line in vitro. The final objective was to determine if prebiotic and probiotic feed additives could modify the symptoms that preceded JHS losses and the development of new JHS cases.

Findings

Dairy cattle developed JHS after consuming feed containing several types of mycotoxigenic fungi including Fusarium culmorum, F. poae, F. verticillioides, F. sporotrichioides, Aspergillusflavus, Penicillium roqueforti, P. crustosum, P. paneum and P. citrinum. Mixtures of Shiga toxin - producing Escherichia coli (STEC) colonized the mucosa in the hemorrhaged tissues of the cattle and no other pathogen was identified. The STECs expressed Stx1 and Stx2, but more significantly, Stxs were also present in the blood clot blocking the jejunum. Mycotoxin analysis of the corn crop confirmed the presence of fumonisin, NIV, ZEAR, DON, 15-ADON, 3-ADON, NEO, DAS, HT-2 and T-2. Feed extracts were toxic to enterocytes and 0.1% Celmanax™ removed the cytotoxicity in vitro. There was no effect of Dairyman's Choice™ paste on feed-extract activity in vitro. Fumonisin, T-2, ZEAR and DON were toxic to bovine cells and 0.1% Celmanax™ removed the cytotoxicity in vitro. Celmanax™ also directly decreased E. coli O157:H7 colonization of mucosal explants and a colonic cell line in a dose-dependent manner. There was no effect of Dairyman's Choice™ paste on E. coli O157:H7 colonization in vitro. The inclusion of the prebiotic and probiotic in the feed was associated with a decline in disease.

Conclusion

The current study confirmed an association between mycotoxigenic fungi in the feed and the development of JHS in cattle. This association was further expanded to include mycotoxins in the feed and mixtures of STECs colonizing the severely hemorrhaged tissues. Future studies should examine the extent of involvement of the different STEC in the infection process. The prebiotic, Celmanax™, acted as an anti-adhesive for STEC colonization and a mycotoxin binder in vitro. Future studies should determine the extent of involvement of the prebiotic in altering disease.

Development of PCR assays for detection of Escherichia coli O157:H7 in meat products

A multiplex polymerase chain reaction (PCR) procedure based on fliC(h7) and rfbE genes was developed for the detection of Escherichia coli O157:H7 in raw pork meat and ready-to-eat (RTE) meat products. Two different DNA extraction procedures were evaluated for application on meat products. MasterPure™ DNA Purification kit in combination with immunomagnetic separation was found to be the best method in a meat system. The optimized PCR included an enrichment step in brilliant green bile 2% broth at 37 °C. This method was applied to artificially inoculated meat and RTE meat products with different concentrations of E. coli O157:H7. The results indicate that the PCR assay developed could sensitively and specifically detect E. coli O157:H7 in raw pork meat and RTE meat products in approximately 10h, including a 6h enrichment step. Thus, this method could be proposed for screening E. coli O157:H7 in raw pork and RTE meat products.

Comparison of Shiga toxin-producing Escherichia coli detection methods using clinical stool samples

Molecular diagnostic tools capable of identifying Shiga toxin-specific genetic determinants in stool specimens permit an unbiased approach to detect Shiga toxin-producing Escherichia coli (STEC) in clinical samples and can indicate when culture-based isolation methods are required. It is increasingly recognized that clinically relevant STEC are not limited to the singular O157 serotypes, and therefore diagnostic assays targeting toxin-encoding determinants must be able to account for any genetic variation that exists between serotypes. In this study conventional PCR and four real-time PCR assays (HybProbe, TaqMan, SYBR Green, and LUX) targeting the stx1 and stx2 Shiga toxin coding sequences were used to identify STEC in enriched stool samples (n = 36) and a panel of O157 and non-O157 strains (n = 64). PCR assays targeting stx1 and stx2 had variable specificity and sensitivity values with enriched stool samples. Molecular assays using DNA from pure cultures revealed that some primers were not sensitive to all stx2 variants. This evaluation concluded that the TaqMan-based probes were most appropriate in high throughput clinical diagnostic laboratories in consideration of cost, turn around time, and assay performance.

Isolation and detection of Shiga toxin-producing Escherichia coli in clinical stool samples using conventional and molecular methods

The isolation of Shiga toxin-producing Escherichia coli (STEC) other than serogroup O157 from clinical stool samples is problematic due to the lack of differential phenotypic characteristics from non-pathogenic E. coli. The development of molecular reagents capable of identifying both toxin and serogroup-specific genetic determinants holds promise for a more comprehensive characterization of stool samples and isolation of STEC strains. In this study, 876 stool samples from paediatric patients with gastroenteritis were screened for STEC using a cytotoxicity assay, commercial immunoassay and a conventional PCR targeting Shiga-toxin determinants. In addition, routine culture methods for isolating O157 STEC were also performed. The screening assays identified 45 stools presumptively containing STEC, and using non-differential culture techniques a total of 20 O157 and 22 non-O157 strains were isolated. These included STEC serotypes O157 : H7, O26 : H11, O121 : H19, O26 : NM, O103 : H2, O111 : NM, O115 : H18, O121 : NM, O145 : NM, O177 : NM and O5 : NM. Notably, multiple STEC serotypes were isolated from two clinical stool samples (yielding O157 : H7 and O26 : H11, or O157 : H7 and O103 : H2 isolates). These data were compared to molecular serogroup profiles determined directly from the stool enrichment cultures using a LUX real-time PCR assay targeting the O157 fimbrial gene lpfA, a microsphere suspension array targeting allelic variants of espZ and a gnd-based molecular O-antigen serogrouping method. The genetic profile of individual stool cultures indicated that the espZ microsphere array and lpfA real-time PCR assay could accurately predict the presence and provide preliminary typing for the STEC strains present in clinical samples. The gnd-based molecular serogrouping method provided additional corroborative evidence of serogroup identities. This toolbox of molecular methods provided robust detection capabilities for STEC in clinical stool samples, including co-infection of multiple serogroups.