Evaluation of colony-based examinations of diarrheagenic Escherichia coli in stool specimens: low probability of detection because of low concentrations, particularly during the early stage of gastroenteritis

Increased sensitivity of enterotoxigenic Escherichia coli detection in stool samples using oligonucleotide immobilized-magnetic nanoparticles

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A rapid detection of ETEC DNA with high sensitivity and specificity.

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The combination between magnetic nanoparticles and molecular technique.

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100-folds increase of sensitivity compared with gold standard.

PCR detection of enterotoxigenic Escherichia-coli (ETEC) can be used directly on stool sample. However, it still has limitations due to presence of PCR inhibitors and interferences. This study, oligonucleotide primer specific to ETEC was immobilized onto MNPs and applied for separation and enrichment of ETEC-DNA from contaminants in stool after boiling. DNA separation efficiency was evaluated using conventional PCR and magneto-PCR-enzyme linked-gene-assay (MELGA). Due to high specificity of primer and efficiency of nanoparticles to bring down PCR inhibitors, DNA separation using primer-immobilized-MNPs exhibited 100-fold increase of sensitivity compared to that using simple boiling. Moreover, the sensitivities in stool were increased from 10⁸ to 10⁶ CFU/mL and 10⁴ to 10² CFU/mL when PCR products were detected by gel electrophoresis and MELGA, respectively. Results suggested that oligonucleotide-immobilized-MNPs combined with boiling DNA extraction method was successfully used to separate the DNA of ETEC in stool with high sensitivity using MELGA.

Rapid and Accurate Diagnosis Based on Real-Time PCR Cycle Threshold Value for the Identification of Campylobacter jejuni, astA Gene-Positive Escherichia coli, and eae Gene-Positive E. coli

We previously developed a multiplex real-time PCR assay (Rapid Foodborne Bacterial Screening 24 ver.5, [RFBS24 ver.5]) for simultaneous detection of 24 foodborne bacterial targets. Here, to overcome the discrepancy of the results from RFBS24 ver.5 and bacterial culture methods (BC), we analyzed 246 human clinical samples from 49 gastroenteritis outbreaks using RFBS24 ver.5 and evaluated the correlation between the cycle threshold (CT) value of RFBS24 ver.5 and the BC results. The results showed that the RFBS24 ver.5 was more sensitive than BC for Campylobacter jejuni and Escherichia coli harboring astA or eae, with positive predictive values (PPV) of 45.5-87.0% and a kappa coefficient (KC) of 0.60-0.92, respectively. The CTs were significantly different between BC-positive and -negative samples (p ＜ 0.01). All RFBS24 ver.5-positive samples were BC-positive under the lower confidence interval (CI) limit of 95% or 99% for the CT of the BC-negative samples. We set the 95% or 99% CI lower limit to the determination CT (d-CT) to discriminate for assured BC-positive results (d-CTs: 27.42-30.86), and subsequently the PPVs (94.7%-100.0%) and KCs (0.89-0.95) of the 3 targets were increased. Together, we concluded that the implication of a d-CT-based approach would be a valuable tool for rapid and accurate diagnoses using the RFBS24 ver.5 system.

High Prevalence of Diarrheagenic Escherichia coli among Children with Diarrhea in Kenya

Diarrheagenic Escherichia coli (DEC) is an important agent of endemic and epidemic diarrhea worldwide, particularly in developing countries. DEC cannot be differentiated from commensal E. coli on selective media, although there are a few exceptions. Most studies use the colony isolation method, which cannot detect low numbers of DEC, and therefore, these studies might underestimate the incidence of DEC. In the present study, we employed a colony sweep method with real-time PCR targeting virulence genes of 5 categories of DEC; this technique can detect very low numbers of DEC among hundreds of commensal E. coli. DEC was detected in 171 (55.9%) of 306 children with diarrhea in Kenya. The prevalence of DEC in Kenya was notably higher than that (30 in 143, 21.0%) in Indonesia. Occurrences of multiple DEC infection in Kenya were frequent (69 in 306, 23.2%), suggesting that the source of DEC infection may be related to grossly contaminated food and water. In contrast, only 9 (6.0%) of 150 healthy adults in Kenya carried DEC. Considering that healthy adults naturally harbor non-DEC, it is interesting how children exclude DEC but not non-DEC as they grow up. Several mechanisms, such as mucosal immunity and intestinal microbiota, might be involved in the exclusion of DEC.

Detection of diarrhoeagenic Escherichia coli in clinical and environmental water sources in South Africa using single-step 11-gene m-PCR

Escherichia coli (E. coli) consists of commensal (ComEC) and diarrhoeagenic (DEC) groups. ComEC are detected using traditional culture methods. Conformational steps are performed after culturing if it is required to test for the presence of DEC, increasing cost and time in obtaining the results. The aim of this study was to develop a single-step multiplex polymerase chain reaction (m-PCR) that can simultaneously amplify genes associated with DEC and ComEC, with the inclusion of controls to monitor inhibition. A total of 701 samples, taken from clinical and environmental water sources in South Africa, were analysed with the optimised m-PCR which targeted the eaeA, stx1, stx2, lt, st, ial, eagg, astA and bfp virulence genes. The mdh and gapdh genes were included as an internal and external control, respectively. The presence of the external control gapdh gene in all samples excluded any possible PCR inhibition. The internal control mdh gene was detected in 100 % of the environmental and 85 % of the clinical isolates, confirming the classification of isolates as E. coli PCR positive samples. All DEC types were detected in varying degrees from the mdh positive environmental and clinical isolates. Important gene code combinations were detected for clinical isolates of 0.4 % lt and eagg. However, 2.3 % of eaeA and ial, and 8.7 % of eaeA and eagg were reported for environmental water samples. The E. coli astA toxin was detected as positive at 35 and 17 % in environmental isolates and clinical isolates, respectively. Interestingly, 25 % of the E. coli astA toxin detected in environmental isolates and 17 % in clinical isolates did not contain any of the other virulence genes tested. In conclusion, the optimised single-step 11-gene m-PCR reactions could be successfully used for the identification of pathogenic and non-pathogenic E. coli types. The m-PCR was also successful in showing monitoring for PCR inhibition to ensure correct reporting of the results.

A DNA pooling based system to detect Escherichia coli virulence factors in fecal and wastewater samples

The availability of a useful tool for simple and timely detection of the most important virulent varieties of Escherichia coli is indispensable. To this end, bacterial DNA pools which had previously been categorized were obtained from isolated colonies as well as selected in terms of utilized phenotype; the pools were assessed by two PCR Multiplex for the detection of virulent E. coli eaeA, bfpA, stx1, stx2, ipaH, ST, LT, and aatA genes, with the 16S gene used as DNA control. The system was validated with 66 fecal samples and 44 wastewater samples. At least one positive isolate was detected by a virulent gene among the 20 that were screened. The analysis of fecal samples from children younger than 6 years of age detected frequencies of 25% LT positive strains, 8.3% eae, 8.3% bfpA, 16.7% ipaH, as well as 12.5 % aatA and ST. On the other hand, wastewater samples revealed frequencies of 25.7% eaeA positive, 30.3% stx1, 15.1% LT and 19.7% aatA. This study is an initial step toward carrying out epidemiological field research that will reveal the presence of these bacterial varieties.

Survey of culture, goldengate assay, universal biosensor assay, and 16S rRNA Gene sequencing as alternative methods of bacterial pathogen detection

Cultivation-based assays combined with PCR or enzyme-linked immunosorbent assay (ELISA)-based methods for finding virulence factors are standard methods for detecting bacterial pathogens in stools; however, with emerging molecular technologies, new methods have become available. The aim of this study was to compare four distinct detection technologies for the identification of pathogens in stools from children under 5 years of age in The Gambia, Mali, Kenya, and Bangladesh. The children were identified, using currently accepted clinical protocols, as either controls or cases with moderate to severe diarrhea. A total of 3,610 stool samples were tested by established clinical culture techniques: 3,179 DNA samples by the Universal Biosensor assay (Ibis Biosciences, Inc.), 1,466 DNA samples by the GoldenGate assay (Illumina), and 1,006 DNA samples by sequencing of 16S rRNA genes. Each method detected different proportions of samples testing positive for each of seven enteric pathogens, enteroaggregative Escherichia coli (EAEC), enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), Shigella spp., Campylobacter jejuni, Salmonella enterica, and Aeromonas spp. The comparisons among detection methods included the frequency of positive stool samples and kappa values for making pairwise comparisons. Overall, the standard culture methods detected Shigella spp., EPEC, ETEC, and EAEC in smaller proportions of the samples than either of the methods based on detection of the virulence genes from DNA in whole stools. The GoldenGate method revealed the greatest agreement with the other methods. The agreement among methods was higher in cases than in controls. The new molecular technologies have a high potential for highly sensitive identification of bacterial diarrheal pathogens.

[Etiological bacterial level in enterohemorrhagic Escherichia coli infection feces and chromogenic culture medium CHROMagar STEC usefulness]

We report a case of enterohemorrhagic Escherichia coli (EHEC) infection in which EHEC was not detected by culture on DHL agar medium. The proportion of EHEC bacterial count to enterobacterial count in feces was 1.7%, and the detection probability by 5-colony angling was low (8.1%). The probability of angling detection using CHROMagar STEC, a chromogenic medium for detecting EHEC, was high (100%). An additional and collection test was done using E. coli bacterial solutions to which two main sera groups--O157 and O26 were added. The maximum detectable level in the bacterial solution with O157 was 10(3)-10(4) CFU/mL in DHL and 10(2) CFU/mL in CHROMagar STEC. Bacterial solution levels with O26 were 10(3) CFU/mL in DHL and 10(2) CFU/mL in CHROMagar STEC. Assuming that the EHEC bacterial amount in feces of those with EHEC infection is low, we speculated that CHROMagar STEC may be useful as on EHEC screening medium.

Systematic review: the epidemiology and clinical features of travellers' diarrhoea

BACKGROUND

Travellers' diarrhoea is the most common medical complaint among persons venturing into developing areas from industrialized regions.

AIM

To review recent developments dealing with microbiological, clinical, pathophysiological and therapeutic aspects of travellers' diarrhoea.

METHODS

The author's extensive file plus a review of publications listed in PubMed on January 22, 2009 on the topic of travellers' diarrhoea were reviewed.

RESULTS

Travellers' diarrhoea is largely caused by detectable and undetected bacterial enteropathogens, explaining the remarkable effectiveness of antibacterial agents in prophylaxis and therapy of the illness. A number of host genetic polymorphisms have been recently linked with susceptibility to travellers' diarrhoea. Novel antisecretory agents are being developed for treatment considering their physiological effects in acute diarrhoea. All travellers should be armed with one of three antibacterial drugs, ciprofloxacin, rifaximin or azithromycin, before their trips to use in self therapy should diarrhoea occur during travel. Loperamide may treat milder forms of travellers' diarrhoea and can be employed with antibacterial drugs.

CONCLUSIONS

Diarrhoea will continue to plague international travellers to high-risk regions. More studies of the incidence rate, relative important of the various pathogens by geographical region of the world, host risk factors and optimal therapeutic approach are needed.

Diagnosis and treatment of acute or persistent diarrhea

Studies of microbial pathogens and the toxins they produce are important for determining the mechanisms by which they cause disease and spread throughout a population. Some bacteria produce secretory enterotoxins (such as cholera toxin or the heat-labile or stable enterotoxins produced by Escherichia coli) that invade cells directly. Others invade cells or produce cytotoxins (such as those produced by Shigella, enteroinvasive E coli, or Clostridium difficile) that damage cells or trigger host responses that cause small or large bowel diseases (such as enteroaggregative or enteropathogenic E coli or Salmonella). Viruses (such as noroviruses and rotaviruses) and protozoa (such as Cryptosporidium, Giardia, or Entamoeba histolytica) disrupt cell functions and cause short- or long-term disease. Much epidemiologic data about these pathogens have been collected from community- and hospital-acquired settings, as well as from patients with traveler's or persistent diarrhea. These studies have led to practical approaches for prevention, diagnosis, and treatment.

Expert review of the evidence base for prevention of travelers' diarrhea

The most frequent illness among persons traveling from developed to developing countries is travelers' diarrhea. Travelers to high-risk regions traditionally have been educated to exercise care in food and beverage selection. Innovative research is needed to identify ways to motivate people to exercise this care and to determine its value. Chemoprophylaxis can be recommended for certain groups while monitoring for safety, drug resistance, and efficacy against all forms of bacterial diarrhea. Research to evaluate the value of immunoprophylaxis is recommended. In the following document, the authors used an evidence base when available to determine strength and quality of evidence and when data were lacking, the panel experts provided consensus opinion.

Enterotoxigenic Escherichia coli and diffusely adherent E. coli as likely causes of a proportion of pathogen-negative travelers' diarrhea--a PCR-based study

BACKGROUND

Enteropathogens cannot be identified in 40% to 50% of subjects with travelers' diarrhea (TD).

METHODS

We used polymerase chain reaction (PCR) methods to look for the presence of two bacterial causes of diarrhea in a large group of international travelers after failing to detect a pathogen by conventional tests. DNA was isolated from the diarrheal stool and subjected to PCR from 162 subjects from whom we earlier failed to identify a pathogen in a previous study and included 54 from Antigua, Guatemala, 39 from Guadalajara, Mexico, 29 from Kolkata, India, and 40 from Goa, India. Gene products for enterotoxigenic Escherichia coli (ETEC)--LT (heat-labile enterotoxin) and ST (heat-stable enterotoxin)--and diffusely adherent E. coli (DAEC), afa/dr (Afa fimbrial and Dr nonfimbrial family of adhesins), were used.

RESULTS

At least one gene product was identified in diarrhea stool samples of 47 of 162 (29%) subjects. ETEC virulence genes (LT, ST) were found in 34 (21%) samples studied, with rates of occurrence ranging from 8% in Goa to 39% for the samples from Guatemala (p = 0.0006). A large number of ST-only strains explained the high ETEC rate in Guatemala. DAEC afa/dr family of adhesions was identified in between 8 and 14% of the samples.

CONCLUSIONS

ETEC and DAEC were implicated in nearly one-third of the subjects initially diagnosed as pathogen negative. Direct PCR results from stools are consistent with the previous assumption that most undiagnosed TD is bacterial in nature and also highlights the potential value that PCR can add to studies designed to evaluate treatment and preventive interventions for TD, including vaccines.

Impact of diversity of colonizing strains on strategies for sampling Escherichia coli from fecal specimens

Of 49 subjects, 21 were colonized with more than one strain of Escherichia coli and 12 subjects had at least one strain present in fewer than 20% of colonies. The ability to accurately characterize E. coli strain diversity is directly related to the number of colonies sampled and the underlying prevalence of the strain.

Rapid culture-independent quantitative detection of enterotoxigenic Escherichia coli in surface waters by real-time PCR with molecular beacon

Rapid and reliable detection of enterotoxigenic Escherichia coli (ETEC) is critical for the management of the waterborne diseases threatening human lives worldwide. In this study, a culture-independent real-time PCR assay, in molecular beacon format was designed and validated for detection and quantitative enumeration of ETEC harboring LT1 gene (encoding heat labile toxin) in surface waters contaminated by fecal pollutants of human and animal origin. It was observed that the assay was able to detect 2 CFU/mL of ETEC (r = 0.997; PCR efficiency = 99.8%) from water samples spiked by a reference organism (E. coli MTCC 723). In the presence of 10(6) CFU/mL of nonpathogenic E. coli(E. coli DH5alpha), the lowest detection limit from spiked water samples was 4 CFU/mL. The assay was 500 times more sensitive than conventional PCR using the same oligomers (Student's t test p < 0.05). The assay could specifically detect and quantify ETEC (1.2 x 10(3) to 1.4 x 10(6) CFU/100 mL) in polluted surface waters of river Gomti. The rapid culture-independent assay developed in this study for detection and quantitative enumeration of ETEC can be used for preliminary monitoring of surface waters to prevent waterborne outbreaks.