Status of vaccine research and development for enterotoxigenic Escherichia coli

Evaluation of the Probiotic Strain Bifidobacterium longum subsp. Infantis CECT 7210 Capacities to Improve Health Status and Fight Digestive Pathogens in a Piglet Model

Probiotics have been demonstrated to be useful to enhance gut health and prevent gastrointestinal infections. The objective of this study is to demonstrate the potential of the probiotic strain Bifidobacterium longum subsp. infantis CECT 7210 (B. infantis IM1) to prevent and fight intestinal disease by using a Salmonella Typhimurium (Trial 1) or an enterotoxigenic Escherichia coli K88 (Trial 2) oral challenge in a weaning piglet model. Seventy-two piglets were used in each trial. After an adaptation period, animals were orally challenged. One animal per pen was euthanized at Days 4 and 8/9 (Trial 1/Trial 2) post-inoculation (PI). Animal performance, clinical signs, pathogen excretion, fermentation, immune response, and intestinal morphology were evaluated. In Trial 1, most parameters responded to the challenge, whereas, in Trial 2, effects were much milder. Consistent effects of the probiotic were detected in both experiments: Reduction of pathogen excretion (P = 0.043 on Day 3 PI, Trial 1) or ileal colonization (33% reduction of animals with countable coliforms; P = 0.077, Trial 2); increases in intraepithelial lymphocytes (P = 0.002 on Day 8 PI in Trial 1, P = 0.091 on Day 4 PI in Trial 2), and improvement of the fermentation profile by increasing butyric acid in non-challenged animals [P challenge × probiotic (interaction) = 0.092 in Trial 1 and P = 0.056 in Trial 2] concomitant with an enhancement of the villus:crypt ratio on Day 8/9 PI (P interaction = 0.091 for Trial 1 and P = 0.006 for Trial 2). Challenged animals treated with the probiotic showed reduced feed intakes (P interaction = 0.019 in Trial 1 and P = 0.020 in Trial 2) and had lower short-chain fatty acid concentrations in the colon (P interaction = 0.008 in Trial 1 and P = 0.082 in Trial 2). In conclusion, this probiotic demonstrated potential to reduce the intestinal colonization by pathogens and to stimulate local immune response. However, effects on feed intake, microbial fermentation, and intestinal architecture showed a differential pattern between challenged and non-challenged animals. Effects of the probiotic intervention were dependent on the structure of the ecosystem in which it was applied.

Defining cases of severe pediatric diarrhea for an efficacy trial of an enterotoxigenic Escherichia coli (ETEC) vaccine: Report on an international workshop, Washington DC, March 2016

Enterotoxigenic Escherichia coli (ETEC) causes severe acute watery diarrhea. No ETEC vaccine is available but candidates are in development, including ETVAX, an oral, whole-cell inactivated vaccine. ETVAX is being tested in a descending-age trial in Bangladesh. If found safe and immunogenic, investigators may test it for efficacy in children. Like oral rotavirus vaccines, we expect that ETVAX will be most effective at decreasing the incidence of moderate-to-severe ETEC episodes. Thus, for an efficacy trial outcome, it will be necessary to triage patients into moderate-to-severe versus mild disease. A severity scale specific to ETEC does not exist. To develop this scale, PATH convened a committee of international experts for a two-day meeting to strategize on diagnostic scale development. The workshop began with four presentations. The first described existing scales, item selection, and issues related to validation, reliability, and ease of use. The other three presentations provided details on the following published scores: the DHAKA score, validated for use with Bangladeshi children seeking diarrhea treatment; a modified-Vesikari score for evaluating North American outpatient children with diarrhea; and the Community Diarrhea Assessment (CODA) score developed for passive-case surveillance of Peruvian children with diarrhea. Following the presentations and discussion, the committee made several recommendations including: modifying existing scores to make them ETEC-centric; evaluating scoring systems against an objective measure of dehydration (i.e., the percent change in a child's bodyweight following rehydration); and adding an item to the scale measuring ETEC effects on growth faltering. The committee also discussed using available data sets to evaluate scores, but was concerned that if investigators characterized patients using different procedures than prescribed by the score, the results would be difficult to interpret. Committee members suggested new data collection and recommended conducting studies in Sub-Saharan Africa. The study results would be presented for peer-review and to regulatory authorities.

Antibodies Damage the Resilience of Fimbriae, Causing Them To Be Stiff and Tangled

As adhesion fimbriae are a major virulence factor for many pathogenic Gram-negative bacteria, they are also potential targets for antibodies. Fimbriae are commonly required for initiating the colonization that leads to disease, and their success as adhesion organelles lies in their ability to both initiate and sustain bacterial attachment to epithelial cells. The ability of fimbriae to unwind and rewind their helical filaments presumably reduces their detachment from tissue surfaces with the shear forces that accompany significant fluid flow. Therefore, the disruption of functional fimbriae by inhibiting this resilience should have high potential for use as a vaccine to prevent disease. In this study, we show that two characteristic biomechanical features of fimbrial resilience, namely, the extension force and the extension length, are significantly altered by the binding of antibodies to fimbriae. The fimbriae that were studied are normally expressed on enterotoxigenic Escherichia coli, which are a major cause of diarrheal disease. This alteration in biomechanical properties was observed with bivalent polyclonal antifimbrial antibodies that recognize major pilin subunits but not with the Fab fragments of these antibodies. Thus, we propose that the mechanism by which bound antibodies disrupt the uncoiling of natural fimbria under force is by clamping together layers of the helical filament, thereby increasing their stiffness and reducing their resilience during fluid flow. In addition, we propose that antibodies tangle fimbriae via bivalent binding, i.e., by binding to two individual fimbriae and linking them together. Use of antibodies to disrupt physical properties of fimbriae may be generally applicable to the large number of Gram-negative bacteria that rely on these surface-adhesion molecules as an essential virulence factor.

IMPORTANCE

Our study shows that the resiliency of colonization factor antigen I (CFA/I) and coli surface antigen 2 (CS2) fimbriae, which are current targets for vaccine development, can be compromised significantly in the presence of antifimbrial antibodies. It is unclear how the humoral immune system specifically interrupts infection after the attachment of enterotoxigenic Escherichia coli (ETEC) to the epithelial surface. Our study indicates that immunoglobulins, in addition to their well-documented role in adaptive immunity, can mechanically damage the resilience of fimbriae of surface-attached ETEC, thereby revealing a new mode of action. Our data suggest a mechanism whereby antibodies coat adherent and free-floating bacteria to impede fimbrial resilience. Further elucidation of this possible mechanism is likely to inform the development and refinement of preventive vaccines against ETEC diarrhea.

Colonization Factors in Enterotoxigenic Escherichia coli Strains in Travelers to Mexico, Guatemala, and India Compared with Children in Houston, Texas

Enterotoxigenic Escherichia coli (ETEC) can be attributed to around 200 million diarrheal episodes and 380,000 deaths in the developing regions. Travelers' diarrhea occurs in 15-40% of travelers to developing regions with ETEC being the most important etiologic agent. This study aims to describe the distribution of enterotoxins and colonization factor (CF) profiles of ETEC isolates from stool samples of adult travelers acquiring diarrhea in Mexico, Guatemala, and India and a group of children with acute diarrhea in Houston, TX, between 2007 and 2012. The heat-labile/heat-stable (LT/ST) enterotoxins and CFs from 252 patients were determined using polymerase chain reaction assay. Among the 252 ETEC isolates, 15% were LT-only, 58% were ST-only, and 28% produced both LT and ST. The distribution of LT-only (12-15%) and ST-only (55-56%) isolates was similar between Latin American and Indian sites. The most prevalent CF was CS21, expressed in 65% of the isolates followed by CS6 (25%) and CS3 (17%). Among the international travelers, 64% of the ETEC isolates expressed CS21. CS21 was expressed in 46% of isolates from Latin America compared with 96% of isolates from India (P < 0.0001). CS21 was expressed in 85% isolates from Houston children. CS21 was increasingly found in ST-only (P = 0.003) and ST/LT (P = 0.026) ETEC compared with LT-only ETEC. High frequency of finding CS21 among recent isolates of ETEC over a wide geographic distribution warrants additional studies on this CF. Highly conserved CS21 is an important target for potential multivalent ETEC vaccines.

Individual-specific changes in the human gut microbiota after challenge with enterotoxigenic Escherichia coli and subsequent ciprofloxacin treatment

Background

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrhea in inhabitants from low-income countries and in visitors to these countries. The impact of the human intestinal microbiota on the initiation and progression of ETEC diarrhea is not yet well understood.

Results

We used 16S rRNA (ribosomal RNA) gene sequencing to study changes in the fecal microbiota of 12 volunteers during a human challenge study with ETEC (H10407) and subsequent treatment with ciprofloxacin.

Five subjects developed severe diarrhea and seven experienced few or no symptoms. Diarrheal symptoms were associated with high concentrations of fecal E. coli as measured by quantitative culture, quantitative PCR, and normalized number of 16S rRNA gene sequences. Large changes in other members of the microbiota varied greatly from individual to individual, whether or not diarrhea occurred. Nonetheless the variation within an individual was small compared to variation between individuals. Ciprofloxacin treatment reorganized microbiota populations; however, the original structure was largely restored at one and three month follow-up visits.

Conclusion

Symptomatic ETEC infections, but not asymptomatic infections, were associated with high fecal concentrations of E. coli. Both infection and ciprofloxacin treatment caused variable changes in other bacteria that generally reverted to baseline levels after three months.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2777-0) contains supplementary material, which is available to authorized users.