Phenotypic and genotypic characterization of enterotoxigenic Escherichia coli isolated from U.S. military personnel participating in Operation Bright Star, Egypt, from 2005 to 2009

Bacterial travellers' diarrhoea: A narrative review of literature published over the past 10 years

Travellers' diarrhoea (TD) is the most frequent illness experienced by international travellers to lower-income countries with bacterial agents considered to account for 80-90% of cases. In this review, we summarise evidence published on bacterial TD over the past 10 years, focusing on the epidemiology and aetiology of TD. Diarrhoeagenic Escherichia coli (DEC) continue to be the most commonly implicated bacteria in TD, although Enteropathogenic E. coli (EPEC) and Enteroaggregative E. coli (EAEC) now appear to be predominant where Enterotoxigenic E. coli (ETEC) was previously considered most prevalent globally. Where fluroquinolone resistance had primarily been documented for Campylobacter in Southeast Asia, widespread resistance has been observed in most regions of the world for multiple enteropathogens, including Shigella, Salmonella, ETEC and EAEC. Implementation of novel molecular methods for pathogen detection has led to identification of bacterial pathogens, including Clostridium difficile (with and without the use of prior antibiotics), Arcobacter species and Bacteroides fragilis, as aetiological agents in TD. The widespread resistance to first-line antibiotics in multiple bacterial enteropathogens warrants continued surveillance and re-evaluation of current treatment practices. Further investigations are required to determine the prevalence and geographical distribution of bacterial enteropathogens that have been more recently implicated in TD.

Clinical aspects of heat-labile and heat-stable toxin-producing enterotoxigenic Escherichia coli: A prospective study among Finnish travellers

BACKGROUND

Enterotoxigenic Escherichia coli (ETEC) is a major pathogen causing travellers' diarrhoea (TD) among visitors to low- and middle-income countries (LMIC). Scant data are available on rates of travel-acquired ETEC producing heat-labile (LT) and/or heat-stable (ST) toxin or its subtypes, STh (human) and STp (porcine) in various geographic regions, and on clinical pictures associated with each toxin.

METHODS

Using qPCR, we analysed LT, STh, and STp in stools positive for ETEC in a prospective study among 103 Finnish travellers visiting LMIC. They filled in questionnaires and provided stool samples before and after travel. We scrutinized geographic distribution of LT, STh, and STp ETEC findings, and association between these different ETEC subtypes and moderate/severe TD.

RESULTS

Among the 103 stool samples positive for ETEC toxins, the rate for LT was 76%, for STh 26%, and STp 41%. The rate for LT-only was 44%, for STh-only 6%, STp-only 16%, LT + STh 10%, LT + STp 15%, STh + STp 3%, and LT + STh + STp 8%. Findings varied by destination; the rates of LT, STh, and STp were 79%, 21%, and 57%, respectively, in Southern Asia (n = 14); 85%, 10%, and 20% in South-eastern Asia (n = 20); 84%, 13%, and 29% in Eastern Africa (n = 31); and 56%, 50%, and 63% in Western Africa (n = 32), respectively. Of travellers positive for LT, STh, and STp, 83%, 100%, and 88%, encountered TD; 35%, 55%, and 41% reported moderate/severe TD. STh was associated with moderate/severe TD.

CONCLUSIONS

Toxin findings varied by destination; multiple toxins were commonly detected. Moderate/severe TD was reported most frequently by subjects with STh-ETEC.

The Coli Surface Antigen CS3 of Enterotoxigenic Escherichia coli Is Differentially Regulated by H-NS, CRP, and CpxRA Global Regulators

Enterotoxigenic Escherichia coli produces a myriad of adhesive structures collectively named colonization factors (CFs). CS3 is a CF, which is assembled into fine wiry fibrillae encoded by the cstA-H gene cluster. In this work we evaluated the influence of environmental cues such as temperature, osmolarity, pH, and carbon source on the expression of CS3 genes. The transcription of cstH major pilin gene was stimulated by growth of the bacteria in colonization factor broth at 37°C; the presence of glycerol enhanced cstH transcription, while glucose at high concentration, high osmolarity, and the depletion of divalent cations such as calcium and magnesium repressed cstH expression. In addition, we studied the role of H-NS, CpxRA, and CRP global regulators in CS3 gene expression. H-NS and CpxRA acted as repressors and CRP as an activator of cstH expression. Under high osmolarity, H-NS, and CpxRA were required for cstH repression. CS3 was required for both, bacterial adherence to epithelial cells and biofilm formation. Our data strengthens the existence of a multi-factorial regulatory network that controls transcription of CS3 genes in which global regulators, under the influence of environmental signals, control the production of this important intestinal colonization factor.

Development of an enterotoxigenic Escherichia coli vaccine based on the heat-stable toxin

Infection with enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhea-related illness and death among children under 5 years of age in low– and middle-income countries (LMIC). Recent studies have found that it is the ETEC subtypes that produce the heat-stable enterotoxin (ST), irrespective of whether they also secrete the heat-labile enterotoxin (LT), which contribute most importantly to the disease burden in children from LMIC. Therefore, adding an ST toxoid would importantly complement ongoing ETEC vaccine development efforts. The ST’s potent toxicity, its structural similarity to the endogenous peptides guanylin and uroguanylin, and its poor immunogenicity have all complicated the advancement of ST-based vaccine development. Recent remarkable progress, however, including the unprecedented screening for optimal ST mutants, mapping of cross-reacting ST epitopes and improved ST-carrier coupling strategies (bioconjugation and genetic fusion), enables the rational design of safe, immunogenic, and well-defined ST-based vaccine candidates.

Resistant pathogens as causes of traveller's diarrhea globally and impact(s) on treatment failure and recommendations

BACKGROUND

: Diarrhea is a frequent clinical syndrome affecting international travellers. Bacterial etiologic agents have a long history of emergent antimicrobial resistance against commonly used antibiotics. Current approaches applying first-line antimicrobial therapy are being challenged by increasingly resistant organisms. This review summarizes recent epidemiological and clinical evidence of antibiotic resistance among enteropathogens causing traveller's diarrhea and the subsequent impact on current treatment recommendations.

METHODS

: The PubMed database was systemically searched for articles related to antibiotic susceptibility and diarrheal pathogens.

RESULTS

: Antibiotic resistance related to travellers' diarrhea has increased in recent years. Most notably, fluoroquinolone resistance has expanded from the Campylobacter -associated cases well documented in Southeast Asia in the 1990s to widespread occurrence, as well as increases among other common bacterial enteropathogens including, enterotoxigenic and enteroaggregative Escherichia coli , Shigella and non-typhoidal Salmonella . Multidrug resistance among enteropathogenic Enterobacteriacae and Campylobacter species create further challenges with the selection of empiric therapy. Treatment failures requiring early use of alternative agents, as well as delayed recovery comparable to placebo rates emphasize the impact of antimicrobial resistance on effective treatment.

CONCLUSIONS

: Although there are limitations in the available data, the increasing antibiotic resistance and adverse impact on clinical outcome require continued surveillance and reconsideration of practice guidelines.

Binding of CFA/I Pili of Enterotoxigenic Escherichia coli to Asialo-GM1 Is Mediated by the Minor Pilin CfaE

CFA/I pili are representatives of a large family of related pili that mediate the adherence of enterotoxigenic Escherichia coli to intestinal epithelial cells. They are assembled via the alternate chaperone-usher pathway and consist of two subunits, CfaB, which makes up the pilus shaft and a single pilus tip-associated subunit, CfaE. The current model of pilus-mediated adherence proposes that CFA/I has two distinct binding activities; the CfaE subunit is responsible for binding to receptors of unknown structure on erythrocyte and intestinal epithelial cell surfaces, while CfaB binds to various glycosphingolipids, including asialo-GM1. In this report, we present two independent lines of evidence that, contrary to the existing model, CfaB does not bind to asialo-GM1 independently of CfaE. Neither purified CfaB subunits nor CfaB assembled into pili bind to asialo-GM1. Instead, we demonstrate that binding activity toward asialo-GM1 resides in CfaE and this is essential for pilus binding to Caco-2 intestinal epithelial cells. We conclude that the binding activities of CFA/I pili for asialo-GM1, erythrocytes, and intestinal cells are inseparable, require the same amino acid residues in CfaE, and therefore depend on the same or very similar binding mechanisms.

Simple method for purification of enterotoxigenic Escherichia coli fimbriae

Enterotoxigenic Escherichia coli (ETEC) are endemic pathogens in the developing world. They frequently cause illness in travelers, and are among the most prevalent causes of diarrheal disease in children. Pathogenic ETEC strains employ fimbriae as adhesion factors to bind the luminal surface of the intestinal epithelium and establish infection. Accordingly, there is marked interest in immunoprophylactic strategies targeting fimbriae to protect against ETEC infections. Multiple strategies have been reported for purification of ETEC fimbriae, however none is ideal. Purification has typically involved the use of highly virulent wild-type strains. We report here a simple and improved method to purify ETEC fimbriae, which was applied to obtain two different Class 5 fimbriae types of clinical relevance (CFA/I and CS4) expressed recombinantly in E. coli production strains. Following removal from cells by shearing, fimbriae proteins were purified by orthogonal purification steps employing ultracentrifugation, precipitation, and ion-exchange membrane chromatography. Purified fimbriae demonstrated the anticipated size and morphology by electron microscopy analysis, contained negligible levels of residual host cell proteins, nucleic acid, and endotoxin, and were recognized by convalescent human anti-sera.

Molecular epidemiological view on Shiga toxin-producing Escherichia coli causing human disease in Germany: Diversity, prevalence, and outbreaks

Infections by intestinal pathogenic Escherichia coli (E. coli) are among those causing a high mortality and morbidity due to diarrheal disease and post infection sequelae worldwide. Since introduction of the Infection Protection Act in Germany 2001, these pathogens rank third among bacterial infections of the gastrointestinal tract. As a major pathovar Shiga toxin-producing E. coli (STEC) which include enterohemorrhagic E. coli (EHEC) play a leading role in occurrence of sporadic cases and disease outbreaks. An outstanding example is the large outbreak in spring 2011 caused by EHEC/EAEC O104:H4. To monitor and trace back STEC infections, national surveillance programs have been implemented including activities of the German National Reference Centre for Salmonella and other Enteric Bacterial Pathogens (NRC). This review highlights advances in our understanding of STEC in the last 20 years of STEC surveillance by the NRC. Here important characteristics of STEC strains from human infections and outbreaks in Germany between 1997 and 2013 are summarized.

Colonization factors of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a major cause of life-threatening diarrheal disease around the world. The major aspects of ETEC virulence are colonization of the small intestine and the secretion of enterotoxins which elicit diarrhea. Intestinal colonization is mediated, in part, by adhesins displayed on the bacterial cell surface. As colonization of the intestine is the critical first step in the establishment of an infection, it represents a potential point of intervention for the prevention of infections. Therefore, colonization factors (CFs) have been important subjects of research in the field of ETEC virulence. Research in this field has revealed that ETEC possesses a large array of serologically distinct CFs that differ in composition, structure, and function. Most ETEC CFs are pili (fimbriae) or related fibrous structures, while other adhesins are simple outer membrane proteins lacking any macromolecular structure. This chapter reviews the genetics, structure, function, and regulation of ETEC CFs and how such studies have contributed to our understanding of ETEC virulence and opened up potential opportunities for the development of preventive and therapeutic interventions.