Abstract
Purpose of review The aim of this review is to highlight recent advances in knowledge of bacterial enteric infections. We focus on understanding of enterohemorrhagic Escherichia coli O157:H7 and Campylobacter jejuni infections, and to link these acute events with long-term consequences in a susceptible host, including irritable bowel syndrome and chronic inflammatory bowel diseases.
Recent findings Enterohemorrhagic E. coli and C. jejuni are zoonotic infections that are acquired from exposure to tainted food (undercooked hamburger and chicken, respectively) and contaminated drinking water. Noninvasive E. coli O157:H7 elaborates Shiga-like toxins and protein effectors that are injected, via a molecular syringe that is encoded by a bacterial type 3 secretion system, into infected eukaryotic cells. Less is known about the precise virulence properties of enteroinvasive Campylobacter strains, but both enteric pathogens are able to disrupt polarized epithelial monolayers resulting in increased uptake of macromolecules and antigens.
Summary An improved understanding of the epidemiology, pathobiology and mechanisms underlying infectious enterocolitides will provide the basis for developing new intervention strategies including, for example, the use of probiotics, to interrupt the infectious process.
Introduction
The past year has brought major advances in our understanding of the gut microbiota in settings of both health[1,2] and disease.[3••,4] Technological advances in molecular genetics and bioinformatics have yielded novel insights regarding the intestinal microbiome. For example, even short courses of oral antibiotics provided to healthy adult volunteers impact on the composition of the colonic microflora for several months after the cessation of therapy[5,6] that can predispose them to an intercurrent bacterial infection.[7] Similarly, acute enteric infections alter composition of the normal resident commensal microbiota.[8] This disruption in the composition of the gut microbiome, termed dysbiosis, may be improved by the ingestion of probiotics,[9] which are defined as exogenous live organisms that – when taken in sufficient amounts – have a beneficial effect on the host. Increasing evidence also points to long-term chronic consequences of acute infectious insults, including the development of postinfectious irritable bowel syndrome (IBS)[10] and chronic inflammatory bowel diseases (IBD).[11,12]
Emerging Pathogens
It has been stated that there are roughly 1400 recognized species of human pathogens.[13] More than half of these are zoonotic infections arising from contamination by exposure to birds, bats, and ruminants. Of these, some 177 organisms are considered as emerging or reemerging human pathogens. It is clear, however, that this is likely to underestimate the number and range of pathogens that can infect people. Potential pitfalls in the identification of enteric pathogens include the timing of collecting fecal samples (that is, the infection can clear even though symptoms persist), the use of antimicrobial agents or other compounds that inhibit the growth of an organism, the choice of culture medium and the atmospheric condition of the culture. In addition, it is simply not possible to successfully culture the range of organisms known to colonize mucosal surfaces. The use of molecular technologies, that are increasingly accessible to the diagnostic microbiology laboratory, serves to identify novel microbes that are not able to be cultured using currently available laboratory culture facilities and methodologies.[14,15]
Rather than providing a general overview, this review will focus on two Gram-negative enteric bacterial pathogens with vast human morbidity worldwide:[16•] enterohemorrhagic Escherichia coli O157:H7 and Campylobacter jejuni.
Purpose of review The aim of this review is to highlight recent advances in knowledge of bacterial enteric infections. We focus on understanding of enterohemorrhagic Escherichia coli O157:H7 and Campylobacter jejuni infections, and to link these acute events with long-term consequences in a susceptible host, including irritable bowel syndrome and chronic inflammatory bowel diseases.
Recent findings Enterohemorrhagic E. coli and C. jejuni are zoonotic infections that are acquired from exposure to tainted food (undercooked hamburger and chicken, respectively) and contaminated drinking water. Noninvasive E. coli O157:H7 elaborates Shiga-like toxins and protein effectors that are injected, via a molecular syringe that is encoded by a bacterial type 3 secretion system, into infected eukaryotic cells. Less is known about the precise virulence properties of enteroinvasive Campylobacter strains, but both enteric pathogens are able to disrupt polarized epithelial monolayers resulting in increased uptake of macromolecules and antigens.
Summary An improved understanding of the epidemiology, pathobiology and mechanisms underlying infectious enterocolitides will provide the basis for developing new intervention strategies including, for example, the use of probiotics, to interrupt the infectious process.
Introduction
The past year has brought major advances in our understanding of the gut microbiota in settings of both health[1,2] and disease.[3••,4] Technological advances in molecular genetics and bioinformatics have yielded novel insights regarding the intestinal microbiome. For example, even short courses of oral antibiotics provided to healthy adult volunteers impact on the composition of the colonic microflora for several months after the cessation of therapy[5,6] that can predispose them to an intercurrent bacterial infection.[7] Similarly, acute enteric infections alter composition of the normal resident commensal microbiota.[8] This disruption in the composition of the gut microbiome, termed dysbiosis, may be improved by the ingestion of probiotics,[9] which are defined as exogenous live organisms that – when taken in sufficient amounts – have a beneficial effect on the host. Increasing evidence also points to long-term chronic consequences of acute infectious insults, including the development of postinfectious irritable bowel syndrome (IBS)[10] and chronic inflammatory bowel diseases (IBD).[11,12]
Emerging Pathogens
It has been stated that there are roughly 1400 recognized species of human pathogens.[13] More than half of these are zoonotic infections arising from contamination by exposure to birds, bats, and ruminants. Of these, some 177 organisms are considered as emerging or reemerging human pathogens. It is clear, however, that this is likely to underestimate the number and range of pathogens that can infect people. Potential pitfalls in the identification of enteric pathogens include the timing of collecting fecal samples (that is, the infection can clear even though symptoms persist), the use of antimicrobial agents or other compounds that inhibit the growth of an organism, the choice of culture medium and the atmospheric condition of the culture. In addition, it is simply not possible to successfully culture the range of organisms known to colonize mucosal surfaces. The use of molecular technologies, that are increasingly accessible to the diagnostic microbiology laboratory, serves to identify novel microbes that are not able to be cultured using currently available laboratory culture facilities and methodologies.[14,15]
Rather than providing a general overview, this review will focus on two Gram-negative enteric bacterial pathogens with vast human morbidity worldwide:[16•] enterohemorrhagic Escherichia coli O157:H7 and Campylobacter jejuni.