Escherichia coli is the predominant nonpathogenic facultative flora of the human intestine. Some E. coli strains, however, have developed the ability to cause disease of the gastrointestinal, urinary, or central nervous system in even the most robust human hosts. Diarrheagenic strains of E. coli can be divided into at least six different categories with corresponding distinct pathogenic schemes. Taken together, these organisms probably represent the most common cause of pediatric diarrhea worldwide. Several distinct clinical syndromes accompany infection with diarrheagenic E. coli categories, including traveler’s diarrhea (enterotoxigenic E. coli), hemorrhagic colitis and hemolytic-uremic syndrome (enterohemorrhagic E. coli), persistent diarrhea (enteroaggregative E. coli), and watery diarrhea of infants (enteropathogenic E. coli). This review discusses the current level of understanding of the pathogenesis of the diarrheagenic E. coli strains and describes how their pathogenic schemes underlie the clinical manifestations, diagnostic approach, and epidemiologic investigation of these important pathogens.

Diarrheagenic Escherichia coli

Few microorganisms are as versatile as Escherichia coli. An important member of the normal intestinal microflora of humans and other mammals, E. coli has also been widely exploited as a cloning host in recombinant DNA technology. But E. coli is more than just a laboratory workhorse or harmless intestinal inhabitant; it can also be a highly versatile, and frequently deadly, pathogen. Several different E. coli strains cause diverse intestinal and extraintestinal diseases by means of virulence factors that affect a wide range of cellular processes.

Pathogenic Escherichia coli

http://envismadrasuniv.org/Physiology/pdf/Gut%20flora%20in%20health%20and%20disease.pdf

Gut flora in health and disease

Infectious Diseases Society of America.

Bacteria belonging to the genus Klebsiella frequently cause human nosocomial infections. In particular, the medically most important Klebsiella species, Klebsiella pneumoniae, accounts for a significant proportion of hospital-acquired urinary tract infections, pneumonia, septicemias, and soft tissue infections. The principal pathogenic reservoirs for transmission of Klebsiella are the gastrointestinal tract and the hands of hospital personnel. Because of their ability to spread rapidly in the hospital environment, these bacteria tend to cause nosocomial outbreaks. Hospital outbreaks of multidrug-resistant Klebsiella spp., especially those in neonatal wards, are often caused by new types of strains, the so-called extended-spectrum-β-lactamase (ESBL) producers. The incidence of ESBL-producing strains among clinical Klebsiella isolates has been steadily increasing over the past years. The resulting limitations on the therapeutic options demand new measures for the management of Klebsiella hospital infections. While the different typing methods are useful epidemiological tools for infection control, recent findings about Klebsiella virulence factors have provided new insights into the pathogenic strategies of these bacteria. Klebsiella pathogenicity factors such as capsules or lipopolysaccharides are presently considered to be promising candidates for vaccination efforts that may serve as immunological infection control measures.

/pdf/klebsiella-spp-as-nosocomial-pathogens-epidemiology-taxonomy-1qbzenizx4.pdf

Klebsiella spp. as Nosocomial Pathogens: Epidemiology, Taxonomy, Typing Methods, and Pathogenicity Factors

The evidence that H. pylori causes gastritis in humans comes from both primary and secondary observations. The most important primary observations are the human volunteer studies, the animal models, and the treatment studies with antimicrobial agents. Supporting information comes from studies showing the specific association of H. pylori infection with type B gastritis and with gastric (but not intestinal) epithelial cells; the specific ultrastructural lesions, including adherence pedestals; the ubiquity and stability of the immune response; the response to bismuth treatment; and the association with epidemic gastritis and hypochlorhydria. It is important to note that all of Koch's postulates have been fulfilled, and despite nearly universal initial skepticism, no evidence exists against the hypothesis that H. pylori plays an etiologic role in type B gastritis. Therefore, it is reasonable to conclude that H. pylori is a pathogen in humans. The known features of H. pylori infection are listed in. Infection is chronic and common throughout the world, with a higher prevalence in developing countries than in developed countries. The prevalence of H. pylori infection increases with age in parallel with that of gastritis. Acquisition of H. pylori infection does not appear to have any seasonality, and infection is equally common among men and women. Without a significant animal or environmental reservoir for human strains of H. pylori, person-to-person contact appears to be the most likely mode of transmission. Exactly how the organism is transmitted from the stomach of one person to that of another remains unclear. Also unknown are the factors which determine who becomes ill after infection; why one person has gastritis alone while another person develops a duodenal ulcer; and how the traditional risk factors for ulcer disease, such as smoking, aspirin, and alcohol, interact with H. pylori infection. Finally, the long term neoplastic consequences of infection must be understood. Further elucidation of the natural history of H. pylori and the consequences of H. pylori infection is the most important goal for future study.

The Epidemiology of Helicobacter pylori Infection

Epidemiology of campylobacter jejuni infections

Transcutaneous immunization, a topical vaccine application, combines the advantages of needle-free delivery while targeting the immunologically rich milieu of the skin. In animal studies, this simple technique induces robust systemic and mucosal antibodies against vaccine antigens. Here, we demonstrate safe application of a patch containing heat-labile enterotoxin (LT, derived from Escherichia coli) to humans, resulting in robust LT-antibody responses. These findings indicate that TCI is feasible for human immunization, and suggest that TCI may enhance efficacy as well as improve vaccine delivery.

David N. Taylor

Papers

The Epidemiology of Helicobacter pylori Infection

Epidemiology of campylobacter jejuni infections

Transcutaneous immunization: a human vaccine delivery strategy using a patch.

A placebo-controlled trial of Lactobacillus GG to prevent diarrhea in undernourished Peruvian children☆☆☆★

Safety and immunogenicity of a recombinant M2e-flagellin influenza vaccine (STF2.4xM2e) in healthy adults.