Escherichia coli diarrhoea

Single Dose Treatments in Tropical Infectious Diarrhoea

Single dose treatments have the important advantages of simple administration, excellent compliance, short-lived side effects (if any) and short period of drug pressure. However, drugs used for single dose treatments must possess important characteristics, namely, long half-life, effective concentration in tissues over a long period, and low toxicity. In tropical medicine, such drugs are an important advance in the treatment of malaria (mefloquine and halofantrine), schistosomiasis (praziquantel and metrifonate), filariasis (ivermectin), and genitourinary tract and intestinal infections.

Intestinal infections are one of the most frequent problems in tropical medicine. While a large number of cases of diarrhoea are of viral (rotavirus) or bacterial (Salmonella, Escherichia coli) origin, necessitating only oral rehydration, some are of parasitological origin (Giardia, Entamoeba histolytica, Strongyloides, Trichuris, Schistosoma) and can be cured by a single dose treatment (tinidazole, secnidazole, ivermectin, albendazole, praziquantel). Secnidazole is the nitroimidazole with the longest half-life and is, therefore, used in single dose treatments for Giardia, acute intestinal amoebiasis and E. histolytica cyst carriers. Single dose treatments of most intestinal parasites will be a major advance in the management of tropical infectious diarrhoea. In the next decade, opportunistic intestinal infections (Cryptosporidium, Isospora, Enterocytozoon) in AIDS patients that are refractory to treatment could be the major problem.

Flow cytometric analysis for adhesion of Vibrio cholerae to human intestinal epithelial cell

The adhesion of Vibrio cholerae O1 strains to human intestinal epithelial cell, Intestine 407, was analyzed by flow cytometer. According to positive percentages of Intestine 407 cells adhered by V. cholerae, two groups of V. cholerae strains were classified as follows: more adhesive (more than 50%), less adhesive (less than 50%) strains. In addition, the fluorescence intensity after attachment of V. cholerae was directly correlated to the number of the microorganisms. It was concluded that flow cytometry is a useful and objective method for analyzing adhesion of V. cholerae to cultured cells.

Characterization of a novel hemagglutinin of diarrhea-associated Escherichia coli that has characteristics of diffusely adhering E. coli and enteroaggregative E. coli

Escherichia coli 73-1 (serotype O73:H33) and 5-2 (serotype O89:H-) isolated from patients with diarrhea adhered to tissue culture cells (HeLa and HEp-2) as well as coverslips (plastic and glass) in a diffuse pattern. Adherence of strain 73-1 was mediated by a 110-kbp plasmid designated pEDA1 and correlated with D-mannose-resistant hemagglutinin (MRHA) detected with bovine, sheep, or human erythrocytes. The MRHA region was duplicated on pEDA1 and mediated the production of the 57-kDa outer membrane protein whose N-terminal amino acid sequence was hydrophobic. In accordance with MRHA and adherence, the 57-kDa outer membrane protein was observed best at 37 degrees C and to a lesser extent at 25 degrees C. In human intestine, adherence to mucus and colonic epithelium was obvious. No detectable pili were observed. The enteroaggregative E. coli heat-stable enterotoxin 1 (EAST1) gene, whose nucleotide sequence was 99.1% homologous to that of enteroaggregative E. coli, was present adjacent to the MRHA region on pEDA1. Strain 5-2 also exhibited MRHA activities and adherence and had sequences corresponding to those of the MRHA region and EAST1 gene. The data suggest that strain 73-1 (and strain 5-2), which has characteristics of both diffusely adhering E. coli and enteroaggregative E. coli, possesses a novel hemagglutinin associated with diffuse adherence.

Actin accumulation associated with clustered and localized adherence in Escherichia coli isolated from patients with diarrhea

Escherichia coli D2 (serotype 07:H-) that was isolated from a child with diarrhea hybridized with an F1845 DNA probe used to detect diffuse adherence. Strain D2 adhered to tissue culture cells (HeLa and HEp-2 cells) in a clustered pattern but did not autoagglutinate on the cell surface and induced the elongation of microvilli after 3 h of incubation. After 6 h of incubation, the infected cells were positive for fluorescent-actin staining at the site of clustered adherence. When analyzed with a confocal laser scanning microscope, each D2 cell was surrounded by accumulated actin in a capsule-like formation. Capsule-like, accumulated actin was also observed with enteropathogenic E. coli (EPEC), although in this case, actin accumulation was associated with EPEC microcolonies in a localized pattern. Four other strains of F1845 DNA probe-positive, diffusely adhering E. coli were negative for actin accumulation. Strain D2 did not hybridize with EPEC attaching and effacing DNA or EPEC adherence factor DNA probes. In addition, clustered D2 cells were found inside tissue culture cells. The data suggest a novel infectious mechanism as well as genetic heterogeneity of F1845 DNA probe-positive E. coli. Capsule-like, accumulated actin may protect the bacteria from host defense mechanisms.

Bacterial diarrhoea

Diarrhoeal disease caused by enteric bacterial pathogens has become less prevalent in industrialized countries, but remains an important cause of morbidity and mortality in developing countries. Although better management of acute diarrhoeal episodes has led to more favourable outcomes, persistent diarrhoea remains a problem for which risk factors are being recognized and associated bacterial pathogens identified. Unusual or intractable diarrhoea should alert health workers to the possibility of impaired immune function, which is associated with a range of enteric pathogens and opportunistic infections. Improved microbiological methods have resulted in more frequent detection of pathogens in association with diarrhoea, as well as greater understanding of pathogenesis. Clinical features of diarrhoeal disease and mechanisms involved in pathogenesis are discussed in relation to specific bacterial enteric pathogens.