Academic journal article Journal of Health Population and Nutrition

Molecular Epidemiology of Escherichia Coli Isolated from Young South African Children with Diarrhoeal Diseases

Academic journal article Journal of Health Population and Nutrition

Molecular Epidemiology of Escherichia Coli Isolated from Young South African Children with Diarrhoeal Diseases

Article excerpt

INTRODUCTION

Escherichia coil is a normal faecal flora of both humans and animals. However, some strains of E. coli can cause severe and life-threatening diarrhoea (1). The pathogenic strains are important causes of diarrhoeal disease in the world and remain a major public health problem of children and young infants (2). Although the use of oral rehydration therapy has reduced early childhood mortality caused by acute dehydrating diarrhoeas in many developing countries, persistent diarrhoea still remains an important cause of mortality due to diarrhoeal diseases (3).

Some of the E. coli strains have been reported to possess a battery of virulence determinants which enable them to overcome the host's defense mechanisms and produce disease. The well-characterized virulence factors to date are: P-fimbriae, type 1 fimbriae, haemolysin, aerobactin, and serum resistance (4,5). The polysaccharides of O and K antigens protect the organism from the bactericidal effects of complement and from phagocytosis in absence of specific antibodies (6).

Adhesion has also been shown to be an important virulence factor of E. coli (7). This has led to tissue culture adherence assays to identify pathogenic strains of E. coli. Three patterns of adherence have been described (8): localized adhesion characterized by the formation of bacterial microcolonies, diffuse adhesion in which bacteria cover the cell surface uniformly, and aggregative adhesion in which clumps of bacteria with a stacked brick appearance are found on the surface of the cells. Other virulence factors that contribute to the pathogenicity of this organism are the production of enterotoxins, cytotoxins, bundle-forming pili, cytotoxic necrotizing factors, enteropathogenic and effacement factors, and Shiga-like toxins.

Several distinct groups of E. coli which include the enteropathogenic, enteroinvasive, enteroaggregative, enterotoxigenic, Shiga toxin-producing and necrotizing strains are important causes of diarrhoeal diseases in developing countries (9,10). These strains differ in their serotypes (O:H), pathogenesis, and characteristics of the resulting disease, including clinical presentation and epidemiology (2,11,12). However, the importance of these organisms as diarrhoeal pathogens and their molecular characteristics in South African population are unknown.

This community survey was conducted to define the molecular epidemiology of diarrhoeagenic strains of E. coli in the Gauteng region of South Africa.

MATERIALS AND METHODS

Patients

In total, 109 faecal samples from patients with diarrhoea presenting at the Ga-Rankuwa Hospital between March 1996 and May 1997 were collected. An additional 36 E. coli strains, isolated from patients with diarrhoea, were obtained from the Helen Joseph Hospital, Pretoria Academic Hospital, Du Buisson, and van Drimmelen private pathology laboratories in Gauteng province.

Thirty fresh faecal specimens were collected from a control group of healthy individuals from the same population in different settings. Patients and controls belonged to different age groups ranging from 3 days to 64 years. All patients had symptoms of diarrhoea. Additional information about these patients is given in Table 1.

Reference strains

Reference strains used in this study included: C600 (933J) for Shiga toxin (Stx1), C600 (933W) for Shiga toxin 2 (Stx2), BM2-1 cytotoxic necrotizing factor (CNF) 1, and B20A for CNF (CNF2). Reference strains were provided by J. de Rycke, Station de Pathologie de la Reproduction, Nouzilly, France (strain BM2-1); J. Blanco, Facultad de Veterinaria, Lugo, Spain (strain B20A), A.D. O'Brien, Department of Microbiology, Uniform Services University of the Health Sciences, Bethesda, MD, USA [strains C600 (933J) and (933W)].

Identification of E. coli

Bacterial cultures of stool specimens from the patients and from the control group were performed by inoculating stools on standard MacConkey plates containing lactose and sorbitol separately. …

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