In vitro and in vivo cholera toxin production by classical and El Tor isolates of Vibrio cholerae.

A comparative study was carried out on the in vitro production of cholera toxin by 19 Vibrio cholerae El Tor isolates from patients with cholera in South Africa, one El Tor isolate from a patient in Malawi (a country approximately 1000 km north-northeast of South Africa), 6 El Tor and 12 classical type isolates from patients in Bangladesh, and 5 culture collection classical strains. Identical phage types and indistinguishable toxigenicities among the South African and Malawi V. cholerae, representing isolations obtained over a 10-year period, indicated that essentially a single strain was involved in the cholera of these regions. Similarly, phage typing and toxin profiles indicated that the 12 classical and 6 El Tor V. cholerae cultures in Bangladesh, all isolated in November 1983, represented just two strains. As assessed by titrations in Y-1 mouse adrenal and Chinese hamster ovary cell lines, the general order of toxigenicities was Bangladesh and culture collection classical greater than Bangladesh El Tor greater than southern African El Tor. The African isolates consistently gave rise to very low titers. Their relative reluctance to produce the toxin in vitro compared with the culture collection classical strains, particularly strain 569B, was confirmed by rocket electrophoresis. In somewhat of a contrast, maximum in vivo titers in rice water stools from cholera patients in South Africa and from both classical and El Tor type cholera patients in Bangladesh were essentially equal. It is postulated that under the continuous culture conditions that occur in vivo, cholera toxin concentrations can accumulate to a maximum level, depending on the rate of purging by the diarrheal fluid rather than the toxigenicity of the infecting stain. The relevance of these findings to the relative severities of classical and El Tor types of cholera is discussed.

Haemagglutination patterns of diarrhoea-associated Escherichia coli strains in South Africa.

Using erythrocytes from six mammalian species, haemagglutination studies of 106 Escherichia coli isolates from infants with diarrhoea yielded fifteen different patterns. Although similar distribution patterns occurred between broth and agar grown cultures, individual strains often did not show identical patterns with the two methods of propagation. The complexity of patterns and medium-dependent variation of strains support the view that haemagglutination alone is not a suitable method for the demonstration of pili antigens. Furthermore, electron microscopy revealed pilus-like structures on the surface of only 21 out of 31 strains (66%) demonstrating positive haemagglutination. This finding is in accordance with the claim that surface antigens which are not derived from conventional pili may be responsible for attachment.

Variance in rotavirus infection rates in different urban population groups in South Africa.

Rotavirus infection in black infants contrasts markedly with that of white infants in being much less common and showing no seasonal variation. In this multicentre study in Johannesburg, the aetiology of winter infantile gastroenteritis in black, coloured, and white infants was investigated. Stools were examined by electron microscopy and also by enzyme-immunoassay to detect subparticular antigen which may be missed by electron microscopy in patients presenting late in the course of the illness. Stools were also examined bacteriologically by conventional techniques. Rotavirus was the most common pathogen in all three population groups with bacteria playing a relatively minor role. Striking differences were observed in the rotavirus rates between the three groups. Infection in the whites was five times more common than in the blacks (60% versus 12%) with the coloureds intermediate at 40%. The hypothesis was put forward that the relative protection of the black population may be due to a greater degree of colonization of neonates, thus inducing protection against symptomatic infection at the target age of 6 to 24 months. This may well have important implications in immunoprophylaxis. The reason for the lack of seasonal variation in the black population is still unclear.

Summer diarrhoea in African infants and children.

Of 70 black South African infants and children with acute summer diarrhoea, 30 (43%) were infected with enteropathogenic serogroups of Escherichia coli (EPEC), 13 (19%) with enterotoxigenic Gram-negative bacilli, 12 (17%) with Salmonella sp., 6 (9%) with Shigella sp., and 3 (4%) with rotaviruses. 13 (19%) patients were infected simultaneously with more than one enteropathogen, and no pathogen was detected in 22 (31%). In addition, 6 (15%) of 41 unselected patients were excreting Campylobacter fetus. Of 30 age-matched controls drawn from the same population, 5 (17%) were infected with EPEC serotypes, and 1 each with Salmonella sp. and rotavirus. This study stresses the polymicrobial nature of paediatric diarrhoea in a developing community and shows the continued importance of EPEC in this setting.

Mechanism of action of Yersinia enterocolitica enterotoxin.

Enterotoxin derived from three clinical isolates of Yersinia enterocolitica was compared with the heat-stable enterotoxin of Escherichia coli. Both toxins were biologically active in infant mice examined at 2 h and in ligated rabbit ileal loops at 6 h. Neither substance, however, produced changes in ligated ileal loops at 18 h or in Chinese hamster ovary or Y1 adrenal tissue cultures. In addition, both Y. enterocolitica enterotoxin concentrated approximately 20 times by ammonium sulfate precipitation and ultrafiltration and a similarly prepared sample of E. coli heat-stable enterotoxin stimulated the activity of guanylate cyclase but not that of adenylate cyclase in infant mouse intestine. These findings suggest that the role of enterotoxin in the pathogenesis of intestinal Y.enterocolitica infection may be similar to that of heat-stable enterotoxin in E. coli diarrhea.

The pathogenesis of Yersinia enterocolitica gastroenteritis.

Of nine Y. enterocolitica serotypes examined by us, only type 3 was shown to be enteropathogenic. 3 of 16 strains recovered from clinical material, produced a heat-stable toxin similar to that reported in E. coli. A fourth isolate produced histological changes resembling those associated with salmonellae. The mechanism whereby the majority of Y. enterocolitica strains produce diarrhoea is uncertain. Our isolates may have lost a plasmid essential for enteropathogenicity, or they may resemble the 'classical' enteropathogenic strains of E. coli for which no satisfactory experimental model exists. Further studies on freshly isolated strains are in progress in order to determine the prevalence of enterotoxigenic Y. enterocolitica.

Rotavirus and winter gastro-enteritis in White South African infants.

In a microbiological investigation of winter gastro-enteritis in 23 White children rotaviruses were found in 14 (61%) and parvovirus-like particles in 1 (4%). Bacteriological examination of stools from 11 of these patients yielded one isolate of Salmonella eastbourne, but no enterotoxigenic or invasive bacteria were found. Rotavirus appears to be the main aetiological agent of acute winter gastro-enteritis in White infants.

Pathogenic mechanisms of a non-agglutinable Vibrio cholerae strain: demonstration of invasive and enterotoxigenic properties.

A non-agglutinable Vibrio cholerae strain isolated from the blood of a child with kwashiorkor and fever was shown to have the potential to invade as well as to produce a toxin resembling cholera toxin.