A novel antioxidant gene from Mycobacterium tuberculosis.

Among the major antimicrobial products of macrophages are reactive intermediates of the oxidation of nitrogen (RNI) and the reduction of oxygen (ROI). Selection of recombinants in acidified nitrite led to the cloning of a novel gene, noxR1, from a pathogenic clinical isolate of Mycobacterium tuberculosis. Expression of noxR1 conferred upon Escherichia coli and Mycobacterium smegmatis enhanced ability to resist RNI and ROI, whether the bacteria were exposed to exogenous compounds in medium or to endogenous products in macrophages. These studies provide the first identification of an RNI resistance mechanism in mycobacteria, point to a new mechanism for resistance to ROI, and raise the possibility that inhibition of the noxR1 pathway might enhance the ability of macrophages to control tuberculosis.

HEp-2 cell adherence and Vero cell cytotoxin production by EPEC strains isolated from children with diarrhoea in New Zealand.

A total of 112 EPEC strains isolated from children with diarrhoea in New Zealand were examined for mannose-resistant HEp-2 cell adherence and production of exotoxins. Enterotoxin production was not detected in any of the strains examined. Verotoxin production was detected in 13 (11.6%) strains and of these 4 were also found to adhere to HEp-2 cells. HEp-2 cell adherence was displayed by a total of 29 (25.8%) strains of which 22 were diffusely adherent. Only 3 (2.7%) strains were shown to belong to the new virulence phenotype, entero-aggregative adherence, when examined in the adherence assay. We identified one strain with the novel characteristic of causing detachment of HEp-2 cells from glass coverslips and are further investigating this possible virulence mechanism. These results suggest that if EPEC strains are to be considered as a cause of diarrhoea, the search for new virulence factors must be extended.

Sorbose fermentation in relation to acquisition and maintenance of enterotoxin plasmids in Escherichia coli.

Previous studies have shown that the majority of enterotoxigenic Escherichia coli (ETEC) strains isolated from humans failed to ferment sorbose. In an attempt to demonstrate if this phenomenon was due to enterotoxin (Ent) plasmid instability in sorbose fermenting strains, recipient E. coli strains were used in conjugation experiments with three donor Ent plasmids. No difference in the ability to uptake the Ent plasmid was shown between sorbose fermenting and non-fermenting recipient strains. In addition, no difference was seen in the stability of the Ent plasmids in recipient strains of each biotype. These results suggest that in-vivo selection may play a role in the predominant isolation of non-sorbose fermenting ETEC strains.

Virulence factors associated with strains of Escherichia coli from cases of sudden infant death syndrome (SIDS).

Strains of Escherichia coli isolated from cases of Sudden Infant Death Syndrome, healthy infants and infants that died of other causes were subjected to a series of tests with particular reference to serotyping, toxigenicity and adherence factors. E. coli from SIDS infants tended to have a low hydrophobicity and high toxigenicity, compared to those from healthy infants, while no notable differences in haemagglutination patterns were observed between these two groups of strains.

Epidemiology and microbiology of diarrhoea in young Aboriginal children in the Kimberley region of Western Australia.

Infectious diarrhoea is common in young Australian Aborigines and is one of the main causes for their unsatisfactory health standards with consequent widespread failure to thrive and undernutrition. Most published reports relate to patients in hospital or to hospital admission statistics and give little indication of the extent or severity of diarrhoeal disease in children in Aboriginal communities. The present investigation involved more than 100 Aboriginal children up to 5 years of age living in remote communities in the tropical north of Western Australia who were studied prospectively over a 12-month period.

Identification of enteropathogenic Escherichia coli by PCR-based detection of the bundle-forming pilus gene.

A rapid and simple method of detecting enteropathogenic Escherichia coli (EPEC) was developed. The procedure is based on amplifying by the PCR method a 326-bp region of the bundle-forming pilus gene of EPEC. The oligonucleotide DNA primers used in this procedure did not amplify DNA of any other bacterial enteropathogens tested. The procedure was 100% specific for EPEC strains that exhibit a characteristic pattern of attachment (localized adherence) to HeLa cells.

Virulence factors of enteric Escherichia coli in young Aboriginal children in north-west Australia.

Enterotoxigenic Escherichia coli (ETEC) were the most frequently identified enteric pathogens associated with diarrhoea in 0-5 year old Aboriginal children in tropical north-west Australia with an incidence similar to those from other tropical regions. Heat-stable toxin-producing (ST+) strains were associated with diarrhoea throughout the year but heat-labile toxin-producing (LT+) strains were more important in the monsoonal summer season. ST+ strains were commonest in children with diarrhoea between 6 and 18 months of age while LT+ strains were associated with diarrhoea in children aged 18-24 months. Vero-toxigenic E. coli (VTEC) which produced VT1, but not VT2, and enteroadherent (EAF+) E. coli were significant causes of diarrhoea, mainly in children below 18 months but without a seasonal pattern.

Diffuse and enteroaggregative patterns of adherence of enteric Escherichia coli isolated from aboriginal children from the Kimberley region of Western Australia.

Escherichia coli from 138 fecal samples from aboriginal children, in whom no other enteric pathogen was isolated (including enterovirulent E. coli), were examined for HEp-2 cell adhesion. Twenty-five (36.8%) of 68 children with diarrhea and 32 (45.7%) of 70 without diarrhea had diffusely adherent isolates, which were thus not associated with diarrhea (P > .25). However, after age stratification, children > or = 18 months showed a significant association of diffusely adherent E. coli with diarrhea (P < or = .05). Enteroaggregative E. coli were isolated from 12 children with diarrhea (17.6%) and 15 without diarrhea (21.4%); thus, there was no association with diarrhea (P > or = .5). Sixteen children with diarrhea (23.5%) and 6 without diarrhea (8.6%) carried isolates that caused detachment of the HEp-2 cell monolayer from the glass coverslip when examined in the adhesion assay and were significantly associated with diarrhea (P < or = .05). These isolates, termed cell-detaching E. coli, were different from all recognized classes of enterovirulent E. coli.

Characterization of the roles of hemolysin and other toxins in enteropathy caused by alpha-hemolytic Escherichia coli linked to human diarrhea.

Escherichia coli strains producing alpha-hemolysin have been associated with diarrhea in several studies, but it has not been clearly demonstrated that these strains are enteropathogens or that alpha-hemolysin is an enteric virulence factor. Such strains are generally regarded as avirulent commensals. We examined a collection of diarrhea-associated hemolytic E. coli (DHEC) strains for virulence factors. No strain produced classic enterotoxins, but they all produced an alpha-hemolysin that was indistinguishable from that of uropathogenic E. coli strains. DHEC strains also produced other toxins including cytotoxic necrotizing factor 1 (CNF1) and novel toxins, including a cell-detaching cytotoxin and a toxin that causes HeLa cell elongation. DHEC strains were enteropathogenic in the RITARD (reversible intestinal tie adult rabbit diarrhea) model of diarrhea, causing characteristic enteropathies, including inflammation, necrosis, and colonic cell hyperplasia in both small and large intestines. Alpha-hemolysin appeared to be a major virulence factor in this model since it conferred virulence to nonpathogenic E. coli strains. Other virulence factors also appear to be contributing to virulence. These findings support the epidemiologic link to diarrhea and suggest that further research into the role of DHEC and alpha-hemolysin in enteric disease is warranted.

Differentiation of pathogenic Escherichia coli strains in Brazilian children by PCR.

A PCR technique to differentiate pathogenic enteric Escherichia coli strains in a field setting was evaluated. Among 76 children with acute diarrhea, this technique identified 12 children (16%) with enterotoxigenic E. coli, 6 (8%) with enteropathogenic E. coli, and 1 (1%) with enteroinvasive E. coli infection. Compared with the conventional assays, the PCR method proved to be simpler, more rapid, and inexpensive and therefore suitable for application in a developing-country field setting.