A motility lesion in ColV+ Escherichia coli strains and its possible clinical significance

Virulence factors of Escherichia coli serotypes associated with avian colisepticaemia

The current understanding of the pathogenesis of avian pathogenic Escherichia coli (APEC) in colisepticaemia is limited. This review discusses putative virulence determinants per se, such as a number of surface organelles including fimbriae and flagella; together with other factors such as iron sequestering mechanisms, which are involved in the survival of E. coli in the host rather than initiation of infection. It is concluded that avian colisepticaemia is a multi-factorial disease and that to date only a limited number of virulence factors of APEC have been thoroughly elucidated.

Preservative-mediated changes of the surface properties of Escherichia coli

The effectiveness of two commonly used preservatives, sodium benzoate and potassium disulfite, was evaluated in terms of their bactericidal activity and capacity to induce changes in the surface properties of Escherichia coli isolated from commercial food preserves. Preservative treatment over a five-week test period resulted in controlling the multiplication of these organisms and causing a decline in cell-surface hydrophobicity, hemagglutinating ability and adherence capacity to rat intestinal cells of E. coli isolates. A loss in motility was also exhibited.

Microbial contamination of weaning foods

A survey was conducted to determine the prevalence rate of Escherichia coli in different foods being fed to children in the weaning age group. The samples were collected from middle income group (MIG) and high income group (HIG) houses in different localities in Chandigarh. A total of 530 MIG and 525 HIG houses were selected on the basis of availability of children in the weaning age group. A total of 2,016 samples of weaning foods were collected. Isolation of Escherichia coli from MIG and HIG houses was 66.75% and 8.5% respectively. Enterotoxigenic Escherichia coli were detected in 61.47% and 43.5% of the total Escherichia coli isolates from MIG and HIG houses respectively. 'O' serogrouping of the isolates was done and the predominant serotypes found were 06, 0106, 043, 057, 01. The laboratory studies showed that almost all weaning food samples prepared in the laboratory supported the growth of known enterotoxigenic Escherichia coli.

Colicin V virulence plasmids

ColV plasmids are a heterogeneous group of IncFI plasmids which encode virulence-related properties such as the aerobactin iron uptake system, increased serum survival, and resistance to phagocytosis. These plasmids have been found in invasive strains of Escherichia coli which infect vertebrate hosts including humans and livestock. Colicin V was the first colicin to be identified, in 1925, but not until the field experienced a renewed interest has the mechanism of colicin V activity been explored. As encoded by ColV plasmid pColV-K30, the aerobactin iron uptake system has been extensively investigated, but other ColV-encoded phenotypes remain largely uncharacterized. Restriction enzyme mapping of the 144-kb pColV-K30 and of the 80-kb pColV-B188 has facilitated systematic study, so that questions can be addressed by a molecular and comparative approach regarding the contributions of individual factors and plasmids to the virulence of host E. coli in model systems. The family of large ColV plasmids could be analogous to other families of large virulence plasmids, and insights gained from studying these plasmids should contribute to our understanding of cross-genetic interactions and the role of large plasmids in bacterial pathogenesis.

Virulence factors in Escherichia coli urinary tract infection

Uropathogenic strains of Escherichia coli are characterized by the expression of distinctive bacterial properties, products, or structures referred to as virulence factors because they help the organism overcome host defenses and colonize or invade the urinary tract. Virulence factors of recognized importance in the pathogenesis of urinary tract infection (UTI) include adhesins (P fimbriae, certain other mannose-resistant adhesins, and type 1 fimbriae), the aerobactin system, hemolysin, K capsule, and resistance to serum killing. This review summarizes the virtual explosion of information regarding the epidemiology, biochemistry, mechanisms of action, and genetic basis of these urovirulence factors that has occurred in the past decade and identifies areas in need of further study. Virulence factor expression is more common among certain genetically related groups of E. coli which constitute virulent clones within the larger E. coli population. In general, the more virulence factors a strain expresses, the more severe an infection it is able to cause. Certain virulence factors specifically favor the development of pyelonephritis, others favor cystitis, and others favor asymptomatic bacteriuria. The currently defined virulence factors clearly contribute to the virulence of wild-type strains but are usually insufficient in themselves to transform an avirulent organism into a pathogen, demonstrating that other as-yet-undefined virulence properties await discovery. Virulence factor testing is a useful epidemiological and research tool but as yet has no defined clinical role. Immunological and biochemical anti-virulence factor interventions are effective in animal models of UTI and hold promise for the prevention of UTI in humans.

Aerobactin production as a virulence factor: a reevaluation

Iron starvation is one of the major barriers that virulent bacteria must overcome in order to proliferate in the host. Virtually all microorganisms possess high affinity iron (III) transport systems mediated by low molecular weight iron specific chelators called siderophores, the synthesis of which is activated under iron-limiting conditions. Siderophore aerobactin is frequently produced by enterobacteria which cause various types of infections in humans and animals. The status of aerobactin production as a virulence factor is evaluated both from data derived from experimental infection systems and the actual presence of this siderophore in clinical isolates. Aerobactin appears to be an important contributor to extracellular pathogenesis (mostly, that of Escherichia coli strains causing septicaemia and urinary tract infections) and to the extracellular stages of growth of intracellular pathogens like Shigella. When invasive bacteria actually enter target cells, acquisition of iron seems to occur independently of siderophore production. The feasibility of an antimicrobial therapy aimed at interfering with siderophore functioning is discussed.

Resistance of attached Escherichia coli to acrylic acid and its significance for the survival of plasmid-bearing organisms in water

As previously reported, free organisms of Escherichia coli are sensitive to damage and killing when exposed to acrylic acid in water. The effect of the agent was greatest in distilled water, but there was a marked effect in effluent and seawater also. The effect was temperature-dependent, with organisms exposed at 4 degrees C being much less affected than those exposed at 20 degrees C. The above sensitivity was for free organisms, but those attached to glass beads were resistant to acrylate. This resistance applied equally to attached plasmid-free and attached plasmid-bearing organisms, but is likely to be more significant for plasmid-bearing strains because some plasmids studied here stimulated bacterial attachment. The likely significance of the acrylate resistance of attached organisms for enterobacterial survival in the aquatic environment, e.g. in the vicinity of shellfish beds, is discussed.

Virulence plasmid-associated adhesion of Escherichia coli and its significance for chlorine resistance

Introduction of the ColV, I-K94 virulence plasmid into strains of Escherichia coli led (for four out of five strains tested) to a marked increase in the ability of organisms to adhere to glass beads. For strain 1829, the plasmid led to increased attachment to other materials including sand, agar, agarose, chitin and cellulose. The increased adhesion to glass beads was due to the presence of the plasmid and not to its introduction into a variant with altered adhesive properties. The plasmid-encoded VmpA protein did not appear to be necessary for the ColV, I-K94-promoted adhesion but adhesion was absolutely dependent on the presence of derepressed levels of transfer components in the ColV+ strains and partially dependent on the presence of colicin components. The extent of the plasmid-promoted adhesion was greatest for organisms grown at 30 degrees, 37 degrees or 42 decrees C and adhesion was almost abolished by growth at 21 degrees or 25 degrees C; this finding is in accord with transfer and colicin components being involved in adhesion. Of several other plasmids tested for their effects on adhesion, those with derepressed transfer properties showed a marked effect as did the RI resistance plasmid. Because of the ease of handling glass bead-attached organisms, such preparations were used as a model for studying the relevance of attachment to the resistance of E. coli to chlorination in the water purification process. Organisms of 1829 ColV, I-K94, attached to glass beads, were more resistant to damage and killing by chlorine than were unattached organisms. Three findings suggest that such chlorine resistance may be significant for survival during water chlorination. Firstly, ColV, I-K94+ bacteria became attached if incubated in sewage effluent with glass beads at 20 degrees C. Secondly, ColV+ organisms already attached to glass beads maintained their attachment during 24 h incubation in effluent at 20 degrees C and thirdly such effluent incubated organisms remained chlorine resistant provided that they retained their attachment.