Envelope protein changes, autoagglutination, sensitivity to hydrophobic agents and a conditional division lesion in Escherichia coli strains carrying ColV virulence plasmids

Morphological changes to Escherichia coli O157:H7, commensal E. coli and Salmonella spp in response to marginal growth conditions, with special reference to mildly stressing temperatures

Certain rod-shaped bacteria have been reported to form elongated filamentous cells when exposed to marginal growth conditions, including refrigeration temperatures. To expand upon these observations, the filamentation of commensal Escherichia coli, E. coli O157:H7 and Salmonella spp was investigated, following exposure to certain, mildly stressing, levels of temperature, pH or water activity (aw), with levels of cellular protein being monitored during cell elongation, in some experiments. Our studies indicated that cellular filamentation could be demonstrated in all 15 strains of the above organisms tested, following exposure to marginal conditions achieved by incubation at high or low temperatures, high or low pH values and low aw. The level of environmental stress causing filamentation tended to be specific to the particular organisms. For example, Salmonella spp formed filamentous cells at 44 degrees C, whereas E. coli strains, including O157, grew by binary fission at that temperature, but formed filamentous cells at 46 degrees C. In addition, plate count techniques to enumerate bacteria during filamentation, failed to reflect the increase in cell biomass that was occurring, whereas measurements of protein concentration demonstrated the increase quite strikingly. These findings have important implications for our understanding of the ability of food-borne pathogens to cause disease, since the infectious dose of a microorganism implicated in an outbreak of such disease is typically determined by a viable count method, which could underestimate the number of potential infectious units present in a food that had been stored in such a way as to provide marginal growth conditions.

UV radiation-induced enterobacterial responses, other processes that influence UV tolerance and likely environmental significance

The ability of enterobacteria to become UV-tolerant is important because such tolerance may enable organisms to resist irradiation in the environment, in water treatment, in shell-fish, in stages of food processing, and at locations in the domestic, commercial and hospital environment The mechanism for regulation of tolerance induction and SOS response induction has been studied for many years, and is well understood, except for the early stages of induction. Such early stages, namely sensing of the stimulus (UV irradiation) and the way in which such sensing leads to signal production, have until now been poorly understood. The claim has been made that DNA is the sensor and that either damage to DNA or production of SS regions in DNA (following interaction of UV with DNA) triggers the signal that sets in train RecA activation and other stages of tolerance induction. This claimed induction mechanism is a "classical" one in the sense that it involves intracellular sensing (by DNA) of the stressing stimulus (UV), and production of an intracellular signalling molecule. It is not, however, firmly established as the mechanism for initiation of UV tolerance induction and SOS response induction. The results reviewed here give firm evidence for a different and unique mechanism for sensing of UV and production of the signal. These results establish without doubt that, for UV tolerance induction, the UV sensor is an extracellular protein, which is a UV tolerance-specific extracellular sensing component (ESC). This component is formed by unstressed cells and on interacting with the stimulus (UV) in the medium, is converted to the tolerance induction signalling molecule, which is a UV tolerance-specific extracellular induction component (EIC). It is this extracellular signal which interacts with the sensitive organisms and triggers tolerance induction. This pair of extracellular components (ECs) may offer the only means of switching-on such tolerance induction; certainly they offer the only known way for early warning to be given of impending UV challenge. Thus, the EIC can diffuse from a region of UV stress to a stress-free region and there warn organisms of impending stress and prepare them to resist it. As indicated here, UV irradiation not only induces UV tolerance, but also switches-on acid tolerance, alkali tolerance and thermotolerance responses. The fact that all three responses involve ESC/EIC pairs strongly supports the view that functioning of such EC pairs form the major, if not the only, means for UV tolerance induction. The UV tolerance-specific ESC can detect other stresses and becomes activated, leading to cross-tolerance responses. Of particular interest, this ESC acts as a biological thermometer, detecting increases in temperature, such increases leading to gradually increasing formation of the EIC and, accordingly, gradual increases in UV tolerance. This UV tolerance-specific ESC can also detect other stresses e.g. acting as a pH sensor. In all cases, on activation, the EIC formed (from this specific ESC) only induces UV tolerance. It is proposed that the interaction of EICs with stress-sensitive organisms should be examined, and it is suggested that such EICs may, directly or indirectly, interact with and activate the same stress response regulators as are used to detect internal stressors and which, on activation, also trigger the switching-on of stress responses. For example, EICs either a in a protonated or oxidised state (formed by activation of ESCs by H+ or H2O2) or b produced by irradiation, may lead to protonation or oxidation or other forms of activation of the appropriate regulator (e.g. Fur or OxyR or RecA etc), leading to response induction.

Clonal relationships among Escherichia coli serogroup O78 isolates from human and animal infections

We investigated the clonal relationships among 63 Escherichia coli strains of antigen serogroup O78 isolated from infections in humans, cattle, sheep, pigs, and chickens. Both septicemic and enterotoxigenic isolates were included in the study. A main group of 55 E. coli strains consisting of 52 septicemic isolates and 3 human enterotoxigenic E. coli isolates were clustered in related clones. The remaining eight strains, four human and four animal isolates, were clonally heterogeneous. The main group of 55 clonally related strains included isolates from human and animal infections. This result indicates that animals are a possible source of serogroup O78 septicemic E. coli infections in humans.

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.

Influences of conjugal genetic transfer functions of colicin V plasmids on adhesion of Escherichia coli to murine intestinal tissue

Cells of strains of Escherichia coli K-12 291 bearing one of three colicin V plasmids, pF54, pH247, or pF70, were tested in comparison with cells of strain 291 for their ability to adhere to murine intestinal tissue in vitro. The plasmids were either repressed or derepressed in conjugal genetic transfer functions. The strains bearing pF54 and pH247 repressed in transfer functions (pColVF54 luminal diameter r and pColVH247 luminal diameter r) adhered in higher numbers to the murine tissue than did the host strain lacking the plasmid or the strains containing the plasmids with active transfer functions (pColVF54drd and pColVH247drd). The number of cells (CFU) of strain 291(pColVF54 luminal diameter r) adherent to the tissue was related directly to the time of incubation (up to 30 min) and to the number of cells (CFU) to which the tissues were exposed. As indicated by tests for sensitivity to F factor (F)-pilus-specific bacteriophages, the cells of strains bearing the plasmids derepressed for conjugal functions had F pili on their surfaces, while such structures were missing from cells of the parental strain (291) and the strains containing the plasmids in repressed form. This finding was supported by transmission electron microscopy of cells of strain 291, 291(pColVF54 luminal diameter r), and 291(pColVF54drd). F pili could be seen on cells of the latter strain but not on those of the parental strain or the strain bearing pColVF54 luminal diameter r. Pili other than F pili were not seen on cells of the strains bearing pF54 in either form. Strains 291(pColVF70drd) and 291(pColVF70 luminal diameter r) adhered to the tissues in numbers comparable to those of strain 291. Nevertheless, these findings are further evidence that for certain colicin V plasmids (A. M. Nilius and D. C. Savage, Infect. Immun. 43:947-953, 1984), conjugal genetic transfer functions influence properties that may be important in the pathogenesis of invasive E. coli strains.

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.

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

The introduction of the ColV-K30 or ColV,I-K94 plasmid into Escherichia coli strains produced derivatives which had a motility lesion if grown without shaking at 37 degrees C. Although most ColV+ organisms from shaken cultures were motile, 80-90% of free unclumped organisms from static cultures were flagellate but non-motile. This plasmid effect was temperature-dependent with only those ColV+ organisms grown at 37 degrees C being affected; ColV+ organisms grown at 30 degrees C or below were predominantly motile. The motility lesion depended on the presence, in the ColV+ organisms, of transfer and colicin components together but not of the VmpA protein. Aside from the changed motility, there was extensive autoagglutination (clumping) of ColV+ organisms in static cultures, and the two phenomena (clumping and motility lesion) appeared to be governed by the same factors. The Flac plasmid of FI incompatibility group had a slight inhibitory effect on motility of strain 1829 and caused slight clumping, but representative plasmids of groups FII, FIII, FIV, C, H, I, K, M, N, P, W and X had no appreciable effect on either parameter. Non-motile ColV+ organisms regained motility on incubation with buffered detergent solutions, suggesting that an envelope change might be responsible for the altered motility. It can be hypothesized that ColV+ organisms in the intestine would be motile and hence able to reach the intestinal epithelium for invasion but that, once such organisms had reached the tissues and bloodstream, they would be predominantly non-motile and hence might be less susceptible to phagocytosis.