Flagella and pili as antigenically variable structures on the bacterial surface

Use of temporal temperature gradient gel electrophoresis to identify flaA and fim3 sequence types in Bordetella bronchiseptica

AIMS

The aim of this study was to develop an approach to detect variation in the flaA and fim3 genes amongst animal isolates of Bordetella bronchiseptica using temporal temperature gradient gel electrophoresis (TTGE).

METHODS AND RESULTS

Amplicons representing three flaA and two fim3 sequence types were subjected to TTGE analysis. It was possible to distinguish clearly between each of the sequence types using TTGE.

CONCLUSION

This suggests that TTGE could be a useful tool for studying the epidemiology of B. bronchiseptica.

SIGNIFICANCE AND IMPACT OF THE STUDY

PCR amplification coupled to TTGE offers a general method for the rapid screening of large numbers of microbial strains for variations in gene sequences.

Serological and molecular size characterization of flagellins of Pseudomonas syringae pathovars and related bacteria

Flagella from a total of 118 strains representing mostly pathovars of the phytopathogenic group Pseudomonas syringae, but also P. chlororaphis, P. cichorii, P. corrugata, P. fluorescens, P. fuscovaginae, P. stutzeri, P. viridiflava, as well as related phytopathogenic genera (Burkholderia cepacia and Ralstonia solanacearum) were characterized by immuno-fluorescent staining, SDS-PAGE, and immunoblotting. Eighty-six strains of the P. syringae group pathovars, P. cichorii and P. viridiflava were shown to possess flagella of serotypes H1 or H2, composed of a unique flagellin, whose molecular size varied between 31 and 31.5 kDa. Similarities between the P. syringae flagellin and a 31 kDa surface protein involved in pathogenicity are pointed out. The distribution of H1 and H2 antigens in the nine recently described genomospecies of P. syringae-P. viridiflava group suggested that flagellin would represent a phylogenetic marker within the arginin-dihydrolase-negative fluorescent pseudomonads. The characterization of flagellin was proposed as an identification tool at a level situated between genus and species.

A novel mechanism of phase variation of virulence in Staphylococcus epidermidis: evidence for control of the polysaccharide intercellular adhesin synthesis by alternating insertion and excision of the insertion sequence element IS256

Biofilm formation of Staphylococcus epidermidis on smooth polymer surfaces has been shown to be mediated by the ica operon. Upon activation of this operon, a polysaccharide intercellular adhesin (PIA) is synthesized that supports bacterial cell-to-cell contacts and triggers the production of thick, multilayered biofilms. Thus, the ica gene cluster represents a genetic determinant that significantly contributes to the virulence of specific Staphylococcus epidermidis strains. PIA synthesis has been reported recently to undergo a phase variation process. In this study, biofilm-forming Staphylococcus epidermidis strains and their PIA-negative phase variants were analysed genetically to investigate the molecular mechanisms of phase variation. We have characterized biofilm-negative variants by Southern hybridization with ica-specific probes, polymerase chain reaction and nucleotide sequencing. The data obtained in these analyses suggested that in approximately 30% of the variants the missing biofilm formation was due to the inactivation of either the icaA or the icaC gene by the insertion of the insertion sequence element IS256. Furthermore, it was shown that the transposition of IS256 into the ica operon is a reversible process. After repeated passages of the PIA-negative insertional mutants, the biofilm-forming phenotype could be restored. Nucleotide sequence analyses of the revertants confirmed the complete excision of IS256, including the initially duplicated 8 bp target sites. These results elucidate, for the first time, a molecular mechanism mediating phase variation in staphylcocci, and they demonstrate that a naturally occurring insertion sequence element is actively involved in the modulation of expression of a Staphylococcus virulence factor.

Shared themes of antigenic variation and virulence in bacterial, protozoal, and fungal infections

Pathogenic microbes have evolved highly sophisticated mechanisms for colonizing host tissues and evading or deflecting assault by the immune response. The ability of these microbes to avoid clearance prolongs infection, thereby promoting their long-term survival within individual hosts and, through transmission, between hosts. Many pathogens are capable of extensive antigenic changes in the face of the multiple constitutive and dynamic components of host immune defenses. As a result, highly diverse populations that have widely different virulence properties can arise from a single infecting organism (clone). In this review, we consider the molecular and genetic features of antigenic variation and corresponding host-parasite interactions of different pathogenic bacterial, fungal, and protozoan microorganisms. The host and microbial molecules involved in these interactions often determine the adhesive, invasive, and antigenic properties of the infecting organisms and can dramatically affect the virulence and pathobiology of individual infections. Pathogens capable of such antigenic variation exhibit mechanisms of rapid mutability in confined chromosomal regions containing specialized genes designated contingency genes. The mechanisms of hypermutability of contingency genes are common to a variety of bacterial and eukaryotic pathogens and include promoter alterations, reading-frame shifts, gene conversion events, genomic rearrangements, and point mutations.

Electron microscopic examination of factors influencing the expression of filamentous surface structures on clinical and environmental isolates of Aeromonas veronii Biotype sobria

Strains of Aeromonas veronii biotype sobria isolated from clinical and environmental sources were examined for their expression of surface structures under a variety of culture conditions. When grown on solid media at 37 degrees C, more than 95% of bacteria from the majority of strains isolated from human diarrheal feces and chicken carcasses were non-piliated or expressed only a few pili of long, flexible morphology per cell. Strains isolated from water or other foods were much more likely to express pili. Heavily piliated strains (all sources) possessed pili of several morphological types, including long, flexible pili of varying widths and rigid pili of varying lengths. Expression of Pili was favored by growth at temperatures ca. 20 degrees C and below and growth in liquid medium. Most fecal strains expressed some pili under these conditions. In addition, other surface structures (fibrillar aggregates, fibrillar networks bundle-forming pili) were seen on some strains from most sources. These were also seen most frequently when bacteria were grown in liquid media at temperatures ca. 20 degrees C and below. Pili expression was not dramatically influenced by growth under anaerobic conditions, or in iron-depleted media, or by combinations of the above conditions. The role of the above surface structures in Aeromonas pathogenicity remains to be elucidated.