Impact of recombinant DNA technology on studies of bacterial pathogenicity.

Gene manipulation techniques along with other molecular approaches have aided studies on bacterial pathogenicity in a number of ways. Potential virulence determinants have been isolated from a wide variety of pathogenic bacteria and some of these have been characterized in order to determine their genetic organization and identify specific gene products. Proteins such as toxins, adhesins, extracellular enzymes and surface antigens have been analysed. Once a potential virulence determinant has been characterized opportunity exists for further manipulations to be undertaken. For example, natural toxoid producing strains have been constructed including organisms expressing high levels of E. coli heat-labile toxin B-subunit and cholera B-subunits. Gene fragments can be used as hybridization probes to screen for silent or related virulence genes. Mutated genes can be re-introduced into parental pathogenic bacteria, following manipulations in E. coli, to construct specific mutants. Examples of some of these approaches will be discussed.