Virulence of Pasteurella multocida recA mutants

In order to determine the role of the RecA protein in the virulence of Past eurella multiocida, a recA mutant was constructed and used in studies of vi rulence and competition in relation to wildtype strain. To achieve this, fi rstly, the recA gene was isolated and sequenced, showing an Escherichia cal l-like SOS box and encoding a protein of 354 amino acids which has the clos est identity with the Haemophilus influenzae RecA protein. Further, the rec A mutant was constructed, by inactivating this gene by single recombination of a suicide plasmid containing an internal region of the P. multocida rec A gene, and shown to be more sensitive to W radiation than the parental str ain. The P multocida mutant was slightly attenuated in virulence, as indica ted by the LD50, the time of death of infected animals, and a failure to co mpete with the wild-type strain in mixed infections. Compared to the parent strain, the mutant had a similar growth rate but a longer lag phase. These data suggest that the diminished virulence of the recA mutant as well as i ts failure in competition were more a consequence of the long lag phase rat her than a direct effect of the inactivation of the recA gene on genes invo lved in virulence. (C) 2001 Elsevier Science B.V. All rights reserved.