Brucella abortus HtrA functions as an authentic stress response protease but is not required for wild-type virulence in BALB/c mice

A second mutation has recently been identified in the previously described Brucella abortus htrA mutant PHE1. As a result of this finding, a new B. ab ortus htrA mutant, designated RWP11, was constructed to evaluate the biolog ical function of the Brucella HtrA protease. RWP11 is more sensitive to oxi dative killing in vitro and less resistant to killing by cultured murine ne utrophils and macrophages than the virulent parental strain 2308 but is not attenuated in BALB/c mice through 4 weeks postinfection. The in vitro phen otype of B. abortus RWP11 is consistent with the proposed function of bacte rial HtrA proteases as components of a secondary line of defense against ox idative damage. The in vivo phenotype of this mutant, however, indicates th at, unlike the corresponding Salmonella and Yersinia proteins, Brucella Htr A does not play a critical role in virulence in the mouse model.