Evaluation of an isogenic major outer membrane protein-deficient mutant inthe human model of Haemophilus ducreyi infection

Haemophilus ducreyi expresses 2 OmpA homologs, designated MOMP and OmpA2, w hose genes are arranged in tandem on the chromosome. Northern blot analysis indicated that momp and ompA2 are transcribed independently, Sequences of the momp open reading frame (ORF) lacking the transcriptional start site we re amplified by PCR, and an Ohm-Km2 cassette was ligated into the ORF. A pl asmid containing this construction was electroporated into H. ducreyi 35000 HP, and an isogenic MOMP-deficient mutant (35000HP-SMS2) was generated by a llele exchange. In Southern blotting, 35009HP-SMS2 contained one copy of th e Ohm-Km2 cassette in momp. 35000HP and 35000HP-SMS2 had similar outer memb rane protein (OMP) and lipooligosaccharide profiles and growth rates except for up-regulation of a putative porin protein in the mutant. Five subjects were inoculated with three doses of live 35000HP-SMS2 on one arm and two d oses of live 35000HP and one dose of a heat-killed control on the other arm in a double-blind escalating dose-response trial. Pustules developed at 7 of 10 sites inoculated with 35000HP and at 6 of 15 sites inoculated with 35 000HP-SMS2 (P = 0.14). 35000HP and 35000HP-SMS2 were recovered at similar r ates from daily surface cultures and semiquantitative cultures. The data su ggest that expression of MOMP is not required for pustule formation by H. d ucreyi in the human model of infection.