Interspecies transfer of the penicillin-binding protein 3-encoding gene ftsI between Haemophilus influenzae and Haemophilus haemolyticus can confer reduced susceptibility to β-lactam antimicrobial agents

Mutations in <i>ftsI</i>, encoding penicillin-binding protein 3, can cause decreased β-lactam susceptibility in <i>Haemophilus influenzae</i>. Sequencing of <i>ftsI</i> from clinical strains has indicated interspecies recombination of <i>ftsI</i> between <i>H. influenzae</i> and <i>Haemophilus haemolyticus</i>. This study documented apparently unrestricted homologous recombination of <i>ftsI</i> between <i>H. influenzae</i> and <i>H. haemolyticus in vitro</i>. Transfer of <i>ftsI</i> from resistant isolates conferred similar but not identical increases in the MICs of susceptible strains of <i>H. influenzae</i> and <i>H. haemolyticus</i>.