Diversity of ampicillin-resistance genes in Haemophilus influenzae in Japan and the United States.

Clinical isolates of Haemophilus influenzae from Japan (n = 296) and the United States (n = 100) were tested by the microdilution method for susceptibility in vitro to 10 beta-lactam antibiotics and molecular mechanisms of beta-lactam resistance. For all isolates, PCR was used to identify six elements, including beta-lactamase-producing ampicillin (AMP)-resistance (BLPAR) and beta-lactamase-nonproducing AMP-resistance (BLNAR) genes as follows: (1) TEM-1 type beta-lactamase gene, (2) ROB-1 type beta-lactamase gene, (3) part of normal ftsI gene encoding PBP3, which is involved in septal peptidoglycan synthesis, (4) a portion of the ftsI gene possessing some amino acid substitutions commonly detected in BLNAR strains, (5) p6 gene encoding P6 membrane proteins specific to H. influenzae, and (6) serotype b capsule gene.