blaROB-1 presence on pB1000 in Haemophilus influenzae is widespread, and variable cefaclor resistance is associated with altered penicillin-binding proteins

Plasmid pB1000 is a small replicon recently identified as bearing blaROB-1 in animal and human Pasteurellaceae in Spain. We identified pB1000 in 11 blaROB-1-positive Australian and North American Haemophilus influenzae isolates, suggesting a wider role for pB1000 in disseminating blaROB-1. Native H. influenzae conjugative elements can mobilize plasmids similar to pB1000 at a low frequency of 10−8, and this might account for the infrequency of blaROB-1 compared to the rate of occurrence of blaTEM-1. Altered penicillin-binding protein 3 was associated with an increased cefaclor MIC in 3 isolates.