Longitudinal European surveillance study of antibiotic resistance of Haemophilus influenzae

We assessed the current resistance rates of Haemophilus influenzae against beta-lactams and other agents in Europe and compared the results with those of our previously performed surveillance study.

MICs of the antibiotics were determined using broth microdilution. The penicillin-binding domain of PBP3 of beta-lactamase (BL)-negative, amoxicillin-resistant (BLNAR) isolates was sequenced.

The percentage of BL-positive and BLNAR strains ranged from 0% to 17.6% and 0% to 33.9%, respectively. Compared with 1997/98 and 2002/03, the overall percentage of strains non-susceptible to amoxicillin decreased from 19.8% and 23.3%, respectively, to 16.4% in 2004/05. The percentage of BL-producing strains decreased from 11.0% and 13.7%, respectively, to 7.6%, whereas the number of BLNAR strains remained stable (8.8% and 9.6%, respectively, versus 8.8% in 2004/05). Comparison of penicillin binding protein (PBP) 3B gene sequences between BLNAR and susceptible strains revealed novel amino acid mutations.

In spite of large inter-regional differences, the overall resistance of H. influenzae to amoxicillin in Europe seems to decline due to a decreasing number of BL-producing strains, whereas the overall percentage of BLNAR strains seems relatively constant.