Finally, the high hospitalization rate of patients with ST14-PBP3 type A corresponds well with the potential of this strain to cause pneumonia [25] and invasive disease [3, 4, 42]. These observations are in accordance with a recent population study suggesting association ABT-888 chemical structure between population structure and disease [53]. In conclusion, the association between rPBP3 and pathogenicity suggested by the regression analysis most likely reflects that some of the

most frequently occurring rPBP3 strains in this study also possessed strain-associated virulence properties. Identification of virulence determinants is beyond the scope of this study. However, our observations underline AR-13324 mw that studies on the correlation between resistance genotypes and pathogenicity should include molecular strain characterization. Accordingly, the previously reported association between PBP3-mediated resistance and clinical characteristics [17, 51] may be spurious. Conclusions The prevalence of rPBP3 in H. influenzae is increasing worldwide, and high-level resistant strains are emerging in new geographic regions. In this study of eye, ear and respiratory isolates in Norway, the rPBP3 prevalence was 15%, with four strains accounting for 61% of the resistant isolates. Group II low-rPBP3 isolates predominated, and significant proportions of isolates were non-susceptible to cefotaxime and meropenem. Group III high-rPBP3 was identified for

the first time in Northern Europe. The results support a role of horizontal GSK2118436 datasheet gene transfer in the emergence of rPBP3 and Atazanavir indicate phylogeny restricted transformation. Comparative analysis with data from previous studies

indicates wide dissemination of clonally related rPBP3 strains. Notably, two strains highly prevalent in Norway (ST14 and ST367 with PBP3 type A) are common in invasive disease in Europe and Canada. Continuous monitoring of beta-lactam susceptibility is necessary to ensure safe empiric therapy in severe disease and to detect a future shift from low-level to high-level resistance. The need of a global system for molecular surveillance of rPBP3 strains is underlined. The novel approach of combining MLST and ftsI/PBP3 typing is a powerful tool for this purpose. Acknowledgements The work was supported by grants from Vestfold Hospital Trust, University of Tromsø, the Scandinavian Society for Chemotherapy (SSAC), and the Norwegian Surveillance Programme for Antimicrobial Resistance (NORM). We thank the staff at the laboratories contributing with isolates; NORM for access to the surveillance database; Raymond S. W. Tsang and Fredrik Resman for sharing data; and the following for excellent technical assistance: Astrid Lia, Anja Hannisdal and Wenche Petterson (susceptibility testing, handling of isolates etc.); Anne Gry Allum (PFGE) and Martha Langedok Bjørnstad (MLST). References 1. Jordens JZ, Slack MPE: Haemophilus influenzae : Then and now.