KN participated in the proteomic

analysis and revised the manuscript. NGG participated in the design of the study. SY conceived and designed portions of the study, and revised the manuscript. All authors read and approved the final manuscript.”
“Background Haemophilus influenzae is a major cause of respiratory tract infections and invasive disease, with encapsulated strains of serotype b (Hib) being most virulent [1]. Nontypeable isolates (NTHi) now account for the majority of cases of invasive disease in countries where Hib conjugate vaccines have been introduced [2–4]. NTHi vaccines have a huge potential for further reducing the global burden of disease but are not yet available [1, 5]. Beta-lactams are first-line drugs for treatment of H. influenzae infections but resistance may develop due to transferable beta-lactamases (impacting penicillins only) or alterations in the transpeptidase domain of penicillin-binding PI3K inhibitor protein 3 (PBP3), encoded by the ftsI gene (impacting all beta-lactams) [6]. Traditionally, isolates with the latter resistance mechanism have been denoted beta-lactamase negative ampicillin resistant (BLNAR), whereas isolates with both mechanisms have been denoted beta-lactamase positive amoxicillin-clavulanate resistant (BLPACR). PBP3-mediated resistance is defined by the

presence of particular amino acid substitutions (Table 1): R517H or N526K near the KTG motif in low-level resistant isolates (groups I and II, respectively), Bumetanide and the additional substitution S385T near the selleck screening library SSN motif in high-level resistant isolates (group III-like, S385T + R517H; group III, S385T + N526K)

[7–10]. Table 1 Genotypes of PBP3-mediated resistance in Haemophilus influenzae Genotype designationsa PBP3 substitutionsb SSN KTG Categoryc Level Group S385 R517 N526 rPBP3 High IIId T   K     III-likee T H     Low II     K     I   H   sPBP3 NA NA       aAccording to Ubukata et al.[7], Hasegawa et al.[8], Garcia-Cobos et al.[9], Hotomi et al.[10] and this study. NA, not applicable. bEssential amino acid substitutions in PBP3 (transpeptidase domain, 338–573) with the amino acid sequence of H. influenzae Rd KW20 [GenBank:U32793] as reference. SSN, Ser-Ser-Asn motif; KTG, Lys-Thr-Gly motif. crPBP3, isolates with PBP3 sequences conferring resistance to beta-lactams (isolates assigned to groups I, II, III-like and III); sPBP3, isolates with PBP3 sequences conferring wild-type susceptibility to beta-lactams (remaining isolates). dOriginally reserved for isolates with the additional substitutions M377I and L389F by Ubukata et al.[7], modification proposed by Hotomi et al.[10]. eOriginally categorized as group I by Ubukata et al.[7], new group assignment proposed by Garcia-Cobos et al.[9]. An increased prevalence of PBP3-mediated resistance (hereafter denoted rPBP3) has been observed worldwide [2, 4, 11–16].