NTHi strains with rPBP3 variants are classified into three main groups (Table 1), based on the substitution of two key amino acids occurring near the KTG-motif: R517H (clustered as group I) or N526K (group II). It has also been shown that loss of repression of the AcrAB efflux pump in combination with rPBP3 may lead to a further increase in resistance. In parallel to the previously well-described PBP3-substitutions R517H and N526K, we demonstrate that Y528H confers reduced aminopenicillin susceptibility.Īntimicrobial resistance of the respiratory tract pathogen non-typeable Haemophilus influenzae (NTHi) to β-lactam antibiotics is conferred either by the production of transferrable β-lactamases or by amino acid substitutions in penicillin binding protein 3 (rPBP3), caused by point mutations of the ftsI gene. None of the isolates had frame shift insertions in the acrR gene regulating the AcrAB efflux pump.
However, the mutant remained susceptible to aminopenicillins according to EUCAST clinical breakpoints (assuming intravenous treatment) and the introduction of Y528H alone did not increase the resistance to the same level as NTHi93–57485. MICs for aminopenicillins were increased in the mutant compared to the wild-type. Introduction of the Y528H substitution in NTHi3655 resulted in positive screening for β-lactam resistance. Disc diffusion screening and broth microdilution determination of MICs for β-lactam agents were done with the NTHi3655-PBP3 Y528H mutant and were compared with the NTHi3655 wild-type as well as the original clinical isolate NTHi93–57485. influenzae (NTHi3655) was performed to introduce the Y528H substitution into wild-type ftsI (encoding for PBP3). Site-directed mutagenesis of a β-lactam susceptible H. The significance of an alternative amino acid substitution (Y528H) in this isolate was examined.
We analyzed a blood isolate, NTHi93–57485, that was categorized as aminopenicillin resistant but lacked key amino acid substitutions in PBP3 that have previously been associated with reduced aminopenicillin susceptibility. Identification and characterization of non-typeable Haemophilus influenzae (NTHi) with reduced susceptibility to β-lactam antibiotics due to mutations in penicillin binding protein 3 (PBP3) is a clinical challenge.
0 kommentar(er)
