PCR screening for beta-lactamase-negative ampicillin-resistant strains of Haemophilus influenzae

Problems with MIC based methods and breakpoints, has prompted a move to genotypic definition and detection of B-lactamase negative ampicillin resistant (BLNAR) H. influenzae. Almost all BLNAR strains have an N526K substitution in penicillin binding protein 3 (PBP3) and single nucleotide specific (snp) PCR methods have been developed to interrogate the ftsI gene relevant to that substitution. In published methods, the design of specific reverse primers was based on the AAT (N) to AAG (K) mutation at the 1576-1578 codon seen in BLNAR strains sequenced at that time. There is relatively little published data on the evaluation of these primers, and their performance is in question as it is now recognised that in many BLNAR strains the N526K is associated with AAA. This study aims to evaluate existing and new snp PCR primers for detecting N526K BLNAR H. influenzae.