Use of trans-complementation method to determine the effects of various ftsI mutations on β-lactamase-negative ampicillin-resistant (BLNAR) Haemophilus influenzae strains

Abstract

Haemophilus in uenzae is causative agent of serious infections especially among children. β-lactam antibiotics are commonly used for treatment of these infections. Among H. in uenzae isolates, β-lactam resistance can be due to the presence of either a β-lactamase, or in β-lactamase negative ampicillin resistant strains (BLNAR), to mutations in the ftsI gene that generate altered PBP3 with reduced a nity for β-lactams. The role of speci c amino acid substitutions in PBP3 in producing a BLNAR phenotype has been thus far demonstrated by ftsI sequencing and deduced PBP3 amino acid substitutions of large numbers of strains with a BLNAR phenotype, by transforming susceptible recipient strains with ftsI genes from BLNAR strains, and by using site directed mutagenesis of the ftsI gene to generate desired substitutions. However, reversal of resistance in BLNAR strains by trans-complementation with wild-type ftsI has never been demonstrated and might be a useful tool in the investigation of β-lactam resistance in H. in uenzae.The aim of this study was to determine the effect of trans-complementation with wild-type ftsI on the βlactam susceptibility of H. in uenzae with various β-lactam susceptibility phenotypes and genotypes. For this purpose, wild type ftsI gene encoding for PBP3 was ampli ed in whole from β-lactam susceptible H. in uenzae Rd and cloned in pLS88 plasmid to obtain pADUTAS17, which was then used to transform known BLNAR strains, susceptible strains, and a strain (CF55) with wild type ftsI but unexplained reduced β-lactam susceptibility. Ampicillin and cefotaxime MICs were determined after transformation with pLS88 and pADUTAS17 plasmids. The results showed that antibiotic susceptibilities were not affected by transcomplementation for isolates carrying wild type ftsI gene, including strain CF55. However, transcomplementation for all BLNAR strains showed decreases between -0.957 and 0.5-fold for ampicillin and cefotaxime, con rming the role of the PBP3 substitutions in the BLNAR phenotype of these isolates.These results show that trans-complementation might be a useful tool in the investigation of decreased β-lactam susceptibility in H. in uenzae.

Haemophilus influenzae carriage and antibiotic resistance profile in Belgian infants over a three-year period (2016–2018)

“…Beta-lactamase-negative ampicillin resistant H. influenzae or BLNAR is one of the problems for the treatment of H. influenzae with beta-lactam antibiotics. Specific amino acid substitutions have been identified by sequencing of the ftsI gene, producing a BLNAR phenotype ( Yalçın et al, 2022 ). BLNARS are divided into groups I, II, III and III-like defined by the amino acid mutation patterns at specific sites ( Hotomi et al, 2007 ).…”