Molecular characterisation of a meropenem-resistant Haemophilus influenzae

Background: Haemophilus influenzae β-lactam resistance is mediated by production of β-lactamase and mutations in penicillin-binding protein 3 (PBP3, encoded ftsI). Only one the 646 patient-unique H. isolated our laboratory between 2012–July 2022 was meropenem (amoxicillin, co-amoxiclav ceftriaxone) resistant. Methods: Identification susceptibility this meropenem-resistant (MRHI) confirmed disk diffusion E-test (bioMérieux) (CLSI M100). WGS performed on GridION (Nanopore) reference mapped with Geneious Prime 2022.2. PCR Sanger sequencing used to confirm results WGS. Results: The MRHI isolate negative non-typeable. ftsI subgroup IIc1 were present, signifying previously described low level PBP3 alterations that should not solely account for carbapenem resistance. Group VII2 acrR (repressor AcrAB efflux pump) substitutions observed but without reported associated frameshift mutation. There also multiple insertions ompP2 (outer membrane P2) porin, resistance.2 100% concordance Nanopore increases confidence application technology future investigations. Conclusion: Meropenem likely multifactorial, decreased influx as contributing factors. References 1. Dabernat H, et al. Diversity resistance-conferring amino acid influenzae. Antimicrob Agents Chemother 2002; 46: 2208–2218. 2. Cherkaoui A, Imipenem heteroresistance nontypeable linked a combination altered PBP3, slow drug direct regulation. Clin Microbiol Infect 2017; 118: e9–118.e19