1-(1-naphthylmethyl)-piperazine Inhibition assay successfully rules out efflux pump overexpression in Acinetobacter baumannii.

BACKGROUND

Antimicrobial resistance (AMR) in Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. (ESKAPE pathogens), notably in carbapenem-resistant Acinetobacter baumannii, is a pressing global health concern, contributing to significant AMR-associated mortality. Efflux pump overexpression plays a crucial role in the multidrug resistance (MDR) of A. baumannii, but the identification of efflux-overexpressing strains remains challenging.

METHODS AND RESULTS

We evaluated the performance of an efflux pump inhibition assay in comparison with RT-qPCR, to assess efflux pump overexpression in a collection of clinical A. baumannii strains. Sixty MDR strains and a wild one were analyzed. The inhibition assay was positive for 34 and negative for 27 strains, respectively. Results were in agreement with RT-qPCR in 67.2% of the tested strains (39/58). Cohen's kappa showed a fair agreement between inhibition assay and RT-qPCR (Cohen's kappa = 0.37). Inhibition by 1-(1-NaphthylMethyl)-Piperazine (NMP), but not by Phenylalanine-Arginine-β-Naphthylamide (PaβN), was in moderate agreement with RT-qPCR (Cohen's kappa = 0.41). Furthermore, gpi alleles were associated with efflux pump overexpression (p = 0.03), suggesting potential links between genetic diversity and efflux pump overexpression. RT-qPCR showed a significant efflux pump overexpression for 4 (16.7%) out of 24 inhibition assay negative strains.

CONCLUSIONS

Our findings support the ability to reliably rule out efflux pump overexpression in A. baumannii strains displaying a negative result with an inhibition test relying on NMP. However, confirmatory analyses are necessary for strains that test positive.