Substrate Specificities and Efflux Efficiencies of RND Efflux Pumps of Acinetobacter baumannii

Abstract

Antibiotic resistant causes infections that are extremely difficult to treat. A significant role in these resistance profiles is attributed to multidrug efflux pumps, especially those belonging to Resistance-Nodulation-cell Division (RND) superfamily of transporters. In this study, we analyzed functions and properties of RND efflux pumps in ATCC 17978. This strain is susceptible to antibiotics and does not contain mutations that are commonly selected upon exposure to high concentrations of antibiotics. We constructed derivatives of ATCC 17978 lacking chromosomally encoded RND pumps and complemented these strains by the plasmid-borne genes. We analyzed the substrate selectivities and efficiencies of the individual pumps in the context of native outer membranes and their hyperporinated variants. Our results show that inactivation of AdeIJK provides the strongest potentiation of antibiotic activities, whereas inactivation of AdeFGH triggers the overexpression of AdeAB. The plasmid-borne overproduction complements the hypersusceptible phenotypes of the efflux deletion mutants to the levels of the parental ATCC 17978. Only a few antibiotics strongly benefitted from the overproduction of efflux pumps and antibacterial activities of some of those depended on the synergistic interaction with the low permeability barrier of the outer membrane. Either overproduction or inactivation of efflux pumps change dramatically the lipidome of ATCC 17978. We conclude that efflux pumps of are tightly integrated into physiology of this bacterium and that clinical levels of antibiotic resistance in isolates are unlikely to be reached solely due to overproduction of RND efflux pumps. RND-type efflux pumps are important contributors in development of clinical antibiotic resistance in However, their specific roles and the extent of contribution to antibiotic resistance remain unclear. We analyzed antibacterial activities of antibiotics in strains with different permeability barriers and found that the role of active efflux in antibiotic resistance of is limited to a few select antibiotics. Our results further show that the impact of efflux pump overproduction on antibiotic susceptibility is significantly lower than the previously reported for clinical isolates. Additional mechanisms of resistance, in particular those that improve the permeability barriers of bacterial cells and act synergistically with active efflux pumps are likely involved in antibiotic resistance of clinical isolates.

Efflux pump inhibitors of clinically relevant multidrug resistant bacteria

“…Most of the vancomycin‐resistant Enterococci are E. faecium , for which MsrC, EfrAB and EfmA efflux pumps have been reported to be the most important in conferring MDR (Table ) . Overproduction of AmvA and RND efflux pumps, such as AdeABC, AdeFGH, and AdeIJK, is associated with resistance to antibiotics in Acinetobacter baumanii (Table ) . In addition, AbeM is present in many clinical isolates of A. baumannii and has been shown to increase the MICs of antibiotics .…”

“…[31][32][33] Overproduction of AmvA and RND efflux pumps, such as AdeABC, AdeFGH, and AdeIJK, is associated with resistance to antibiotics in Acinetobacter baumanii ( Table 1). [34][35][36] In addition, AbeM is present in many clinical isolates of A. baumannii and has been shown to increase the MICs of antibiotics. 37,38 Of the several RND efflux systems found in H. pylori, HefABC contributes to MDR, 13,39 while the clinical importance of three MESs was demonstrated for N. gonorrhoeae, namely MtrCDE, MacAB, and NorM, which recognize antibiotics relevant for the treatment of gonococcal infections (Table 1).…”

“…57 Moreover, an increased expression and activity of AcrAB-TolC efflux pump is associated with a substantial reduction in expression of bacterial DNA mismatch repair proteins, such as MutS, and higher spontaneous mutation frequency. 58 Hence, EPIs Enterococcus faecium [31][32][33] Tet(K) MsrC Tet(L) EfrAB EfmA Gram-negative Acinetobacter baumanii [34][35][36][37][38] Tet(A) AbeS AbeM AdeABC AceI Tet(B) AdeDE CmlA AdeFGH MdfA AdeIJK CraA AdeXYZ AmvA…”

Integrative analysis of outer membrane vesicles proteomics and whole-cell transcriptome analysis of eravacycline induced Acinetobacter baumannii strains

“…The overproduction of RND pumps, such as AdeABC, AdeFGH, and AdeIJK is a major factor contributing to the resistance in Acinetobacter [59]. The gene for AdeB/AdeJ proteins had 3-fold differential expression in both the ATCC 19606 and JU0126 strains.…”

Biofilm formation in Acinetobacter baumannii was inhibited by PAβN while it had no association with antibiotic resistance

“…PAβN has been proposed to be an RND competitive substrate (Kourtesi et al, 2013). RND-type multidrug efflux pumps are a critical contributor to antibiotic resistance in A. baumannii (Leus et al, 2018). The effects of the PAβN on biofilm formation and dispersion of A. baumannii remain unknown.…”