The acrAB homolog of Haemophilus influenzae codes for a functional multidrug efflux pump

Abstract

Disruption of gene HI0894 or HI0895 in Haemophilus influenzaeRd, homologs of Escherichia coli acrAB multidrug efflux genes, caused hypersusceptibility to erythromycin, rifampin, novobiocin, and dyes such as ethidium bromide and crystal violet and increased accumulation of radioactive erythromycin, showing that these genes are expressed and contribute to the baseline level resistance of this organism through active drug efflux. The gene disruption did not produce detectable changes in susceptibility to several other antibiotics, possibly because rapid influx of small antibiotic molecules through the large H. influenzae porin channels counterbalances their efflux.Haemophilus influenzae is a well-known pathogen that colonizes the upper respiratory tract and invades the respiratory mucous membranes. H. influenzae strains frequently exhibit multiple antibiotic resistance, usually attributed to the presence of large R plasmids containing several resistance genes, each directed toward a specific antibiotic (23). However, a more general mechanism for baseline and increased levels of resistance, such as that conferred by the synergistic interaction of the outer membrane barrier and the multidrug efflux pumps (19), should also be considered.H. influenzae has only one porin, Omp2, which produces large, highly permeable channels. The large size of the channel is evident from the observations that it allowed the penetration of a 1,845-Da oligosaccharide (25) (in contrast to Escherichia coli porins, which were impermeable to 666-Da stachyose [17]) and that the intact cells showed outer membrane permeability for ␤-lactams that was much higher than that observed in E. coli (3,22). Planar lipid membrane experiments gave a singlechannel conductance of 1.1 nS in 1 M KCl (24), and the apparently low level of this conductance, in comparison with the 2.0-nS conductance obtained in the same study with E. coli OmpF porin, was a puzzle. However, it has since become clear that the 1.2-to 2.0-nS "single-channel" conductance of E. coli porin is caused by the insertion of three channels of porin trimer (18). (Furthermore, a more recent study showed that the single-channel conductance steps of H. influenzae porin had a population centered at 2.3 nS [2], although this could have resulted from the insertion of oligomers.) Thus, all assays, including the planar lipid bilayer assay, show that the H. influenzae Omp2 porin produces a much wider channel than those of E. coli porins.

Defining Genetic Fitness Determinants and Creating Genomic Resources for an Oral Pathogen

“…S7A). These mutants were disrupted for the genes encoding AcrA and AcrB, subunits of a multidrug efflux system shown in many bacteria to mediate antibiotic resistance (53,54).…”

Tetracyclines in veterinary medicine and bacterial resistance to them

“…the MtrCDE system in Neisseria gonogrhoeae (Hagman et al, 1995), or a multidrug efflux system in Haemophilus influenzae (Sanchez et al, 1997).…”

Levofloxacin Treatment Failure inHaemophilus influenzaePneumonia

“…Quality control strains used were H. influenzae ATCC 49247, H. influenzae ATCC 51907, and Escherichia coli ATCC 25922. Determination of an eventual active efflux mechanism of fluoroquinolone resistance was carried out by MIC determination in the presence and absence of carbonyl cyanide 3-chlorophenyl (CCCP) and reserpine in all three clinical strains (9).…”