Growth phase-dependent expression of RND efflux pump- and outer membrane porin-encoding genes in Acinetobacter baumannii ATCC 19606

Objectives: To analyse the expression of resistance-nodulation-division (RND) efflux pumps and outer membrane porins during various growth phases of Acinetobacter baumannii ATCC 19606. Methods:Expression of five different RND pump-encoding genes (adeB, adeG, adeJ, AciBau_2436 and AciBau_2746) and two outer membrane porin-encoding genes (carO and oprD) was analysed at four growth timepoints, representing early, mid and late log phases and the stationary phase using quantitative RTPCR. Results:The adeB and adeJ RND pump genes were expressed at higher levels than all of the other RND pumps, though their expression was reduced at higher cell density. The adeG gene was found to be constitutively expressed, albeit at much lower levels than those seen for adeB or adeJ. The previously uncharacterized AciBau_2436 was found to be expressed in the early exponential phase. The expression level of oprD was found to be inversely proportional to cell density, while that of carO was found to increase in the mid-log phase but then decrease in the later stages of the growth phase. Conclusions:This work shows cell density-dependent expression of adeB, adeJ, AciBau_2436, carO and oprD genes, suggesting a role of global regulatory mechanisms in the expression of these genes in A. baumannii ATCC 19606.