Complementary Regulation of BfmRS Two-Component and AbaIR Quorum Sensing Systems to Express Virulence-Associated Genes in Acinetobacter baumannii.

Acinetobacter baumannii expresses various virulence factors to adapt to hostile environments and infect susceptible hosts. This study investigated the regulatory network of the BfmRS two-component and AbaIR quorum sensing (QS) systems in the expression of virulence-associated genes in A. baumannii ATCC 17978. The ΔbfmS mutant exhibited a significant decrease in surface motility, which presumably resulted from the low expression of pilT and A1S_0112-A1S_0119 gene cluster. The ΔbfmR mutant displayed a significant reduction in biofilm and pellicle formation due to the low expression of csu operon. The deletion of abaR did not affect the expression of bfmR or bfmS. However, the expression of abaR and abaI was upregulated in the ΔbfmR mutant. The ΔbfmR mutant also produced more autoinducers than did the wild-type strain, suggesting that BfmR negatively regulates the AbaIR QS system. The ΔbfmS mutant exhibited no autoinducer production in the bioassay system. The expression of the A1S_0112-A1S_0119 gene cluster was downregulated in the ΔabaR mutant, whereas the expression of csu operon was upregulated in this mutant with a high cell density. In conclusion, for the first time, we demonstrated that the BfmRS-AbaIR QS system axis regulated the expression of virulence-associated genes in A. baumannii. This study provides new insights into the complex network system involved in the regulation of virulence-associated genes underlying the pathogenicity of A. baumannii.

Antibacterial Activity of Hibicuslide C on Multidrug-Resistant Pseudomonas aeruginosa Isolates.

Pseudomonas aeruginosa is a gram-negative bacterium that is frequently related to natural resistance to many drugs. In this work, the inhibition of growth against P. aeruginosa and multidrug-resistant P. aeruginosa (MDRPA) isolated from patients at Kyungpook National University was confirmed for hibicuslide C, essential oil components from Abutilon theophrasti. Hibicuslide C has antifungal activity with membrane disruption and apoptotic response against Candida albicans. However, its antibacterial activity was not reported yet. Cells treated with hibicuslide C was showed that its antipseudomonal activity is related to gDNA fragmentation and damage by TUNEL and gDNA electrophoresis. Furthermore, hibicuslide C worked synergistically with fluoroquinolones and rifampicin against MDRPA regardless of the ATP-associated mechanism. The antibiofilm activity possessed sole-resulting tissue culture plate method; besides that, the antibiofilm activity of other antibiotics was supported in particular MDRPA. The essential oil components like hibicuslide C may have antipseudomonal activity and, furthermore, increase in bacterial antibiotic susceptibility.