Effects of Exogenous N-Acyl-Homoserine Lactones on Biofilm Formation and Motility in Acinetobacter nosocomialis

One of the major factors contributing to drug resistance in Acinetobacter nosocomialis infections is biofilm development, which is facilitate by quorum-sensing (QS) systems. Quorum sensing by the LuxI and LuxR homologues, AnoI and AnoR, in A. nosocomialis plays a role in biofilm formation and motility of this pathogenic bacterium. The aim of this study was to evaluate the effects of exogenous N-acyl-homoserine lactones (AHLs) on the regulation of biofilm and motility of A. nosocomialis and anoI-deletion mutant. We found that anoR mRNA expression levels in the anoI-deletion mutant were increased in the presence of different types of AHLs compared with that in the absence of exogenous AHL. Among AHLs, C12-HSL appeared to exert the greatest stimulatory effect on biofilm formation and motility. Notably, the anoI-deletion mutant also exhibited significant decreases in expression of the biofilm- and motility-related genes, csuC, csuD and pilT, decreases that were attenuated by addition of exogenous AHLs. Combining the AHL C12-HSL with C6-HSL or C10-HSL exerted synergistic effects that restored the motility phenotype in the anoI-deletion mutant. Taken together, our data demonstrate that C12-HSL may act as an important signaling molecule in A. nosocomialis through regulation of biofilm formation and cell motility, potentially providing a new target for the control of A. nosocomialis infections.

RND efflux pump systems in Acinetobacter, with special emphasis on their role in quorum sensing

Acinetobacter is an important opportunistic, multidrug resistant pathogen causing majority of nosocomial infections worldwide. The multidrug resistance is attributed by a plethora of efflux pumps and the overexpression of the same mediates export of antimicrobial agents. Quorum sensing (QS) is the cell-to-cell communication system in which bacteria produces specific signaling molecules which are transported out to the surrounding environment to communicate with other bacterial cells. It has been noticed that multidrug efflux pumps like resistance-nodulation-cell division (RND) efflux pumps play an important role in QS by exporting these signaling molecules. This review discusses various RND efflux pumps and the current understanding of the interrelationship of RND efflux pumps and QS in Acinetobacter spp. Studies demonstrate that RND efflux pumps could be considered as potential targets to block QS thereby reducing pathogenesis and antibiotic resistance. The known RND efflux pump-mediated quorum quenching strategies for Acinetobacter and other bacterial strains are discussed in detail. Finally, the prospective quorum quenching strategies targeting the transcriptional regulators of RND efflux pumps to inhibit multidrug efflux pumps are addressed.

Autophagy in Mycobacterium abscessus Infection

Autophagy is a self-degradative process that removes misfolded or aggregated proteins, clears damaged organelles, as well as eliminates intracellular pathogens playing a role in innate immunity. Mycobacterium abscessus (M. abscessus) has been reported as a causative organism in nearly 80% of the rapid growing mycobacteria (RGM) pulmonary disease. The strain exhibits two different colony types: the smooth (S) one which is considered wild-type and the rough (R) one which is the mutated strain. In accordance to the colony morphology, the S and R types display varying autophagic responses in the host cells with the R type inducing elevated autophagy compared to the S type. The major difference in the autophagy could be based on the bioactive molecules exposed on the surface of the S and R types. Though autophagy has a vital role to play in the clearance of intracellular pathogens, very little is known on the autophagy induced by M. abscessus. It has been known that the intracellular pathogens employ different strategies to evade the autophagic pathway and to survive within the host cells. This review summarizes the most up-to-date findings on autophagy induced by M. abscessus morphotypes and how M. abscessus evades the autophagic machinery to divide and thrive inside the host cells. In addition, the prospects of autophagic machinery in devising new anti-infective strategies against mycobacterial infection is also been discussed.

Autophagy in Mycobacterium abscessus Infection

Autophagy is a self-degradative process that removes misfolded or aggregated proteins, clears damaged organelles, as well as eliminates intracellular pathogens playing a role in innate immunity. Mycobacterium abscessus (M. abscessus) has been reported as a causative organism in nearly 80% of the rapid growing mycobacteria (RGM) pulmonary disease. The strain exhibits two different colony types: the smooth (S) one which is considered wild-type and the rough (R) one which is the mutated strain. In accordance to the colony morphology, the S and R types display varying autophagic responses in the host cells with the R type inducing elevated autophagy compared to the S type. The major difference in the autophagy could be based on the bioactive molecules exposed on the surface of the S and R types. Though autophagy has a vital role to play in the clearance of intracellular pathogens, very little is known on the autophagy induced by M. abscessus. It has been known that the intracellular pathogens employ different strategies to evade the autophagic pathway and to survive within the host cells. This review summarizes the most up-to-date findings on autophagy induced by M. abscessus morphotypes and how M. abscessus evades the autophagic machinery to divide and thrive inside the host cells. In addition, the prospects of autophagic machinery in devising new anti-infective strategies against mycobacterial infection is also been discussed.