Detection of Quorum Sensing Signal Molecules and Identification of an Autoinducer Synthase Gene among Biofilm Forming Clinical Isolates of Acinetobacter spp.

Abstract

BackgroundQuorum sensing is a term that describes an environmental sensing system that allows bacteria to monitor their own population density which contributes significantly to the size and development of the biofilm. Many gram negative bacteria use N-acyl-homoserine lactones as quorum sensing signal molecules. In this study, we sought to find out if the biofilm formation among clinical isolates of Acinetobacter spp. is under the control of autoinducing quorum sensing molecules.Methodology/Principal FindingsBiofilm formation among clinical isolates of Acinetobacter spp. was assessed and the production of signal molecules were detected with Chromobacterium violaceum CV026 biosensor system. Characterisation of autoinducers was carried out by mass spectrometric analysis. We have also reported the identification of an autoinducer synthase gene, abaΙ among the isolates that produce quorum sensing signal molecules and have reported that the mutation in the abaI gene influences their biofilm forming capabilities. Using a microtitre-plate assay it was shown that 60% of the 50 Acinetobacter spp. isolates significantly formed biofilms. Further detection with the biosensor strain showed that some of these isolates produced long chain signal molecules. Mass spectrometric analysis revealed that five of these isolates produced N-decanoyl homoserine lactone and two isolates produced acyl-homoserine lactone with a chain length equal to C12. The abaΙ gene was identified and a tetracycline mutant of the abaΙ gene was created and the inhibition in biofilm formation in the mutant was shown.Conclusions/SignificanceThese data are of great significance as the signal molecules aid in biofilm formation which in turn confer various properties of pathogenicity to the clinical isolates including drug resistance. The use of quorum sensing signal blockers to attenuate bacterial pathogenicity is therefore highly attractive, particularly with respect to the emergence of multi antibiotic resistant bacteria.

Predation Efficacy of <i>Bdellovibrio bacteriovorus</i> on Multidrug-Resistant Clinical Pathogens and Their Corresponding Biofilms

“…Genotypically, drug-resistant strains were screened for genes involved in biofilm formation by PCR using primers as described previously (11)(12)(13)(14)(15). The primer sequences and corresponding product length used in this study are presented in Table 1.…”

The bitter taste of infection

“…AHLs are highly conserved molecules used by many Gramnegative bacteria to coordi nate gene expression (8). Although P. aeruginosa is the beststudied AHL system and arguably the most relevant human patho gen in this group of opportunists, similar signaling systems are widespread, particu larly in the marine Vibrios and Aeromonas species, as well as in common opportunists such as Acinetobacter and Burkholderia spe cies (11,12). Thus, T2R signaling would be expected to contribute to innate immune defenses against a number of potential pathogens that are associated with respi ratory infection.…”

Iron limitation enhances acyl homoserine lactone (AHL) production and biofilm formation in clinical isolates ofAcinetobacter baumannii

“…Such communication used by the bacteria is chemical in nature and generally designated as quorum sensing (QS), small diffusible molecules produced by bacteria which can reach other cells and help to communicate. 14,15 Acyl homoserine lactones (AHLs) are major class of autoinducer signals used by Gram negative bacteria to regulate diverse physiological functions such as virulence factors and biofilm. 16 In A. baumannii, 2 major genes, LuxI and LuxR, that encodes an AbaI synthase and AbaR receptor are involved in AHL production and regulation.…”