Quorum sensing in Acinetobacter sp.

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

Quorum sensing allows bacteria to communicate and monitor their own population density, having this ability enables them to monitor and decide on the correct size of biofilm to produce depending on the environment and the general function the biofilm will undertake. It has been seen that numerous gram-negative bacteria use N-acyl homoserine lactones as sensing molecules. This study looked at a particular gram negative aerobic coccobacilli, Acinetobacter to see whether it too used quorum sensing molecules.

This type of bacteria is under investigation here as they are commonly observed in the hospital environment and are known to cause numerous nosocomial infections. Some common infections they have been isolated from and seen to cause are, septicemia, pneumonia and urinary and wound infections.

The method undertaken here was that fifty isolates of the Acinetobacter spp. were isolated and were monitored using a Chromobacterium violaceum CV026 biosensor monitor system. Mass spectrometry was also used to observe whether AHL’s were produced by any of these isolates. They also incubated some of the isolates to see if this inhibited or increased biofilm formation.

The results saw that 60% of the isolates formed significant biofilms after a prolonged period of incubation and that time incubated appears to have a significant effect as those incubated for 48 hours had much larger biofilms compared to those at 24 hour periods. The incubation test, also known as the microtiter plate method was repeated three times and so the results were validated and replicated thus increasing the strength of the conclusions made. Regarding the AHL production, this was not as significant, all of the 50 isolates produced colourless colonies in the CV026 induction test and this means that none of the isolates here produce short chain AHL’s however seven of the isolates did produce long chain AHL’s. 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.

Due to the small number of isolates producing AHL’s the authors then decided to look and try and identify whether a specific gene was present in the seven isolates to determine the producer of AHLs within. 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, so it appears that this gene causes the communication to occur and without it the biofilm formation is very much hindered, if not completely inhibited.

The conclusions made from this study therefore state that these signal molecules are of great significance in biofilm formation and therefore show possible ways to alter these isolates so as to not use this gene therefore reducing biofilm formation and aiding in pathogenic resistance, thus increasing the health and such of hospitals and medical facilities, anywhere that has been affected by these isolates.

Therefore this is extremely useful in today’s life and will provide immeasurable steps forward in increasing the cleanliness of many areas, and hopefully reducing disease and infections because of this species.

 

The paper is available at:

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0036696

 

Reference:

Anbazhagan D, Mansor M, Yan GOS, Md Yusof MY, Hassan H, et al. (2012) Detection of Quorum Sensing Signal Molecules and Identification of an Autoinducer Synthase Gene among Biofilm Forming Clinical Isolates of Acinetobacter spp. PLoS ONE 7(7): e36696. doi:10.1371/journal.pone.0036696