New bacterial survival mechanism identified in antibiotic resistance.

Antibiotics are medicines used to prevent and treat bacterial infections. Antibiotic resistance occurs when bacteria adapt in response to the use of these medicines and become immune to their mode of action, making them harder to treat. Bacteria are becoming increasingly resistant to antibiotics, with work concentrating on the mechanisms these bacteria use to adapt to the various modes of antibiotics. Now, a study from researchers at the University of Copenhagen identifies a previously unknown survival mechanism for a commonly known type of bacteria. The team states the bacteria was observed sending out warning signals to ensure other bacteria escape ‘dangers’ such as antibiotics. The opensource study is published in the Journal of Bacteriology.

Previous studies show infections with the bacterium Pseudomonas aeruginosa have become a real concern, especially in critically ill and immunocompromised patients, with P. aeruginosa implicated in infecting patients with the lung disease cystic fibrosis. Studies of P. aeruginosa revealed four quorum-sensing systems, a system used by bacteria to regulate certain phenotype expressions, which in turn, coordinate their behaviors. One of these systems, PQS (Pseudomonas quinolone signal), is involved in a signaling system controlling virulence gene expression, swarming motility, and biofilm formation. The current study shows that P. aeruginosa bacteria use the PQS to send out warning signals when attacked by antibiotics or bacteriophages to stop the swarming of healthy bacteria into dangerous areas.

The current study creates environments in Petri dishes that resemble the surface of the mucous membranes where an infection can occur, as is the case with the lungs of a person with cystic fibrosis. P. aeruginosa cells were treated with an antibiotic (gentamicin). Results show when gentamicin is spotted directly onto the agar medium, swarming is not inhibited as no warning is signal has been sent. Data findings show when a bacterial culture treated with gentamicin is spotted on the agar there is a repulsion of untreated P. aeruginosa swarms, with the swarm avoiding dangerous areas after being warned by affected conspecifics.

The lab explain this repulsion is due to the secretion of PQS into the medium from the gentamicin-treated cells, validating the point that multiple stressors result in PQS secretion to repel other cells away from the population under attack. They go on to add their findings provide important insights into the role of PQS as a multifunctional signal that can act across long distances on surfaces.

The team surmises they show that stressed P. aeruginosa microbial cells restrict swarming of healthy cells via PQS signaling. For the future, the researchers state their data may result in the development of drugs that prevent the warning signal from being sent out, restricting antibiotic-resistance.

Source: University of Copenhagen

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