Examination of the Production of Biofilm and Acyl Homoserine Lactone (AHL) in Pseudomonas aeruginosa Isolates Exposed to Sub-inhibitory Antibiotics Concentrations

It is possible to be exposed to sub-inhibitory antibiotics concentrations due to either patients or physicians during antibiotic therapy. In this study, we aimed to examine the production of biofilm and acyl homoserine lactone (AHL) in Pseudomonas aeruginosa isolates which were exposed to sub-inhibitory antibiotics concentrations.

In this study, The bacteria incubated in Muller Hinton agar in the oven and placed antibiotic discs onto them. As the distance increases from the antibiotic discs, the effective concentration of antibiotic decreases. Furthermore, the zone without bacterial growth ends from the place where the effect of antibiotic decreases to sub-inhibitory concentration and bacterial growth starts.A model by accepting this zone in which the bacteria are exposed to the sub-inhibitory antibiotic concentration have established. The four different Pseudomonas aeruginosa isolates were exposed to sub-inhibitory concentrations of amikacin, gentamicin, imipenem, meropenem, ciprofloxacin, cefepime, ceftazidime and colistin antibiotics for 5 days. Biofilm productions of isolates pre and post exposures the antibiotic were determined using microtitration plaque. Furthermore, the cross-feeding assay was performed for AHL detection.

Biofilm production was observed in all isolates exposed to 3 isolates ceftazidime when exposed to cefepime, in 3 isolates when exposed to ciprofloxacin, in 2 isolates when exposed to colistin, in 2 isolates when exposed to amikacin, in 2 isolates when exposed to gentamicin, in 1 isolate when exposed to imipenem, and in 1 isolate when exposed to meropenem. Some of these antibiotics affected the AHL production, whereas some others deteriorated the AHL production. It was observed that all of the sub-inhibitory antibiotic concentrations led to biofilm production. Some of them increased the biofilm production in all 4 isolates, whereas some others increased the biofilm production in at least 1 isolate. The most effective group in biofilm production was the cephalosporin group and less biofilm production was observed with the carbapenems (imipenem, meropenem).

We detected that biofilm production continued in strains in which there was no AHL production or the AHL production was deteriorated. This study found, that there was no relationship between the AHL production of strains and the biofilm production.