Colistin-resistant Pseudomonas aeruginosa clinical strains with defective biofilm formation.

Aim: Colistin is the only effective antibiotic in some cases of Pseudomonas aeruginosa resistance to all tested antibiotics, even carbapenem. On the other hand, biofilm formation is one of the antibiotic resistance mechanisms in this bacterium. The aim of this study was to examine biofilm formation in colistin-resistant P. aeruginosa for the first time. Method: Two groups of P. aeruginosa were included in this study: 1) colistin-resistant and 2) colistin-susceptible. Biofilm formation was determined in these groups using the micro-tube test well as PCR to detect the genes involved in biofilm formation (ppk and molA). The plasmids for colistin resistance, mcr-1 and mcr-2, were also determined. P. aeruginosa ATCC 27853 was used as a control for all tests. Results: Strong biofilm formation was observed only in colistin-susceptible strains, and ppk and modA were not detected in colistin-resistant strains. The control strain P. aeruginosa ATCC 27853 possesses ppk and modA and is categorized as a strong biofilm formation group. According to the results of this study, colistin resistance is associated with defective biofilm formation, as reported by other studies on Acinetobacter baumannii.