Comparative analysis of proteins, drug resistance, and biofilm formation in free-swimming bacteria and their surface-attached counterparts

In this study, Pseudomonas aeruginosa PAO1 cells were cultured to confluence, and the bactericidal activity of ceftazidime, imipenem, levofloxacin, ciprofloxacin, amikacin, gentamicin, and tobramycin against planktonic bacteria and 1-day-old, 3-day-old, and 5-day-old biofilm cells were measured. The results showed that the bactericidal activity of the above-mentioned antibiotics against 5-day-old biofilm bacteria were more than 256-, more than 256-, 32-, 16-, 64-, 128- and 128-fold lower than that against planktonic cells, respectively. The biofilm tagged with green fluorescent protein were observed with confocal laser scanning microscopy and the protein expression in biofilm bacteria of all three different ages and their planktonic counterparts were compared. The differentially expressed proteins were further identified by peptide mass fingerprinting. The results showed that the thickness of the biofilms increased from 4 mu m on the first day to 20 mu m on the fifth day. The increasing biofilm thickness and some of the identified proteins such as GDP-mannose dehydratase might partially explain the difference of the bactericidal activity of the above antibiotics against biofilm cells. Although the role of the differentially expressed proteins in biofilm drug resistance needs to be explored further, the results showed that fluoroquinolone antibiotics are the better choice for treatment of P. aeruginosa biofilm-associated infections.