Investigation of biofilm related antibiotic susceptibilities of bacteria frequently isolated from catheter related hospitalinfections

Local and systemic infection risks are one of the most important complications of catheters used for diagnosis and treatment in hospitalization process. This study is undertaken on the basis of the biofilm formation by microorganisms oncatheter surface is one of the important factors which increase the resistance and complicate the treatment process. In this study, the sensitivity of methicillin resistant S.aureus (MRSA), methicillin resistant coagulase negative staphylococcus (MR-CNS) and P.aeruginosaisolates from the catheters of inpatients hospitilized in different clinics and intensive care units in Başkent University Medicine Faculty Hospital between 2006-2009 was investigated in vitro in planctonic phase and on sessile cells after biofilm was formed. Vancomycin, ciprofloxacin, rifampicin, gentamicin, meropenem, tigecycline, linezolid, cephtazidime and cephazolin were preferred for MRSA and MR-CNS isolates and ciprofloxacin, gentamicin, meropenem, tigecycline, piperacillin, ceftazidime and amikacin were selected for P.aeruginosa. First of all, the sensitivity of planktonic cells to antibiotics was examined so minimal inhibitor concentrations (MIC) and minimal bactericidal concentrations (MBC) were determined. Next, each strain was transformed to sessile cell in biofilm environment, and MIC and MBC values were determined for sessile cells. Double and triple antibiotics combinations were arranged, the effectiveness of combinations were studied on both planktonic and biofilm cells with multiple-combination bactericidal testing (MCBT) method. The data set obtained from planktonic and biofilm cells with each antibiotic analyzed with two proportion z test. In conclusion, a significant decreases were found in the sensitivities of sessile cells when compared to planktonic cells. Experiments with both double and triple antibiotic combinations showed a significant decrease in the sensitivities of sessile cells to all combinations tested. In the comparison of effectiveness of double and triple combinations against planktonic and sessile cells in terms of the inhibition of more than %90 of the strains, no difference was determined.