In vitro effects of antibiofilm agents and antibiotics on coagulase-negative staphylococci

Coagulase negative staphylococci (CoNS) are important nosocomial pathogens that cause biofilm infections. Biofilm provides advantages for microorganisms to resist antibiotics and host immune systems. Considering the increased antibiotic resistance, alternative treatments are needed to combat biofilm infections. In the present study, the effects of antibiotics including gentamicin (GEN), ciprofloxacin, doxycycline (DOX), rifampicin (RIF) and antibiofilm agents including N-acetylcysteine (NAC), ethylenediaminetetraaceticacid (EDTA), nisin (NIS), farnesol (FAR) on clinical CoNSbiofilm and IS256, icaA gene expression levels were evaluated. Forty-five CoNS strains were isolated from patients' catheters, at Manisa Celal Bayar University Hospital. The minimum inhibitory concentrations (MICs) of agents were detected by broth microdilution method with European Committee for Antimicrobial Susceptibility Testing (EUCAST) criteria. The combined effects of agents were investigated by checkerboard method. The antibiofilm effects of combinations were investigated by spectrophotometric microplate method. The effects of combinations on IS256 and icaA gene expressions were evaluated by real-time quantitative reverse-transcriptase PCR. Twenty-four isolates (53.3%) were detected as strong biofilm producer. Biofilm production was inhibited in seven isolates in the presence of EDTA+RIF and NIS+DOX while NIS+GEN combination and RIF inhibited biofilm in six isolates. Nine combinations were found to have synergistic effect against isolate #6 which are resistant to four different antibiotics. The expressions of icaA and IS256 were downregulated in the presence of EDTA, NAC+CIP, NAC+GEN, NIS+GEN, FAR+GEN. Antibiofilm agent/antimicrobial combinations could have promising effects for preventing catheter colonization. The further studies on antibiofilm treatment strategies would be beneficial for decreasing morbidity-mortality rates and healthcare costs caused by biofilms.