Evaluation of the relationship between biofilm formation and antibiotic resistance in coagulase-negative staphylococci isolated from blood cultures of intensive care unit patients.

Elucidating the relationship between biofilm formation and specific antibiotic resistance is important for understanding resistance mechanisms. In this study, the antibiotic resistance profiles of 64 coagulase-negative staphylococci (CoNS) strains isolated from intensive care patients were determined using the VITEK-2 compact system, and their biofilm production ability was assessed using the microtiter plate method to investigate the relationship between the two. Additionally, the minimum biofilm eradication concentrations (MBEC) of vancomycin, linezolid, trimethoprim/sulfamethoxazole, and ciprofloxacin were determined against isolates with varying biofilm production capacities. All the strains were susceptible to linezolid, teicoplanin, and vancomycin, while resistant to ampicillin, benzylpenicillin, and rifampicin. Resistance rates to other antibiotics ranged between 1.6% (quinupristin/dalfopristin) and 96.9% (oxacillin). Overall, 48.4% of the isolates produced biofilm. The biofilm production potential of Staphylococcus epidermidis strains (62.1%) was significantly higher than that of non-S. epidermidis CoNS strains (37.1%) (p < 0.05). No significant relationship was found between biofilm production and specific antibiotic resistance (p > 0.05). Contrary to the general literature, non-biofilm-producing strains were resistant to a greater number of antibiotics than biofilm-producing strains (p < 0.05). Crucially, MBEC values demonstrated a strong positive correlation with biofilm density, increasing up to > 1024 μg/mL in strong biofilm producers. The results indicate that biofilm production does not predict specific antibiotic resistance, and that non-biofilm-producing strains may have compensated for the lack of biofilm production by developing specific antibiotic resistance. However, biofilm formation confers significant phenotypic tolerance, necessitating much higher antibiotic concentrations for eradication than those indicated by conventional susceptibility testing. In addition to vancomycin, teicoplanin, and linezolid, daptomycin, tigecycline, trimethoprim/sulfamethoxazole, and quinupristin/dalfopristin were also found to be effective options for multidrug-resistant planktonic infections, though their efficacy against biofilm-embedded cells may be substantially limited.