Antibiotic Effect on Planktonic and Biofilm-Producing Staphylococci

The pathogenic effect of Staphylococci is due to extra-cellular factors and properties such as adherence and biofilm production. The nature of the biofilm and the physiological properties of biofilm-producing bacteria result in an inherent antibiotic resistance and require further investigation. Two hundred and sixty Staphylococcal strains were cultured from 600 clinical specimens obtained from hospitalized patients. Among these, 155 were identified as coagulase-positive (CPS) and 105 as coagulase-negative (CNS) staphylococci. Staphylococcal strains were tested for biofilm production using the tissue culture plate (TCP) method. TCP detection showed that of the 155 CPS, 124 (80%) were biofilm producers, while 63 (60%) of the 105 CNS were biofilm producers. Biofilm-producing strains were scanned by scanning electron microscope (SEM) to confirm biofilm formation, study biofilm production, and examine antibiotic effects on biofilm formation. Disc diffusion method was used to study resistance of planktonic and biofilm-forming cells to antibiotics. Planktonic cells were less resistant to antibiotics than biofilm-forming cells. Microbroth dilution method and a new BioTimer assay were used to determine antibiotic MICs affecting planktonic and biofilm cells. Both methods showed that the MICs for planktonic cells were less than that for biofilm cells. The BioTimer assay was therefore found to be sensitive, accurate, and reliable, with results in agreement with those from the broth dilution method and SEM.