Evaluation of the Relationship Between Microenvironment and Biofilm and Coagulase Responses of Staphylococcus aureus Strains Under the Effect of Gentamicin
The frequency of infections caused by Staphylococcus aureus strains and the rate of antibiotic resistance among these strains are gradually increasing. Accordingly, serious problems emerge in the treatment of community or hospital acquired S.aureus infections. This study was aimed to determine the role of MIC and sub-MIC concentrations of gentamicin on biofilm and coagulase forming effects of S.aureus in in vitro test systems and cell cultures. A standard S.aureus ATCC 25923 strain and two clinical S.aureus strains isolated from blood cultures (Cl and C2) were included in the study. Gentamicin MIC values of the strains were determined with microdilution method at the cation-adjusted Mueller Hinton broth according to CLSI standards. For each strain, MIC, 50% MIC and 25% MIC values of gentamicin were determined separately. At the determined MIC values, biofilm formations of strains were determined with crystal violet method spectrophotometrically. Also, coagulase activities of the strains were evaluated in glass tubes. Human origin epithelial cell cultures namely HEp-2 cell lines, were infected with the standard and clinical S.aureus strains (Multiplicity of infection: 50/1) and left for incubation for two hours. After all, MIC, 50% MIC and 25% MIC values of gentamicin, were added to infected cell lines and incubated for 18 hours. Cells were blown up with distilled water and then bacteria were collected. Biofilm formation and coagulase production of these bacteria were evaluated. When S.aureus ATCC 25923 strain and Cl strains' biofilm formation was evaluated before (in vitro) and after incubation in cell culture, no difference was observed. However in C2 strain, under the effect of MIC level gentamicin, biofilm formation was occurred after interaction with the cell. In the same way, when coagulase responses were evaluated, after interaction with the cell, coagulase production of C2 strain was inhibited. These results indicated that, phenotypic characteristics such as biofilm formation and coagulase production might change during the process of bacterial adaptation to microenvironment. Further advanced experimental modelling designed with different combinations of antibiotics and different cell lines may provide data about the causes and timing of these phenotypic changes and shed light on the development of new treatment policies
