Slime forming staphylococcus epidermidis isolated from orthopedic prosthesis infections and its sensitivity to antibiotics

ABSTRACT

Staphylococcus epidermidis [S.epidermidis] is a frequent cause of infections of indwelling medical devices especially those with orthopedic implants. S.epidermidis grows on medical devices as an adherent biofilm consisting of cells enmeshed in a sticky, extracelluar slime that is firmly attached to the underlying surface. The slim matrix makes S.epidermidis biofilm highly resistant to antibiotics and host defenses and nearly impossible to eradicate. The aim of the study is to determine importance of slime formation in S. epidermidis orthopedic prosthesis infections and to investigate if slime formation has an effect on its antibiotics sensitivity. 80 coagulase negative staphylococcus strains [CoNS] were isolated from 200 tissue specimens of patients with orthopedic prothesis infections. Out of these 80 CoNS, 52 [65%] strains were S.epidermidis. Isolated S. epidermidis were plated on Congo red agar and subjected to PCR to detect icaA and icaD genes to identify and confirm slime producing strains respectively. All biofilm producing strains were subjected to MIC and MBEC using Calgary Biofilm Device[CBD]. 36 [69%] S. epidermidis strains were slime [biofilm] producers and 16 [31%]strains were non slime [non biofilm] producers by CRA, while by PCR 39[75%] strains of S. epidermidis were biofilm producers and 13 [25%] strains were non biofilm producers. The results also revealed that the minimal biofilm eradication concentrations [MBECs] were higher than the corresponding conventionally determined MICs for all antibiotics tested. MIC 50 and MBEC 50 for vancomycin, were 2 micro g/ml versus 8 micro g/ml, gentamycin, 1 micro g/ml versus 32 micro g/ml, oxacillin, 4 micro g/ml versus 16 micro g/ml, erythromycin, 8 micro g/ml versus 64 micro g/ml, ciprofloxacin, 0.5 micro g/ml versus 2 micro g/ml and cephalothin 4 micro g/ml versus 16 micro g/ml. MIC90 and MBEC90 for vancomycin were 4 micro g/ml versus16 micro g/ml, gentamycin, 16 micro g/ml versus 128 micro g/ml, oxacillin, 8 micro g/ml versus 128 micro g/ml, erythromycin, 16 micro g/ml versus 128 micro g/ml, ciprofloxacin, 4 micro g/ml versus 8 micro g/ml and cephalothin 32 micro g/ml and 128 micro g/ml. The results of the present study confirm that ica genes can be considered a virulence marker in the pathogenesis of implant associated orthopedic infection by S. epidermidis. This study also demonstrates marked differences between the results of susceptibility testing performed according to standard NCCLS guidelines and testing based on biofilm susceptibility testing