Comparison of different methods for detection of biofilm formation in staphylococcus aureus and epidermidis isolates from central venous catheter

Background: The predominant species isolated on indwelling medical devices are Staphylococcus aureus &epidermidis (Staph. aureus & epidermidis). Biofilm formation ability is recognized as an important virulence factor in both of them. Objective: this study was conducted to compare three different methods for detection of biofilm formation ability (virulence factor) in Staph. aureus & epidermidis isolated from central venous catheter (CVC). Methods: Staph. aureus and epidermidis strains were isolated from trypticase soya broth (TSB) of CVC from 156 pateints . Two phenotypic methods were used for detection of biofilm production; qualitative Congo red agar (CRA) and quantitative Microtiter plate (MTP). PCR ( genotypic method) was used to determine the presence of icaA/D gene. Results: A total of 50 staphylococcal (32 Staph. aureus and 18 epidermidis) strains isolated and identified from 156 pateints with infected CVC. Biofilm production was detected in 25(50%) isolates by CRA and 26 (52%) by MTP method (36% strong, 16% intermediate ) .The icaA/D gene was detected in 28(56%) staphylococcal isolates. the ability of Staph. epidermidis for biofilm formation was(61.1%) which was higher than Staph. aureus strains (53.1%) but with no significant difference(p<0.4).There was excellent agreement between PCR &CRA methods (Kappa value of 0.72, P< 0.001) , also between PCR& MTP (Kappa value of 0.796, P<0.001).Conclusion: Staphylococci isolated from CVC showed high rate of biofilm production. All slime producing staphylococci were positive for ica A /D genes indicating the important role of ica genes as virulence marker in staphylococci biofilm. CRA is qualitative, Simple, inexpensive and easily reproducible method and convenient as screening method. MTP is semi quantitative method reflects the severity of the condition and so may help in the determination of suitable line of management and remain a precious tool for in vitro screening.