Abstract
The ability to produce slime layer by Methicillin-resistant S. aureus (MRSA) and Methicillin-Resistant Coagulase-Negative Staphylococci (MR-CONS) isolates was investigated and the results showed that all isolates of both MRSA and MR-CONS were produced slime layer when tested by tube method but the amounts of adherent materials were different among the isolates. However, the results by Congo red agar method showed that 60% of MRSA isolates produced strong slime layer and 40% of MRSA obtained negative result, and in the case of MR-CONS all tested isolates (100%) had the ability to produce strong slime layer by this method. Similarly the ability of MRSA and Methicillin-Resistant Staphylococcus epidermidis (MRSE) isolates to produce biofilm by tissue culture plate (TCP) was investigated and the results indicated that both MRSA and MRSE showed highly and strong biofilm formation, and the OD value of biofilm formation ranged between 0.520 - 0.738, and the OD value obtained from MRSE isolates were higher compared to the MRSA isolates. Additionally the OD value of biofilm formation significantly increased in addition of 1% glucose to the media. The results showed that there are a possible correlation between Methicillin susceptibility and the biofilm formation in S. aureus isolates. The effect of Subinhibitory Antibiotics Concentration (sub-MIC) of two antibiotics (Vancomycin and Clindamycin) on the biofilm formation by MRSA and MRSE isolates were investigated and the results showed that both antibiotics at two subinhibitory concentration (one-half and two-half the MIC) were significantly inhibitory to biofilm formation by both isolates when using of each antibiotic alone, but Vancomycin was most effective than Clindamycin. Additionally, the results showed that the combination of these two antibiotics at different sub-MIC were significantly reduced or inhibited the biofilm formation by both isolates. In comparison between the using of each antibiotics alone or in combination the results showed that in the case of MRSE isolate there was no significant difference between the two treatment methods, while in the MRSA isolate there was a significant difference between the two methods. The using of each antibiotic alone (Vancomycin or Clindamycin) was most effective than the using of combination of these two antibiotics in the inhibition of biofilm formation.

Key words: Microbial biofilm, MRSA, MRSE, antibiotics