Comparison between Ica Operon Expression and Biofilm Formation in Methicillin-Resistant Staphylococcus Aureus Isolated from Central Venous Catheters under Different Environmental Conditions

Abstract

Background: Methicillin-resistant Staphylococcus aureus (MRSA) infections are complicated by the ability of the organism to grow in surface-adhered biofilms on a multitude of inert synthetic surfaces including those involving indwelling medical devices. Intensive care unit (ICU) patients using central venous catheters (CVCs) are particularly at risk of acquiring device-related infections, which involve biofilms. Objectives: This study was carried out to compare intercellular adhesion (ica) operon expression and biofilm formation in MRSA isolated from CVCs grown under different environmental conditions. Methodology: Seven hundred sixteen central venous catheters tips were tested for MRSA colonization. Semiquantitative measurements of biofilm formation were determined for all MRSA isolates grown under different environmental conditions: Brain heart infusion (BHI) medium, BHI supplemented with 4% sodium chloride (NaCl) and BHI supplemented with 1% glucose (Glu). The ica operon expression were compared in all MRSA isolates grown under different environmental conditions using RT-PCR. Results: The overall catheter tip colonization rate was 36.87%. Staphylococci were isolated from 56.06%. The distribution of the isolated Staphylococci was as follow: Staphylococcus epidermidis (S. epidermidis) 34.8%, Staphylococcus aureus (S. aureus) 12.12% and other Coagulase negative Staphylococci CoNS 9.09%. Out of 32 S.aureus isolates 9 were MRSA (28.125%). Under standard laboratory conditions in BHI medium 22.22% of MRSA isolates were capable of biofilm development. This number increases to 77.77% when grown in BHI supplemented with 1% glucose. In contrast, growth in BHI supplemented with 4% NaCl induces biofilm in 11.11%. Among the 9 MRSA isolates, growth in the presence of NaCl resulted in activation of ica transcription in 8 strains but failed to induce substantial biofilm development in any of these isolates [weak -but measurable- biofilm formation was detected in medium supplemented with NaCl by one strain]. Glucose-mediated induction of biofilm formation in the 9 MRSA isolates correlated with weakly to moderately increased ica operon expression in 6 isolates. Interestingly, ica operon transcription was more potently activated by NaCl than by glucose in all of the MRSA isolates examined except one strain. Conclusion: There appears to be little correlation between ica operon regulation and biofilm formation in MRSA, suggesting that the ica operon and polysaccharide intercellular adhesin, or poly-N- acetylglucosamine (PIA/PNAG) may not be required. for biofilm development in MRSA