Comparison between ica operon expression and biofilm formation in methicillin-resistant staphylococcus aureus isolated from central venous catheters under different environmental conditions

ABSTRACT

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. 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. 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. 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. 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-Nacetylglucosamine [PIA/PNAG] may not be required for biofilm development in MRSA