The Effect of Sub-Minimal Inhibitory Concentrations of Daptomycin and Linezolid on Biofilm Formation of Methicillin Resistant Isolated from Clinical Samples.

OBJECTIVES

The aim of this study was to determine the development of resistance and changes in biofilm forming abilities in methicillin-resistant (MRSA) isolates exposed to sub-minimal inhibitory concentrations (sub-MICs) of daptomycin and linezolid; and to investigate the presence of the methicillin resistance gene () and the biofilm-associated genes () by polymerase chain reaction.

MATERIALS AND METHODS

This study was carried out with thirty-two MRSA isolates. The susceptibility of the isolates to daptomycin and linezolid was investigated by the broth microdilution method, and MIC values were determined (1 MIC). After serial passages, the 2 MIC and the 3 MIC values were similarly detected. Before and after serial passages, the biofilm-forming abilities of MRSA isolates were examined using the microtiter plate (MTP) method.

RESULTS

When the daptomycin and linezolid 1 MIC and 3 MIC values of the isolates were compared, there was a 2-8 fold increase in linezolid (<0.05) and a 4-32 fold increase in daptomycin (<0.05). According to the MTP method, 20 (62.5%) of the 32 isolates formed biofilm at various levels, while 12 (37.5%) did not form biofilm. After the second series of passages, biofilm formation was observed in 19 (59.4%) isolates with daptomycin (p>0.05) and in 16 (50%) isolates with linezolid (p>0.05). The gene was found in all isolates. Also, and genes were detected in 31 (96.9%) of 32 MRSA isolates.

CONCLUSION

MRSA isolates exposed to sub-MICs of the antibiotics daptomycin and linezolid were observed to form biofilms at varying levels or to lose their ability to form biofilms. The induction, reduction or eradication of biofilm depended on the type of antibiotic and the MRSA isolate.