Abstract
Purpose :
In ocular infections, despite the administration of appropriate antibiotics at MIC values according to culture results, the infections may worsen.This may be related with the route of administration that may deliver sub-MIC values of antibiotics to the infection site. In this study, our purpose was to analyse the in vitro effects of sub-MIC values of vancomycin, linezolid and imipenem on Staphylococcus spp. isolated from ocular surface and above-MIC values of them on preformed biofilms.
Methods :
Twenty-six isolates of methicillin resistant, vancomycin sensitive icaA and icaD positive Staphylococcus spp (11 S. epidermidis, 5 S. lugdunensis, 5 S. warneri, 2 S. saprophyticus, 1 S. hominis, 2 S. aureus strains) were evaluated for biofilm formation. At first stage, biofilm formation was measured spectrophotometrically after addition of vancomycin sub-MIC values (12μg/ml) to 195μl tryptose soy broth (TSB) simultaneous with 5μl bacteria (106 cfu/ml) .Then they were incubated at 37Co for 24 hours. The procedure was also repeated for linezolid (6μg/ml) and imipenem (12μg/ml). The second stage involved the addition of the antibiotics above MIC values ( 40 µg/ml vancomycin and imipenem, 8 µg/ml linazolid) on preformed biofims. After incubation at 37Co for 24 hours, spectrophotometric measurments were done at 570 nm wavelength.
Results :
With sub-MIC values, spectrophotometry detected biofilm formation with vancomycin and linezolid. With imipenem for sub- MIC values, no biofilm formation was detected. When these antibiotics were added on preformed biofilms at first stage above MIC values, optical density values were lower with imipenem than with vancomycin or linezolid.
Conclusions :
At sub-MIC values, tested antibiotics may trigger biofilm formation except imipenem. Imipenem may be more effective than vancomycin and linezolid on preformed biofilm.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.