B-238. Biofilm Formation by Invasive Streptococcus pyogenes Strains
Single-species and multispecies biofilms are considered the most abundant ubiquitous life form among microorganisms including streptococci. Recently, has been demonstrated that GAS strains recovered from patients with treatment failure in fact form biofilms in vitro with variable efficiency and that, compared to planktonic cultures, GAS organized in biofilms have higher MICs for all standard antibiotics used for treatment. Aim of this study was to investigate the ability of 30 Streptococcus pyogenes strains isolated from invasive infection to form biofilm. Biofilm experiments were performed in 96-well polystyrene microtiter containing THB. Experiments were perfomed in unmodified atmosphere, in atmosphere containing 5% CO2, and in anaerobiosis. The quantitative measurements was achieved by means of colorimetric methods using crytstal violet.The optical density of the biofilm was measured at 570 nm (OD570) by the calculation of adherence index. 80% of strains were biofilm formers: 15 strains under anaerobic conditions, 16 strains under aerobic condition and 19 strains in atmosphere containing 5% CO2. Moreover, 30% of these strains were bioflim former in all conditions, 20% in air and contemporarily in atmosphere additioned of CO2, while 13.3% in anaerobiosis only, 6.7% in atmosphere additioned of CO2 only, 6.7% in anaerobiosis and contemporarily in atmosphere additioned of CO2 , and 3.3% in air only.