BIOFILM PRODUCTION BY CANDIDA BLOODSTREAM ISOLATES: PREVALENCE AND CORRELATION WITH PATIENTS’ OUTCOME

Candida biofilm production on medical devices has been recognized as an increasing clinical problem. The Candida biofilm lifestyle results in antifungal drug resistance and protection of the fungus from host defences. However, discrepant results were obtained in studies correlating in vitro biofilm forming ability and clinical outcome of candidemia (Tumbarello et al. JCM 2007; Shin et al. JCM 2002). The aims of the present study were: 1) To investigate the prevalence of biofilm producers among Candida bloodstream isolates from intensive care unit (ICU) patients; 2) To correlate the biofilm production with patients’ outcome. Material and Methods. A total of 297 Candida bloodstream isolates collected during the ECMM-FIMUA epidemiological study on deep-seated Candida infections in ICU patients (2006-2008) were studied. Biofilm formation was determined as described by Ramage et al. (AAC 2001). Briefly, 100 μL of yeast suspension in RPMI 1640 broth were inoculated in flat-bottom 96-well microtitre plates. Biofilm production was measured after 24h by using the 2,3-bis (2-methoxy-4-nitro-5-sulphophenil)-2H-tetrazolium-5-carboxanilide (XTT) reduction assay. The absorbance was read spectrophotometrically at 490 nm. The percentage transmittance (%T), calculated from absorbance, was inversely proportional to the cellular density of the biofilm. Biofilm production was scored as 6+ (%T ≤ 5), 5+ (%T 6–10), 4+ (%T 11–20), 3+ (%T 21–40), 2+ (%T 41–60) or 1+ (%T > 60). The test was done in triplicate. Isolates showing scores of 6+ or 5+ were considered high producers of biofilm, and those with scores of 1+ or 2+ were considered poor producers. The relationship between biofilm formation (high vs poor) and patient outcome at day 30 after diagnosis of candidemia was measured by odds ratio (OR). Results. 32.3% (96 out of 297 tested blood isolates) exhibited a high biofilm forming ability, namely 55.5% of C. tropicalis isolates, 34% of C. albicans, 26% C. glabrata, and 23 % of C. parapsilosis isolates. A similar mortality rate was observed in patients with infection due to high and poor biofilm producer C. albicans (18/45, 40% vs 6/16, 37.5%, OR 1.11) as well as non albicans Candida isolates (19/32, 59.3% vs 59.4%, OR 1.017). Conclusions. The rate of high biofilm producers among Candida bloodstream isolates is relevant, but this characteristic does not seem to be a significant predictor of mortality in this patient population.