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The influence of various concentrations (0.003-8 mg/mL) of N-acetylcysteine on the formation of biofilms by 15 strains of Staphylococcus epidermidis has been studied. A dose-related decrease in biofilm formation was observed, except with the lowest concentrations. The 'slime' index relative to the control was 63%, 55%, 46%, 34%, 26% and 26% in the presence of 0.25, 0.5, 1, 2, 4, and 8 mg/mL of N-acetylcysteine, respectively. These data are statistically significant. The inhibitory effect of 2 mg/mL of N-acetylcysteine on slime formation was also verified by electron microscopy.

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Candida tropicalis is an emerging virulent species. The aim of this study is to determine the biofilm-forming ability of 29 strains of C. tropicalis isolated from inpatients, and to examine its relation with other virulence factors such as cellular surface hydrophobicity (CSH), immediate (15 min, IA) and late (24 h, LA) plastic adherence and filamentation ability. The study was performed in parallel using two incubation temperatures -37 and 22°C -to determine the effect of growth temperature variations on these pathogenic attributes of C. tropicalis. Biofilm formation (BF) was measured by optical density (OD) and by XTT reduction (XTT); Slime index (SI), which includes growth as a correction factor in BF, was calculated in both methods. All strains were hydrophobic and adherent -at 15 min and 24 h -at both temperatures, with higher values for 22°C; the adhered basal yeast layer appears to be necessary to achieve subsequent development of biofilm. Filamentation ability varied from 76.2% of strains at 37°C to 26.6% at 22°C. All C. tropicalis strains were biofilm producers, with similar results obtained using OD determination and XTT measurement to evaluation methods; SI is useful when good growth is not presented. BF at 37°C was similar at 24 h and 96 h incubation; conversely, at 22°C, the highest number of biofilm-producing strains was detected at 96 h. CSH is an important pathogenic factor which is involved in adherence, is influenced by the filamentation of yeast, and plays a critical role in BF.

Aims: The aim of this study is to determine the in vitro activity of allicin against Staphylococcus epidermidis and to evaluate the influence of allicin on biofilm formation. Methods and Results: In vitro activity of allicin (diallyl thiosulphinate) against 38 strains of S. epidermidis was investigated. The activity of allicin was similar against S. epidermidis methicillin susceptible and methicillin resistant strains [minimum inhibitory concentration (MIC) 90 ¼ 8 mg l)1 ]. In general, subinhibitory concentrations (sub-MIC) of allicin diminished biofilm formation in the five strains analysed. Conclusion:The results confirm the antibacterial effect of allicin. Sub-MICs of allicin also diminished the biofilm formations by S. epidermidis. Significance and Impact of the Study: The present study shows that allicin is active in vitro against S. epidermidis and that sub-MICs of allicin may play a role in the prevention of adherence of this bacteria to medical devices.

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The purpose of this work was to study the adhesion to polystyrene of two Candida parapsilosis strains, grown at 22 and 37°C, in terms of hydrophobicity, surface charge, and interaction free energy. Growth temperature changed the surface properties of microorganisms, yielding a good correlation between thermodynamic predictions and adhesion behavior.Candida parapsilosis has emerged as an important nosocomial pathogen (16,20,24) with clinical implications, all of which usually occur in association with invasive procedures or prosthetic devices (27). Colonization by candidas and subsequent infection is achieved by a combination of specific (ligand-receptor interactions) and nonspecific mechanisms (1), allowing the yeast to attach to a wide range of tissue types and nonbiological surfaces. This process depends on the cell surface properties of both the host and the fungus (4).The main nonspecific forces acting during the initial stages of the adhesion process have a thermodynamic nature, and they are mainly related to the hydrophobic effect (11). The contribution of the electrostatic forces to adherence has been questioned (12).Quantification of surface hydrophobicity and surface charge can be made by different methods (3,21,26), but the obtained results are greatly influenced by the environmental conditions in which cells are grown or suspended in experimental procedures (7,8,9,10,19).The aim of this work is to study the hydrophobicity and surface charge of C. parapsilosis in relation to the process of adhesion to polystyrene, in order to determine whether the thermodynamic theory predicts the adherence. The effect of growth temperature on the above properties has been also analyzed.C. parapsilosis strain 294 and C. parapsilosis strain 289 were isolated from blood of patients of Infanta Cristina Hospital (Badajoz, Spain). Yeasts were stored at Ϫ80°C and cultured in Sabouraud broth at 22 and 37°C for 48 h. After culture, the yeasts were harvested by centrifugation, 5 min at 1,000 ϫ g (Sorvall TC6; Dupont, Newtown, Conn.), and washed three times in deionized water, potassium phosphate buffer (KPi) (0.01 mol liter Ϫ1 ) or phosphate-buffered saline (PBS) (0.1 mol liter Ϫ1 ) depending on the liquid employed in the experimental hydrophobicity assay. Finally, the cells were resuspended in the appropriate fluids.Water, formamide, and diiodomethane contact angles ( W , F , and D , respectively) on lawns of partially dried yeasts were determined using the sessile drop technique (3) ( Table 1). Briefly, microorganisms suspended in demineralized water were layered onto 3-m-pore-size filters (Millipore; Molsheim, France) using a negative pressure. The filters were left to air dry for 30 min and introduced into an environmental chamber, which was allowed to saturate with vapor from the liquid employed. The images were taken as has been described previously (15). Once the contact angles were measured, the Lifshitz-van der Waals (␥ LW ) and acid-base (␥ AB ) surface tension components were obtained from the application of the You...