Enterotoxigenic Staphylococcus aureus strains that were isolated from foods were investigated for their ability to develop direct-tolerance and cross-tolerance to sodium chloride (NaCl), potassium chloride (KCl), lactic acid (LA) and acetic acid (AA) after habituation in sublethal amounts (1/2 of the minimum inhibitory concentration - 1/2 MIC and 1/4 of the minimum inhibitory concentration - 1/4 MIC) of Origanum vulgare L. essential oil (OVEO). The habituation of S. aureus to 1/2 MIC and 1/4 MIC of OVEO did not induce direct-tolerance or cross-tolerance in the tested strains, as assessed by modulation of MIC values. Otherwise, exposing the strains to OVEO at sublethal concentrations maintained or increased the sensitivity of the cells to the tested stressing agents because the MIC values of OVEO, NaCl, KCl, LA and AA against the cells that were previously habituated to OVEO remained the same or decreased when compared with non-habituated cells. These data indicate that OVEO does not have an inductive effect on the acquisition of direct-tolerance or cross-tolerance in the tested enterotoxigenic strains of S. aureus to antimicrobial agents that are typically used in food preservation.

Candida albicans é um fungo comensal que circunstancialmente pode causar infecções superficiais das mucosas, como a estomatite protética, na qual o biofilme se forma sobre a superfície das próteses dentárias. Este estudo avaliou a viabilidade celular de biofilmes de C. albicans frente à ação antifúngica do timol em comparação com o miconazol por meio da técnica de fluorescência, empregando os corantes SYTO 9 e iodeto de propídio, e contagem das unidades formadoras de colônia. Utilizaram-se cepas de C. albicans (ATCC 11006). As concentrações inibitórias mínimas (CIM) e fungicidas mínimas (CFM) das drogas foram determinadas com testes de microdiluição em caldo, sendo o inóculo padronizado para corresponder a 0,5 da escala de McFarland (106 UFC/mL). Os biofilmes foram cultivados sobre a superfície de discos de resina acrílica, em células paralelas de fluxo, a partir de caldo Sabouraud suplementado com dextrose 10%. Para a contagem das unidades formadoras de colônia, as soluções fúngicas foram sequencialmente diluídas e semeadas em agar Sabouraud dextrose Os dados foram analisados por meio de estatística ANOVA A dois fatores e teste de Tukey (α = 5%). Biofilmes tratados com o timol e miconazol apresentaram baixos números percentuais de células viáveis nos tempos de exposição avaliados. Houve diferença estatística significante (p<0.05) em comparação com o controle, e o valor médio dos tempos de exposição entre miconazol e timol não diferiu estatisticamente (p>0.05). Concluindo, ambas as drogas possuem similar eficiência como agentes antifúngicos contra a viabilidade de biofilmes de C. albicans formados em superfícies de resinas acrílicas.

Candida albicans is a commensal fungus, but circumstantially it may cause superficial infections of the mucous membranes, such as denture stomatitis, when a biofilm is formed on the surface of dental prostheses. This study evaluated the cell viability of C. albicans biofilms against the antifungal activity of thymol when compared with miconazole, by the fluorescence imaging using SYTO 9 and propidium iodide dyes, and counting of colony forming units. C. albicans standard strains (ATCC 11006) were used. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of drugs were determined by broth microdilution tests and the inoculum was standardized to match 0.5 on the McFarland scale (106 cfu/mL). Biofilms were grown on the surface of acrylic resin disks in parallel flow chambers from Sabouraud broth supplemented with 10% dextrose. For counting of colony forming units, the fungal solution was sequentially diluted and plated in Sabouraud dextrose agar. Data were analyzed using two-way ANOVA and Tukey's test (a=5%). Biofilms treated with thymol and miconazole presented low numbers of viable cells at the evaluated exposure times. There was statistically significant difference (p<0.05) when compared with control, and the mean value of the exposure times between miconazole and thymol did not differ significantly (p>0.05). In conclusion, both drugs have similar efficiency as antifungal agents against biofilms of C. albicans formed on acrylic surfaces.