Browsing by Author "Garny, Kerstin"

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    Antimicrobial susceptibility and population dynamics of a defined biofilm community under different nutrient conditions
    (Stellenbosch : Stellenbosch University, 2004-03) Garny, Kerstin; Wolfaardt, Gideon M.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Little is known about the impact of nutrient conditions on antimicrobial resistance in biofilms grown under continuous flow conditions. Furthermore, community-level response of biofilms to antimicrobial substances and different nutrient regimes are poorly described. A better understanding of the influence of environmental conditions on biofilm behavior and antimicrobial susceptibility may contribute to the efforts, addressing the problems associated with increased antimicrobial resistance. Therefore, the aim of this study was to evaluate the survival and population dynamics in a defined mixed-species biofilm community grown under different nutrient conditions and when subjected to biocide treatment. Epi-fluorescence microscopy in conjunction with the LIVE/DEAD® BacLight™ viability kit, a conventional cultivation technique (plate counts), and culture-independent techniques (terminal restriction fragment length polymorphism and fluorescent in situ hybridization) were applied to observe biofilm and planktonic antimicrobial susceptibility, as well as population dynamics. A defined mixed-species community, consisting of four bacterial strains, was cultivated and monitored in a flow cell system. Two nutrient types were used: 1) a complex growth medium [tryptone soy broth (TSB)] and 2) a defined synthetic medium [minimal salts supplemented with glucose (MSM + Glucose)]. In addition, these two nutrient types were applied in different concentrations. Biofilm and planktonic community behavior was influenced by the nutrient type and concentration. Species evenness in the planktonic community was influenced by the nutrient conditions, while species richness changed in response to biocide treatment and nutrient conditions. TSB-grown microbial communities were more susceptible directly after biocide treatment than those grown in MSM + Glucose, however, biofilm viability in the latter nutrient condition decreased within 24 h after biocide treatment. Furthermore, a surprising difference in the recovery rate between biofilm and associated planktonic communities was observed. A conceptual model was developed that aimed to explain the observed biofilm-planktonic interactions. This model proposes that the cells found in the outer regions of a biofilm are the primary source of the associated planktonic cells, and that this phenomenon is independent from overall biofilm activity.