Browsing by Author "Grobe, Katherine Jean"

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Investigation of biofilm resistance to antimicrobial agents
(Montana State University - Bozeman, College of Engineering, 1999) Grobe, Katherine Jean
Modeling biofilm antimicrobial resistance
(2000-05) Dodds, Michael G.; Grobe, Katherine Jean; Stewart, Philip S.
A computer model capable of integrating mechanisms of biofilm resistance to disinfection by antimicrobial agents was developed. Resistance mechanisms considered included retarded penetration due to a stoichiometric reaction between the antimicrobial agent and biomass, incomplete penetration due to a catalytic reaction between the antimicrobial agent and the biomass, and the existence of a fraction of the cells in a resistant phenotypic state. Mathematical models of these processes were derived and solved in the computer simulation package MATLAB. Four sets of fitted experimental data on the disinfection of Pseudomonas aeruginosa biofilms were fit to each of the three models. No one model fit all of the data sets adequately. Killing of a 2-day old biofilm by tobramycin was best described by the physiological limitation model. Killing by hypochlorite was best described by the stoichiometric transport model. Killing by hydrogen peroxide was best simulated by the catalytic transport model. These results suggest that multiple mechanisms of biofilm reduced susceptibility are manifested even in biofilms of the same species and that the particular resistance mechanism depends on the biofilm age, antimicrobial agent, and biofilm thickness. The models presented in this article may be useful for diagnosing mechanisms of biofilm resistance from experimental data.
Role of dose concentration in biocide efficacy against pseudomonas aeruginosa biofilms
(2002-07) Grobe, Katherine Jean; Zahller, Jeff; Stewart, Philip S.
Pseudomonas aeruginosa entrapped in alginate gel beads to form artificial biofilms resisted killing by chlorine, glutaraldehyde, 2,2-dibromo-3-nitrilopropionamide (DBNPA), and an alkyl dimethyl benzyl ammonium compound (ADBAC). The degree of resistance was quantified by a resistance factor that compared killing times for biofilm and planktonic cells in response to the same concentration of antimicrobial agent. Resistance factors averaged 120 for chlorine, 34 for glutaraldehyde, 29 for DBNPA, and 1900 for ADBAC. In every case resistance factors decreased with increasing concentration of the antimicrobial agent. An independent analysis of the concentration dependence of the apparent rates of killing of planktonic and biofilm bacteria showed that elevating the treatment concentration increased bacterial killing more in the biofilm than it did in a suspension culture. Calculation of a transport modulus comparing the rates of biocide reaction and diffusion suggested that at least part of the biofilm resistance to chlorine, glutaraldehdye, and DBNPA could be attributed to incomplete or slow penetration of these agents into the biofilm. Time-kill curves were nonlinear for biofilm bacteria in some cases. The shapes of these curves implicated retarded antimicrobial penetration for chlorine and glutaraldehyde and the presence of a tolerant subpopulation for DBNPA and ADBAC. The results indicate that treating biofilms with a concentrated dose of biocide is more effective than using prolonged doses of a lower concentration.