Project 3: In vitro PK-PD modeling of antibiotic interactions with P. aeruginosa biofilms

Confocal microscope images of live and dead stained Pseudomonas aeruginosa biofilms
(photos by Sun Ho Kim).

Conventional susceptibility testing methods measure the ability of a static concentration of a single antibiotic to inhibit the growth of a suspension of actively dividing bacterial cells. However, in actuality, treatment of CF airway infection exposes bacterial populations to multiple, concurrently administered antibiotics at concentrations that vary owing to distribution within and elimination from the body. In addition, P. aeruginosa in the CF airway form self-adherent biofilm communities of infrequently dividing bacterial cells that display much greater antibiotic resistance than is measured through conventional testing. Thus, conventional susceptibility testing does not accurately simulate the dynamics of CF airway infection and antibiotic treatment, leading to the paradox of “susceptible” yet non-eradicable P. aeruginosa.

In this study, an in vitro system in which microbes grown as biofilms are exposed to one or more antibiotics at concentrations that vary or cycle over time will be characterized, refined, and validated. The purpose of the in vitro system is to model the drug-pathogen interactions that occur when antibiotics are used to treat biofilm infections in vivo, and to mimic the appearance and disappearance of these drugs in the systemic circulation and at the site of action. The in vitro system will facilitate real-time measurement of time-dependent antibiotic concentrations (pharmacokinetics, or PK) as well as the effects of these antibiotics on microbial survival, growth, physiology, and antibiotic resistance (pharmacodynamics, or PD). Conditions within the in vitro system such as bacterial inoculum, nutrient availability, and antibiotic dosing and clearance will be adjusted to simulate in vivo conditions based on actual patient data using patient bacterial samples. In addition, computer-based mathematical modeling and simulation of clinical and in vitro PK-PD time courses will be used to refine the in vitro system.

The long-term clinical goal is to combine state-of-the-art biofilm culture methods, in vitro PK-PD modeling, and computer-based PK-PD modeling in order to predict antimicrobial and anti-biofilm effects of varying antibiotic dosing regimens and to estimate the accuracy of conventional antibiotic susceptibility testing methods.

Current collaborators on this project include Drs. Jane Burns, Matthew Parsek, and Gail Anderson of the University of Washington, and Dr. George Drusano of the Ordway Research Institute in Albany, NY.

Click here to go to Project 4: The Zebrafish embryo as a model of P. aeruginosa systemic infection.

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