Modelling experimentally measured of ciprofloxacin antibiotic diffusion in Pseudomonas aeruginosa biofilm formed in artificial sputum medium

Abstract

We study the experimentally measured ciprofloxacin antibiotic diffusion through a gel-like artificial sputum medium (ASM) mimicking physiological conditions typical for a cystic fibrosis layer, in which regions occupied by Pseudomonas aeruginosa bacteria are present. To quantify the antibiotic diffusion dynamics we employ a phenomenological model using a subdiffusion-absorption equation with a fractional time derivative. This effective equation describes molecular diffusion in a medium structured akin Thompson’s plumpudding model; here the ‘pudding’ background represents the ASM and the ‘plums’ represent the bacterial biofilm. The pudding is a subdiffusion barrier for antibiotic molecules that can affect bacteria found in plums. For the experimental study we use an interferometric method to determine the time evolution of the amount of antibiotic that has diffused through the biofilm. The theoretical model shows that this function is qualitatively different depending on whether or not absorption of the antibiotic in the biofilm occurs. We show that the process can be divided into three successive stages: (1) only antibiotic subdiffusion with constant biofilm parameters, (2) subdiffusion and absorption of antibiotic molecules with variable biofilm transport parameters, (3) subdiffusion and absorption in the medium but the biofilm parameters are constant again. Stage 2 is interpreted as the appearance of an intensive defence build–up of bacteria against the action of the antibiotic, and in the stage 3 it is likely that the bacteria have been inactivated. Times at which stages change are determined from the experimentally obtained temporal evolution of the amount of antibiotic that has diffused through the ASM with bacteria. Our analysis shows good agreement between experimental and theoretical results and is consistent with the biologically expected biofilm response. We show that an experimental method to study the temporal evolution of the amount of a substance that has diffused through a biofilm is useful in studying the processes occurring in a biofilm. We also show that the complicated biological process of antibiotic diffusion in a biofilm can be described by a fractional subdiffusion-absorption equation with subdiffusion and absorption parameters that change over time.

The Antibacterial Effect of PEGylated Carbosilane Dendrimers on P. aeruginosa Alone and in Combination with Phage-Derived Endolysin

“…The diffusion of cationic CBS dendrimers (4, 7) through PAO1 biofilm was determined experimentally using the laser interferometry method [45][46][47]. A biofilm of PAO1 was formed in TSB (tryptic soy broth) medium for 72 h in stationary conditions at 37 • C on a PET membrane with pores of diameter 1 µm as an element of BD Falcon™ Cell Culture Inserts.…”

Pseudomonas aeruginosa Consumption of Airway Metabolites Promotes Lung Infection

“…However, pathogenesis studies using clinical isolates illustrate the very substantial differences between these laboratory organisms that reflect properties of environmental strains of P. aeruginosa or those taken from the blood stream, versus the organisms that have undergone adaptive changes to long term survival in the human airway [9,21,41,54,55]. Similar discrepancies are observed in the media used to mimic the host airway for in vitro P. aeruginosa studies, especially in CF; artificial media containing DNA and mucin reflect many of the conditions expected in the airway but fail to include the major immune cell metabolites, succinate and itaconate or provide ROS that are an inherent component in vivo conditions [56][57][58][59]. The CF airway undoubtedly contains many other immunometabolites and components not yet characterized.…”

Experimental and Theoretical Analysis of Metal Complex Diffusion through Cell Monolayer

“…These conditions depend on the probabilities of a particle passing across the thin membrane and the kind of diffusion in the considered system. For example, in the case of subdiffusion (this process occurs in many biological processes, such as antibiotics transport in a bacterial biofilm [17,25]), the mean time that a particle waits to take its next step is infinite, as opposed to the diffusion process in which this time is finite. This means that the frequencies of a particle's attempts to pass across the membrane for these processes are described by qualitatively different functions; for subdiffusion, this frequency is significantly lower than for normal diffusion.…”

“…In practice, the derivation of N(t) for the system considered in this paper is analogous with the derivation of a similar function in the system in which antibiotics diffuse across the bacterial biofilm [17,25].…”

“…Laser interferometry was previously used by us to test various theoretical models of diffusion, to study membrane substance transport, to determine membrane transport parameters under concentration polarization conditions, to analyze anomalous diffusion (subdiffusion) in gel systems, and to probe hydrodynamic instability [15][16][17][18]. After various modifications, we also employed laser interferometry to test the release and interactions of macromolecules with biologically active substances, such as bacterial liposaccharide (LPS) endotoxin with colistin, chitosan and saponin [19][20][21].…”