Effect of host-mimicking medium and biofilm growth on the ability of colistin to kill Pseudomonas aeruginosa

Abstract

In vivo biofilms cause recalcitrant infections with extensive and unpredictable antibiotic tolerance. Here, we demonstrate increased tolerance of colistin by Pseudomonas aeruginosa when grown in medium that mimics cystic fibrosis (CF) sputum versus standard medium in in vitro biofilm assays, and drastically increased tolerance when grown in an ex vivo CF model versus the in vitro assay. We used colistin conjugated to the fluorescent dye BODIPY to assess the penetration of the antibiotic into ex vivo biofilms and showed that poor penetration partly explains the high doses of drug necessary to kill bacteria in these biofilms. The ability of antibiotics to penetrate the biofilm matrix is key to their clinical success, but hard to measure. Our results demonstrate both the importance of reduced entry into the matrix in in vivo-like biofilm, and the tractability of using a fluorescent tag and benchtop fluorimeter to assess antibiotic entry into biofilms. This method could be a relatively quick, cheap and useful addition to diagnostic and drug development pipelines, allowing the assessment of drug entry into biofilms, in in vivo-like conditions, prior to more detailed tests of biofilm killing.

Microbial Musings – January 2021

“…I seem destined to not write about papers coming out of Freya Harrisons’ (@friendlymicrobe) lab at the University of Warwick, UK, as her new paper in this month’s issue has been selected as the Editor’s Choice for January. This remarkable achievement follows a previous paper from the same first author Esther Sweeney (@SweeneyEsther) which was published just last month [19]. In her new paper Esther, working with clinicians Matthew Hurley (@MatthewNHurley) and Alan Smyth (@AlanRSmyth) at the University of Nottingham, along with Marwa Hassan (@DrMarwa_Hassan) and Niamh Harrington (@_NiamhEllen) with other colleagues in Nottingham, have made further progress using a porcine lung model they developed previously [20], to now demonstrate that this also functions as a suitable model for studying how Staphylococcus aureus grows during chronic infections of the cystic fibrosis lung [21].…”

Antibiotic Efficacy Testing in an Ex vivo Model of <em>Pseudomonas aeruginosa</em> and <em>Staphylococcus aureus</em> Biofilms in the Cystic Fibrosis Lung

“…This can be quantified using standard repeatability calculations after ANOVA 25 ; we have found that there is typically greater variation between CFU in replicate lung samples for S. aureus than for P. aeruginosa. We recommend that, on adoption of the model by a laboratory, repeat calculations are conducted on pilot experiments to optimize experimental techniques and to determine samples sizes to be used in final experiments (an example of this may be found in the data supplement for Sweeney et al 26 ).…”

Phage-Derived Depolymerase as an Antibiotic Adjuvant Against Multidrug-Resistant Acinetobacter Baumannii

“…These suggested that using depolymerases as a stand-alone treatment might not be sufficient in controlling infections associated with biofilms. Impairing drug diffusion (subdiffusion) within the biofilm matrix is a major contributor to the sub-optimal treatment to biofilm related infections [48]. Improving the antibiotics penetration into the biofilm matrix may hold the key to better clinical outcomes.…”