In Vivo Efficacy of Antimicrobials against Biofilm-Producing Pseudomonas aeruginosa

Abstract

e Patients suffering from cystic fibrosis (CF) are commonly affected by chronic Pseudomonas aeruginosa biofilm infections. This is the main cause for the high disease severity. In this study, we demonstrate that P. aeruginosa is able to efficiently colonize murine solid tumors after intravenous injection and to form biofilms in this tissue. Biofilm formation was evident by electron microscopy. Such structures could not be observed with transposon mutants, which were defective in biofilm formation. Comparative transcriptional profiling of P. aeruginosa indicated physiological similarity of the bacteria in the murine tumor model and the CF lung. The efficacy of currently available antibiotics for treatment of P. aeruginosa-infected CF lungs, such as ciprofloxacin, colistin, and tobramycin, could be tested in the tumor model. We found that clinically recommended doses of these antibiotics were unable to eliminate wild-type P. aeruginosa PA14 while being effective against biofilm-defective mutants. However, colistin-tobramycin combination therapy significantly reduced the number of P. aeruginosa PA14 cells in tumors at lower concentrations. Hence, we present a versatile experimental system that is providing a platform to test approved and newly developed antibiofilm compounds.

Options and Limitations in Clinical Investigation of Bacterial Biofilms

“…Localized mammalian animal models may refer to skin and soft tissue infections experimentally studied by use of infected excisional wounds, partial-thickness abrasions, scratches, burns, abscesses, and surgical sites. Apart from the pathogen of interest, experimental variation can also include the mammalian host by alteration of its immunological state (5,266,(321)(322)(323)(324)(325)(326)(327)(328)(329)(330)(331)(332)(333)(334)(335)(336)(337)(338).…”

“…Moreover, the therapeutic potential of inhaled liposomal amikacin was tested in a P. aeruginosa rat lung infection model (330). P. aeruginosa biofilms formed on murine tumors have also been used to examine the efficacy of ciprofloxacin, colistin, tobramycin, and their combinations (331).…”

Insights into host–pathogen interactions from state‐of‐the‐art animal models of respiratory Pseudomonas aeruginosa infections

“…The tumor model thus provides a simple model to investigate physiological factors involved in biofilm formation or the influence of a coinfection (see below). Furthermore, the tumor model seems to be a valid and simplified system for research on the efficacy of antimicrobial compounds and novel treatment regimens .…”

Importance of flagella in acute and chronic Pseudomonas aeruginosa infections

“…Such subcutaneous tumour tissue is quickly colonized by the bacteria after intravenously infection of the mice. Biofilms develop within 24 h and the bacteria exhibit an in vivo transcriptional profile that resembles the in vivo transcriptional profile of P. aeruginosa residing in the cystic fibrosis lung (Komor et al, 2012;Pawar et al, 2015). To ensure that the near saturated Tn mutant libraries were fully represented in the input mutant pool, we adapted this tumour infection model and applied an inoculum of 5 × 10 6 bacteria intra-tumorally (it).…”

“…According to the gene expression profile of P. aeruginosa, the bacteria recognize this niche as a habitat similar to cystic fibrosis lungs (Bielecki et al, 2011). Consequently, residence of the bacteria in this neoplastic tissues leads to development of therapy-refractory biofilm infections (Crull et al, 2011;Komor et al, 2012;Pawar et al, 2015). Comparison of the in vivo selected mutant pools from both systems implies that the immune response of the host against the infectious agent rather than the expression of bacterial virulence traits modulates disease outcome and drives acuteness and duration.…”