October 29, 2015

In a recent paper in PLOS One we report the results of a study that we performed with (and was funded by) Novartis.  The report builds on a previous finding that the addition of mannitol could enhance the activity of the antibiotic tobramycin versus biofilms of some strains of Pseudomonas aeruginosa grown on abiotic surfaces.  This was an important finding because mannitol can be delivered to the lung of cystic fibrosis patients, and thus might help treat these chronic infections. Here, we looked at whether we could detect enhancement of killing of P. aeruginosa biofilms from on CF-derived airway cells.  We've shown previously that biofilms in this model have key traits of biofilms grown on abiotic surfaces, but importantly, biofilms on CF airway cells show increased antibiotic tolerance versus biofilms grown on abiotic surface.  The bottom line of our study is encapsulated in the title of the manuscript: "Mannitol Does Not Enhance Tobramycin Killing of Pseudomonas aeruginosa in a Cystic Fibrosis Model System of Biofilm Formation".  Using lab strains and several clinical isolates of P. aeruginosa we saw no increased killing of these biofilms upon mannitol addition.

I just attended the ASM Biofilms Conference in Chicago.  It was a fun and informative meeting, and I had the opportunity to catch up with former post-docs from the lab.  From left to right are Mary Ellen Davey (an Assistant Professor at the University of Florida), Yun Luo (a group leader at Dupont), and Thien-Fah (Thienny) Mah who is an Associate Professor at the University of Ottawa.

Also, there will be a special issue of JB the will highlights papers related to this meeting - look for it in 2016.

October 22, 2015

My lab has had a growing interest in the impact of polymicrobial communities on bacterial biology and the response of microbes to antibiotic in such communities.  We have focused our studies on polymicrobial communities that we have identified and characterized in the lungs of patients with cystic fibrosis.  In a paper recently published the Journal of Bacteriology in a study headed up by Katie Price (left, a former postdoc in the lab), we examined the consequences of growing Pseudomonas aeruginosa with another CF lung pathogen, Streptococcus constellatus, in the context of CF-derived airway cells.  This report shows that rhamnolipids produced by P. aeruginosa PA14 can reduce the viability of S. constellatus 7155.  Interestingly, when this co-culture is treated with tobramycin, a front-line antibiotic in CF, this rhamnolipid-mediated killing by P. aeruginosa PA14 is eliminated because tobramycin appears to inhibit rhamnolipid production.  While this interaction is specific for these two strains, conceptually this study illustrates the point that the behavior of microbes in mixed communities cannot be easily predicted from their growth in mono-culture.  These findings also show a basic approach for studying mechanisms underlying polymicrobial interactions in the context of host cells.