Propionibacterium acnes Recovered from Atherosclerotic Human Carotid Arteries Undergoes Biofilm Dispersion and Releases Lipolytic and Proteolytic Enzymes in Response to Norepinephrine ChallengeIn Vitro
In the present study, human atherosclerotic carotid arteries were examined following endarterectomy for the presence of the Gram-positive bacteriumPropionibacterium acnesand its potential association with biofilm structures within the arterial wall. TheP. acnes16S rRNA gene was detectable in 4 of 15 carotid artery samples, and viableP. acneswas one among 10 different bacterial species recoverable in culture. Fluorescencein situhybridization analysis of 5 additional atherosclerotic carotid arteries demonstrated biofilm bacteria within all samples, withP. acnesdetectable in 4 samples. We also demonstrated that laboratory-grown cultures ofP. acnesbiofilms were susceptible to induction of a biofilm dispersion response when challenged with physiologically relevant levels of norepinephrine in the presence of iron-bound transferrin or with free iron. The production and release of lipolytic and proteolytic extracellular enzymes byP. acneswere shown to increase in iron-induced dispersed biofilms, and these dispersion-inducedP. acnesVP1 biofilms showed increased expression of mRNAs for the triacylglycerol lipases PPA2105 and PPA1796 and the hyaluronate lyase PPA380 compared to that in untreated biofilms. These results demonstrate thatP. acnescan infect the carotid arteries of humans with atherosclerosis as a component of multispecies biofilms and that dispersion is inducible for this organism, at leastin vitro, with physiologically relevant levels of norepinephrine resulting in the production and release of degradative enzymes.