The released fatty acids are thought to be inflammatory; they favor 5-Fluoracil ductal hypercornification and increase adhesion between P. acnes and cells of the hair follicle, promoting colonization of P. acnes and biofilm formation [37, 40–42]. Furthermore, GehA itself is a strong chemotactic factor . Other secreted esterases identified include a putative lysophospholipase (PPA2142) and a putative phosphoesterase (PPA1498) with unknown specificities. Proteases, another class of secreted
hydrolases, were also detected, e.g. a peptidase S8/S53 family protein (PPA0598) among others; their substrate specificities remain to be elucidated. CAMP factors and other secreted proteins A set of five highly similar P. acnes genes (PPA687, PPA1198, PPA1231, PPA1340,
PPA2108) in the genome of P. acnes KPA encodes homologs to Christie-Atkins-Munch-Petersen (CAMP) factors, which are co-haemolytic proteins, found mainly in streptococcal species [25, 44, 45]. CAMP factors have been characterized as pathogenic determinants that exert lethal effects when administered to rabbits and mice . In addition, streptococcal CAMP factors have been reported to act as pore-forming toxins . In agreement with previous work , all P. acnes strains examined here were positive for the co-haemolytic CAMP reaction (data not shown). Our secretome data showed that all tested P. acnes strains secreted CAMP2 (PPA0687). In selleck inhibitor addition, the skin isolate KPA secreted CAMP4 (PPA1231). Secretion of the other three CAMPs was not observed in any strain heptaminol using our approach. A previous study reported variable production of CAMP factors in different P. acnes isolates, as detected by western blotting experiments using different anti-CAMP sera ; the authors reported an abundance of CAMP1 in type IB and II strains.
We did not find CAMP1 among the secreted proteins; a discrepancy that could be due to the detection limits of the different techniques used, i.e. our MS analysis detects the most prominently secreted factors, whereas immunoblotting is a more sensitive technique. A key enzyme of glycolysis, GAPDH, was also secreted by three out of the five P. acnes strains tested. At first glance it is peculiar why a glycolysis enzyme should be secreted; however, a number of studies have identified GAPDH as an anchorless, multifunctional protein, displayed on the surface of several fungi and Gram-positive pathogens, which contributes to adhesion and virulence [48, 49]. In Streptococcus pyogenes, this cell-associated and soluble protein is also known as streptococcal surface dehydrogenase (SDH) and as a plasmin receptor (Plr); its complement C5a-binding activity was shown to play a role in evasion of neutrophil recruitment to sites of infection . Moreover, in S. agalactiae, GAPDH is an immunomodulatory factor, exhibiting B lymphocyte-stimulatory activity .