Susceptibility to Thrombin-Induced Platelet Microbicidal Protein Is Associated with Increased Fluconazole Efficacy against Experimental Endocarditis Due to Candida albicans

Abstract

Platelet microbicidal proteins (PMPs) are believed to be integral to host defense against endovascular infection. We previously demonstrated that susceptibility to thrombin-induced PMP 1 (tPMP-1) in vitro negatively influences Candida albicans virulence in the rabbit model of infective endocarditis (IE). This study evaluated the relationship between in vitro tPMP-1 susceptibility (tPMP-1 s ) or resistance (tPMP-1 r ) and efficacy of fluconazole (FLU) therapy of IE due to C. albicans. Candida IE was established in rabbits with either tPMP-1 s or tPMP-1 r strains. Treatment groups received FLU (100 mg/kg/day) intraperitoneally for 7 or 14 days; control animals received no therapy. At these time points, cardiac vegetations, kidneys, and spleens were quantitatively cultured to assess fungal burden. At both 7 and 14 days and in all target tissues, the extent of candidal clearance by FLU was greater in animals infected with the tPMP-1 s strain than in those infected with the tPMP-1 r strain. These differences were statistically significant in the spleen and kidney. Corroborating these in vivo data, FLU (a candidastatic agent), in combination with tPMP-1, exerted an enhanced fungicidal effect in vitro against tPMP-1 s and tPMP-1 r C. albicans, with the extent of this effect greatest against the tPMP-1 s strain. Collectively, these results support the concept that tPMP-1 susceptibility contributes to the net efficacy of FLU against C. albicans IE in vivo, particularly in tissues in which platelets and tPMP-1 likely play significant roles in host defense.

SSD1 Is Integral to Host Defense Peptide Resistance in Candida albicans

“…C. albicans ATCC 36082, originally a clinical isolate, was previously determined to be susceptible to the antimicrobial peptide tPMP-1 (tPMP-1 S ; strain 36082 S ) (41). A stable tPMP-1-resistant and orthogenic coun-terpart (tPMP-1 R ) of strain 36082 S , designated strain 36082 R , has been characterized previously (42,43). Prior studies demonstrated that other than in differences in tPMP-1 susceptibility profiles, the 36082 S and 36082 R strains are indistinguishable by genotyping and immunotypic profiling, assessment of endothelial cell adhesion, and metabolic, germination, or growth rate characteristics (41)(42)(43).…”

“…Prior studies demonstrated that other than in differences in tPMP-1 susceptibility profiles, the 36082 S and 36082 R strains are indistinguishable by genotyping and immunotypic profiling, assessment of endothelial cell adhesion, and metabolic, germination, or growth rate characteristics (41)(42)(43). Studies have also confirmed that the tPMP-1 S and tPMP-1 R phenotypes are stable in vitro following passage in media or serum and upon passage through experimental animal models (42,43). Moreover, prior investigations in vivo confirmed that these strains are equivalent in their interactions with platelets or cardiac vegetations and do not differ in rates of clearance after hematogenous inoculation in experimental animal models (9,42).…”

“…A stable tPMP-1-resistant and orthogenic coun-terpart (tPMP-1 R ) of strain 36082 S , designated strain 36082 R , has been characterized previously (42,43). Prior studies demonstrated that other than in differences in tPMP-1 susceptibility profiles, the 36082 S and 36082 R strains are indistinguishable by genotyping and immunotypic profiling, assessment of endothelial cell adhesion, and metabolic, germination, or growth rate characteristics (41)(42)(43). Studies have also confirmed that the tPMP-1 S and tPMP-1 R phenotypes are stable in vitro following passage in media or serum and upon passage through experimental animal models (42,43).…”

“…These investigations demonstrated that the peptide-resistant strain C. albicans 36082 R proliferated in cardiac vegetations and spleen to densities logarithmically higher than those seen for the orthogenic and peptide-susceptible counterpart, 36082 S . Moreover, subsequent studies revealed that fluconazole was significantly less efficacious in reducing tissue burden due to strain 36082 R than in reducing that due to strain 36082 S (42). Differences in fungal growth rates, levels of adherence to vascular endothelium, levels of clearance from the bloodstream, and susceptibilities to fluconazole were ruled out as potential confounders of the above results.…”

“…Prior studies have examined the relationship between resistance to thrombin-induced platelet microbicidal protein-1 (tPMP-1) and C. albicans virulence in the rabbit model of infective endocarditis (42). These investigations demonstrated that the peptide-resistant strain C. albicans 36082 R proliferated in cardiac vegetations and spleen to densities logarithmically higher than those seen for the orthogenic and peptide-susceptible counterpart, 36082 S .…”