Anti-enterococcal activities of pentacyclic triterpenes

Background. Asiatic (AA) and ursolic (UA) acids are widely studied phytochemicals, but their antimicrobial properties are still poorly understood. Therefore our research has focused on their activity against uropathogenic Enterococcus faecalis strains. Objectives. The aim of this research was to determine the influence of AA and UA on the growth, cell morphology, virulence factors and biofilm formation by E. faecalis strains. Material and methods. AA and UA were purchased from Sigma-Aldrich. E. faecalis strains were isolated from the urine samples of patients with urinary tract infections. The strains were checked for the presence of virulence genes using the PCR method. Their antimicrobial susceptibility was performed using the disc diffusion method. The MICs of triterpenes were determined using the broth microdilution method. The hydrophobicity of cells was established by salt aggregation test. Lipase and lecithinase activities were determined by using an agar medium containing egg yolk emulsion. DNase agar was used for the detection of DNase synthesis. Hemolytic activity was established using a sheep-blood agar. Todd-Hewitt agar medium containing gelatin was used for determination of gelatinase activity. The anti-biofilm activity of asiatic acid and ursolic acid was tested on polystyrene microtiter plates. It was examined using time-kill and biofilm assays. Results. Reduction of growth and enzyme synthesis after exposure of E. faecalis to the acids was observed. None of the acids changed the hydrophobicity of bacteria. Stronger anti-biofilm activity was observed when the bacteria were incubated with AA. Thus, reduction of both the survival and the virulence factors will make bacteria less infectious. Conclusions. Based on the results obtained, we can assume that the triterpenes investigated should be considered natural components of a human diet rather than as antibacterial agents used on their own.