Human pathogens have readily been converted into multidrug-resistant pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA), because of the long-term use of conventional antibiotics. In addition, the biofilms formed by S. aureus cells are especially problematic and are related to the persistence of chronic infections because they constitute a major mechanism of promoting tolerance to diverse antimicrobial agents. Hence, the inhibitions of biofilm formation and/or toxin production are accepted as alternative means of controlling S. aureus infections. The present study was aimed at identifying novel anti-biofilm and/or anti-virulence compounds in friedelane-based pentacyclic triterpenoids present in many edible and medicinal plants—and investigating them against MRSA strains. As a result, dihydrocelastrol and dihydrocelastryl diacetate were found to both inhibit the biofilm formation of, and to disrupt the preformed biofilms of, MRSA strains to an increasingly greater degree with increasing concentrations of each compound. Furthermore, these two triterpenoids also clearly inhibited the hemolytic activity of MRSA—and in-line with their anti-biofilm activities, rendered the cell more hydrophilic. Additionally, corroborating phenotypic results, transcriptional analyses showed that both dihydrocelastrol and dihydrocelastryl diacetate disturbed the expression of gene related to α-hemolysin (hla) and down-regulated the expressions of the crucial biofilm-associated genes (agrA, sarA, ica, RNAIII, and rbf) in MRSA. The findings of this study suggest that friedelane-based pentacyclic triterpenoids—especially dihydrocelastrol and dihydrocelastryl diacetate—have the potential to be candidates both for use in controlling biofilm-related infections and for use as important components of anti-virulence strategies for fighting against MRSA infection.
