AIM: This review highlights the anti-staphylococcal activities of pentacyclic triterpenoids, particularly α-amyrin (AM), betulinic acid (BA) and betulinaldehyde (BE). These compounds are based on a 30-carbon skeleton comprising five six-membered rings (ursanes and lanostanes) or four six-membered rings and one five-membered ring (lupanes and hopanes).
METHODS: Electronic databases such as ScienceDirect, PubMed and Scopus were used to search scientific contributions until March 2018, using relevant keywords. Literature focusing on the antimicrobial and antibiofilms of effects of pentacyclic triterpenoids on S. aureus were identified and summarized.
RESULTS: Pentacyclic triterpenoids can be divided into three representative classes, namely ursane, lupane and oleananes. This class of compounds have been shown to exhibit analgesic, immunomodulatory, anti-inflammatory, anticancer, antioxidant, antifungal and antibacterial activities. In studies of the antimicrobial activities and targets of AM, BA and BE in sensitive and multidrug-resistant S. aureus, these compounds acted synergistically and have different targets from the conventional antibiotics.
CONCLUSION: The inhibitory mechanisms of S. aureus in novel targets and pathways should stimulate further researches to develop AM, BA and BE as therapeutic agents for infections caused by S. aureus. Continued efforts to identify and exploit synergistic combinations by the three compounds and peptidoglycan inhibitors, are also necessary as alternative treatment options for S. aureus infections.
OBJECTIVE: This review highlights the challenges and potential in using current technologies in the discovery and development of novel antibacterial agents to keep up with the constantly evolving resistance in bacteria.
CONCLUSION: With the explosion of bacterial genomic data and rapid development of new sequencing technologies, the understanding of bacterial pathogenesis and identification of novel antibiotic targets have significantly improved.
OBJECTIVE: This study was carried out to evaluate the ability of the three compounds to significantly reduce the biomass of pre-formed biofilms of MRSA and metabolic activity of the bacterial cells in the biofilm.
METHODS: The anti-biofilm activity of α-amyrin, betulinic acid and betulinaldehyde, individually and in combination with oxacillin or vancomycin, against reference strain of MRSA in pre-formed biofilm were evaluated using the crystal violet and resazurin assays.
RESULTS: α-amyrin and betulinic acid significantly reduced the biomass of pre-formed biofilms of MRSA as individual compounds and in combination with oxacillin or vancomycin. Although betulinaldehyde individually increased the biomass, selected combinations with oxacillin and vancomycin were able to reduce the biomass. All three compounds did not show cytotoxic properties on normal mammalian cells.
CONCLUSION: The three pentacyclic triterpenoids could significantly reduce pre-formed biofilm of MRSA with no cytotoxic effects on normal mammalian cells. These findings demonstrated that pentacyclic triterpenoids have the potential to be developed further as antibiofilm agents against MRSA cells in biofilms, to combat infections caused by multidrug-resistant and biofilm-forming S. aureus.
METHODS: The antimicrobial activity was tested against the planktonic S. aureus cells using the microdilution broth assay, while the antibiofilm activity were evaluated using the crystal violet and resazurin assays. The cytotoxicity of the SBDs was assessed on MRC5 (normal lung tissue), using the MTT assay.
RESULTS: The individual SBDs showed significant reduction of biomass and metabolic activity in both S. aureus strains. Combinations of the SBDs with OXA and VAN were mainly additive against the planktonic cells and cells in the biofilm. Both the compounds showed moderate toxicity against the MRC5 cell line. The selectivity index suggested that the compounds were more cytotoxic to S. aureus than the normal cells.
CONCLUSION: Both the SBD compounds demonstrated promising antimicrobial and antibiofilm activities and have the potential to be further developed as an antimicrobial agent against infections caused by MRSA.