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The inhibitory and bactericidal activities of anacardic acid and totarol, alone and in combination with methicillin, were investigated against methicillin-resistant Staphylococcus aureus (MRSA). The growth of two MRSA strains was inhibited by 6 x 25 microg ml-1 of anacardic acid and 0 x 78 microg ml-1 of totarol. The time-kill curve study showed that these two compounds were bactericidal against MRSA. Anacardic acid killed MRSA cells more rapidly than totarol, and no viable cells were detected after being exposed to 6 x 25 microg ml-1 of anacardic acid for 6 h. Anacardic acid showed bactericidal activity against MRSA at any stage of growth, and also even when cell division was inhibited by chloramphenicol. In the combination studies, the minimal inhibitory concentration (MIC) of methicillin was lowered from 800 to 1 x 56 microg ml-1 for MRSA ATCC 33591, and from 800 to 6 x 25 microg ml-1 for MRSA ATCC 33592, by combining with 1/2 x MIC of anacardic acid. The time-kill curves demonstrated synergistic bactericidal activities for these combinations.

Antimicrobial activity of six diterpenoids isolated from the bark of Podocarpus nagi (Podocarpaceae) has been tested against twelve selected microorganisms. Totarol [1], the most abundant compound among the six, exhibited potent bactericidal activity only against Gram-positive bacteria, among which Propionibacterium acnes was the most sensitive bacterium. Totarol also showed strong activity against four other Gram-positive bacteria tested: Streptococcus mutans, Bacillus subtilis, Brevibacterium ammoniagenes, and Staphylococcus aureus (both penicillin-resistant and penicillin-susceptible strains). The bactericidal activity of totarol was enhanced when it was tested in combination with several other natural products. Noticeably, the activity of totarol against Sta. aureus was increased eightfold when tested in combination with 1/2MIC of anacardic acid [9]. The synergistic activity of anacardic acid caused the minimum bactericidal concentration (MBC) of totarol to be lowered from 1.56 to 0.2 micrograms/ml.

The 10 major volatile constituents were identified by GC-MS analysis as common flavor principles in mate tea obtained from various locations. Their antimicrobial activity against 13 microorganisms was tested. All of the volatiles tested exhibited moderate to weak activity with broad spectra. Some of them are bactericidal against one of the most important cariogenic bacteria, Streptococcus mutans. The antibacterial activity of the distillate against S. mutans was significantly enhanced by indole.