aureus and S. epidermidis generated biofilms. AKBA is reported to be

active against a large number of inflammatory diseases, cancer, arthritis, chronic colitis, ulcerative colitis, Crohn’s disease, and bronchial asthma [21, 26, 20, 27, 28]. The anticancer activity of AKBA is attributed to the inhibitory effect on the lipoxygenases leading to the inhibition PLX3397 chemical structure of cell proliferation and induction of apoptosis in tumor cells [29]. There are numerous reports available on the antibacterial activity of oleo-gum resin extracts and oleo-gum resin essential oils from Boswellia spp. (Burseraceae) [30–32]. Weckessera et al. [33] reported the antibacterial activity of Boswellia dry extract and keto-ß-boswellic acid. Their findings revealed that the extract was highly effective against selected aerobic and anaerobic bacteria such as Streptococcus, Corynebacteria, C. perfringens and P. acnes; whereas KBA was not effective against these pathogens, suggesting that the effective components are other boswellic acids or essential oils contained in the extract. In this study, we extensively evaluated the boswellic acids for the antibacterial activity and further for the first time established that AKBA is the single most potent antibacterial compound

present in the gum exudates of Boswellia serrata. We further investigated the effect of AKBA on the bacterial cell membrane integrity through propidium iodide uptake assay. Propidium iodide is fluorescent nucleic acid stain that

binds to DNA by intercalating between the bases with little or no sequence preference. It is membrane impermeant and generally excluded from viable cells. The increased uptake of propidium AZD2281 mouse iodide in the AKBA treated cells of S aureus in our study indicated that AKBA altered the cell membrane structure, resulting in the disruption of the permeability barrier of microbial membrane structures. Leakage of cytosolic constituents (260 and 280 nm absorbing materials) from S. aureus cells in the presence 64 μg/ml AKBA over a period of two h was significantly higher than background levels (P < CYTH4 0.05). These observations indicate that the antimicrobial activity of AKBA results from its ability to disrupt the permeability barrier of microbial membrane structures. The lack of antibacterial activity of AKBA against Gram-negative bacteria may be attributed due to the presence of lipophilic outer membrane. This outer layer of the Gram-negative outer membrane is composed primarily of lipopolysaccharide molecules and forms a hydrophilic permeability barrier providing protection against the effects of highly hydrophobic compounds [34, 35]. This may be the probable explanation of the resistance of Gram-negative bacteria to lipophilic AKBA. Similar observations have been made in other studies also, where lipohilic terpenes such as carvacrol, thymol, eugenol, geraniol, linalyl acetate, (-) menthol and bakuchiol have reported low sensitivities against Gram-negative bacteria [36–38].