Abstract
The present study aimed to evaluate Syzygium aromaticum (clove) plant extract, clove oil and eugenol for their antibacterial activity and their potential to eradicate bacterial biofilms alone and in combination with antibiotics. Anti-bacterial efficacy of S. aromaticum extract, clove oil and eugenol was evaluated as minimum inhibitory concentration (MIC) and subsequently sub-MICs was selected for inhibition of virulence factors against test bacterial strains. Biofilm cultivation and eradication was assayed using XTT reduction in 96-well microtiter plate. Checkerboard method was used to study the interaction between essential oils and antibiotics. Staphylococcus aureus MTCC3160, Staphylococcus epidermidis MTCC435, Staphylococcus sciuri (SC-01), Staphylococcus auricularis (SU-01) and Streptococcus mutans MTCC497 were found strong biofilm former among all the test bacterial strains. The potency of test agents was found in the order of eugenol > clove oil > S. aromaticum methanolic extract. Sub-MIC (0.5 × MIC) of clove oil and eugenol showed a significant reduction in cell surface hydrophobicity (p S. auricularis (SU-01), S. epidermidis MTCC435 and S. mutans MTCC497 compared to planktonic MIC (PMIC). Antibiotics (vancomycin and azithromycin) exhibited upto 1000-folds increased in SMIC compared to PMIC against all the test bacterial strains. Synergy was observed between eugenol and antibiotics (vancomycin/azithromycin) against all the test bacterial strains in both planktonic and sessile mode. Highest synergy was exhibited between eugenol and azithromycin in planktonic mode (FICI value 0.141). Further, microscopy also confirmed the spectacular effect of combination treatment on pre-formed S. aureus MTCC3160 and S. mutans MTCC497 biofilms. These findings highlighted the promising role of clove oil and eugenol alone and in combination on pathogenic bacterial biofilms.
Highlights
Infectious diseases are still a major global cause of mortality and morbidity in humans mainly in developing countries
Anti-bacterial efficacy of S. aromaticum extract, clove oil and eugenol was evaluated as minimum inhibitory concentration (MIC) and subsequently sub-MICs was selected for inhibition of virulence factors against test bacterial strains
Eugenol showed no increase in sessile MIC (SMIC) against S. auricularis (SU-01), S. epidermidis MTCC435 and S. mutans MTCC497 compared to planktonic MIC (PMIC)
Summary
Infectious diseases are still a major global cause of mortality and morbidity in humans mainly in developing countries. Many opportunistic and drug resistant pathogenic bacterial species that are widely studied include Staphylococcus and Streptococcus species [1]. The tendency of these bacteria to cause infections is often related to the expression of several virulence factors, such as cell surface hydrophobicity, hemolysin production and biofilm formation. The involvement of Streptococcus mutans in oral biofilm associated infections is well known As long as these bacterial species adhere and form multilayered biofilms on host tissues and different surfaces, it persists and prolongs the infections [9]. Several advantages may be expected through this approach, such as less chance of emergence of resistance, improved efficacy of single drug in combination and dose related toxicity [12] [13]
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