Susceptibility of biofilm forming Pseudomonas aeruginosa and Staphylococcus aureus to antibiotic-adjuvants

Aims: The objective of the present study is to evaluate the possibility of reversing the resistance of pathogens to antibiotics using phytochemicals from plant extracts as antibiotic-adjuvant. Methodology and results: Twenty-one plants were collected from Podhigai Hills, Tamil Nadu, India and tested in this study. The susceptibility of burn wound isolates (Pseudomonas aeruginosa and Staphylococcus aureus) to antibiotics and the adjuvant activity of the aqueous plant extracts were tested using well diffusion assay. The impact of the plant extracts on quorum sensing was assessed using Chromobacterium violaceum as the model organism. The antibiofilm activity of the adjuvant and antibiotics was determined by crystal violet assay. The isolates which were resistant to more than one class of antibiotics (aminoglycoside, cephalosporin, fluoroquinolone and penicillin) were designated as multidrug resistant bacteria. Combination of cefdinir-Citrullus colocynthis showed 17 mm inhibition zone which is greater than cefdinir (0 mm) against P. aeruginosa. The combination reduced quorum sensing with an inhibition zone of 30 mm. The same combination reduced 96% and 95% of the biofilm formed by P. aeruginosa and S. aureus, respectively at 16 h. Besides, cefdinir with Leucas aspera reduced quorum sensing with an inhibition zone of 28 mm. The combination reduced 94% and 95% of biofilm formed by P. aeruginosa and S. aureus, respectively at 16 h. The aqueous extract of C. colocynthis and L. aspera revealed the presence of flavonoids that possess adjuvant activity. Conclusion, significance and impact of study: Cefdinir-C. colocynthis and cefdinir-L. aspera reversed the resistance of multi drug resistant bacteria to cefdinir. The flavonoids of C. colocynthis and L. aspera served as an adjuvant that potentiates the activity of cefdinir.