Synergistic bactericidal profiling of prodigiosin extracted from Serratia marcescens in combination with antibiotics against pathogenic bacteria

Gohil, Nisarg; Bhattacharjee, Gargi; Singh, Vijai

The emergence of multidrug resistance (MDR) bacteria is on the rise and the situation has been worsening on each successive day, which is evident from the outpouring number of reports about how more and more pathogens are becoming resistant to even the third and fourth generations of antibiotics. Lately, combination therapies or drug synergy have been giving promising results in curbing infections since it delineates its action on multiple aspects as compared to monotherapies. In this study, we used prodigiosin, a bacterial pigment endowed with magnificent biological properties, in combination with six antibiotics to study its effect on Pseudomonas aeruginosa, Staphylococcus aureus and Chromobacterium violaceum. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of prodigiosin against the test organisms were determined and a checkerboard assay of prodigiosin with various antibiotics combinations was performed with an aim to abate antimicrobial resistance. MIC and MBC for prodigiosin were obtained in the range of 4–16 μg/mL, which was lower than that of most test antibiotics. Coupling of prodigiosin with other test antibiotics exhibited an excellent synergy profile against all test organisms and the effects were reported to be either synergistic or additive. In the case of S. aureus and C. violaceum, all combinations were found to be synergic, and remarkably for S. aureus, FBC index was reported to be as low as ≤0.25 with all tested antibiotics. Therefore, it is deduced that prodigiosin augments and intensifies the action of antibiotics, and results in a double-whammy against the emergence of MDR strains.