In vitro activity of prodigiosin isolated from serratia marcescens in combination with two groups of antibiotics against gram-positive microorganisms

Abstract

The work was aimed to study the synergy of the antimicrobial activity of the prodigiosin pigment with antibiotics against bacteria of the genera Bacillus, Staphylococcus and Streptococcus. The serial dilution method was used to evaluate antimicrobial compositions, which included inhibitors of cell wall synthesis: ampicillin, benzylpenicillin, vancomycin, cefazolin, and metronidazole (nitroimidazole derivatives) in combination with the pigment prodigiosin isolated from Serratia marcescens. Each combination was tested against the studied strains. The fractional inhibitory concentration index (FICI) for each combination was calculated to determine synergy, and the results were interpreted as follows: FICI 0.5 — synergism; FICI> 4.0 — antagonism; and FICI> 0.5–4 — neutralism. It was shown that the ethanol extract of prodigiosin in combination with benzylpenicillin, vancomycin, cefazolin, and metronidazole interacted differently synergistically depending on the type of microorganism. The combinations of prodigiosin and metronidazole showed a synergistic effect against Bacillus subtilis, vancomycin and cefazolin against Staphylococcus aureus and benzylpenicillin against Streptococcus pyogenes. Other combinations of prodigiosin and antibiotics showed a neutral effect, and in the case of cefazolin against Str. pyogenes, even an antagonistic effect. Thus, the study showed the synergism of prodigiosin with antibiotics depending on the type of microorganism, contributed to a several-fold decrease in the minimum inhibitory and bactericidal concentrations of each component separately, and the results indicated that prodigiosin acted separately more efficiently against gram-positive non-spore-forming bacteria. This synergistic combination of antimicrobial agents had great potency to prevent bacterial resistance.