Resumo

The incidence of resistance to antibiotics increase, so research to find new products with antimicrobial activity is very important to decrease morbidity and mortality. Schiff base is an organic compound formed by condensation of amine and an aldehyde or ketone. The present study aimed to report the antibacterial and antibiotic modifying activity of the Schiff Base N,N-bis(salicylidene)-1,2-phenylenediamine. Microorganisms used for the determination of antibacterial activities were Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 15442, Escherichia coli ATCC 10536 and Klebsiella pneumoniae ATCC 4362. The minimal inhibitory concentration (MIC) was determined in a microdilution assay using 96-well microplates. The compound was added in the first well-microplates containing inoculum suspended in brain heart infusion broth and were made serial 2-fold dilutions in a concentration of the Schiff base range of 8-512µg/mL. Microplates incubated for 24h at 37 ºC. A resazurin reagent was used to indicate the presence of uninhibited bacterial growth (pink colour) or inhibition (blue colour). For the evaluation of the effect the Schiff base as modulators of resistance to the antibiotic used the aminoglycosides: amikacin, gentamicin, neomycin and used the bacterial strains: P. aeruginosa 03, S. aureus 358, E. coli 27. The modulation was determined in a same microdilution and colorimetric assay of the previous experiment. MIC of the antibiotics was determined in the presence or absence (control) of compound at subinhibitory concentrations (64 µg/mL), inoculum of each strain and the antibiotic concentration range of 1.22-2,500 µg/mL. The MIC of the Schiff Base was 512 µg/mL for all strains tested, such there was no difference sensitivity to the compound between the bacterial evaluated. The antibiotic activity of amikacin against S. aureus and E. coli (39 and 19.5 µg/mL) was enhanced in the presence of the product compared to control, while showed no effect on gentamicin and neomycin activity. Against P. aeruginosa was observed no antibiotic modifying activity by Schiff Base. In conclusion, the Schiff Base showed synergism when combined with amikacin against the S. aureus and E. coli. Therefore, the compound could be used as adjuvant to antibiotic therapy against these pathogens.