Avaliação do efeito antibacteriano do S-(-)-limoneno isolado e incorporado a nanoemulsão e nanoemulgel sobre cepas de Klebsiella pneumoniae

Abstract

Diseases related to pathogenic bacteria continue to be a significant threat to the human body. Among the main bacteria that cause infections, we find Klebsiella pneumoniae, which is associated with, among other conditions, infections in skin wounds such as pressure injuries. Thus, the antibacterial effect of S-(-)-limonene isolated and incorporated into nanoemulsion and nanoemulgel on Klebsiella pneumoniae strains was analyzed. For this purpose, the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of S-(-)- limonene against Klebsiella pneumoniae strains were determined using the microdilution technique on a Muller Hinton broth plate. The Minimum Inhibitory Concentration of Adhesion (MIC) was identified, the lowest concentration of the agent in contact with sucrose that prevented adhesion to the test tube. The association of S-(-)-Limonene with synthetic antibacterials was then evaluated by the disk diffusion method. Following the study, a nanoemulsion containing S-(-)-limonene was developed by the ultrasonication method with the addition of a gelling agent to the nanoemulsion. They were characterized in terms of droplet size and polydispersity index (PDI) by dynamic light scattering, as well as their macroscopic characteristics and pH. Subsequently, the antibacterial activity of the nanoemulsion was evaluated by MIC by the plate microdilution method and of the nanoemulgel incorporated with S-(-)-Limonene by the well diffusion method. The MIC50 of S-(-)- limonene was 1000 μg/mL, MBC above 1000 μg/mL and absence of antiadherence activity were obtained, as well as in the positive control with 0.12% chlorhexidine digluconate. The data from the association of S-(-)-Limonene with synthetic antimicrobials demonstrated synergistic, indifferent and antagonistic effects, where gentamicin presented a synergistic effect with most of the tested strains. Nanoemulsion (NE) and nanoemulgel (NG) containing 10% S-(-)-Limonene were formulated, with NE presenting greater stability of droplet size and PDI (47.47 nm and 0.2561, respectively) until day 90, and did not present macroscopic changes. NG showed an increase in droplet size and PDI after the thirtieth day. In the investigation of the MIC and MBC of the nanoemulsion incorporated with S-(-)-Limonene, the MIC50 was 1000 μg/mL, as well as in the isolated product. When performing the susceptibility test of K. pneumoniae strains to NG incorporated with S-(-)-Limonene, an antibacterial effect was observed, considering the formation of an inhibition halo of 20 mm. Thus, it is concluded that S-(-)-Limonene is a candidate for the development of new pharmacological technologies for the treatment of skin lesions infected with K. pneumoniae alone or in formulations with emulsified systems.