In vitro bacteriostatic activity of Origanum vulgare, Cymbopogon citratus, and Lippia alba essential oils in cat food bacterial isolates

Abstract

The pet industry is currently expanding and specializing mainly in the field of domestic felines. Problems related to antimicrobial resistance are frequent, and the use of essential oils (EOs) in animal feed has become a novel treatment strategy. Thus, the objective of this study was to assess the bacteriostatic activity of Brazilian lemon balm (Lippia alba), lemon grass (Cymbopogon citratus), and oregano (Origanum vulgare) in bacterial isolates from 12 samples of cat food sold in bulk. The EOs from fresh leaves of crops were obtained from the Medicinal Garden of Paranaense University, Umuarama, Paraná. Cat food samples were processed for identification of gram-positive and gram-negative microorganisms. The determination of the bacteriostatic activity of the EOs was performed by determination of the minimum inhibitory concentration (MIC) at dilutions of 2.5, 1.25, and 0.62 mg/mL. The diffusion disc technique was used to evaluate the resistance profile to the main antimicrobials used in the feline clinic and to analyze the effect of the association of these antimicrobials with the EOs studied. A total of 23 isolates were obtained, of which 16 were gram-negative and seven were gram-positive. As for the oil composition for L. alba, C. citratus, and O. vulgare, 40, 24, and 44 compounds were identified, respectively, with the major ones being geranial, geranial/?-citral, and carvacrol, respectively. Regarding MIC, no differences were found for any EOs tested. The lowest MIC value was obtained for the C. citratus EO (0.83 mg/mL) for two bacteria (coagulase-negative Staphylococcus and Corynebacterium kutscheri). The means of the inhibition halos for the 10 antimicrobials tested in association or not with one of the EOs for Klebsiella aerogenes, Proteus vulgaris, and Serratia rubidaea showed that, for S. rubidaea, the inhibition halo diameter (12.4 mm) was greater (p < 0.05) when amoxicillin was associated with the O. vulgare EO than the association of the same antibiotic with the C. citratus EO (11.0 mm). For K. aerogenes and P. vulgaris, there was no difference in inhibition halo diameter when EOs were included. In conclusion, L. alba, C. citratus, and O. vulgare EOs are effective in inhibiting the growth of gram-positive and gram-negative bacteria and can be added to cat food to replace chemical antimicrobials.