Antibacterial Efficacy of well-known antibiotics potentiated by Rosmarinus officinalis compounds against nosocomial meticillin-resistant Staphylococcus aureus (MRSA) and carbapenem-resistant Klebsiella pneumoniae (CRKP) strains

OJEDA SANA A.M; PAULO ARTURO C¨¢CERES GUIDO; ALEJANDRA BLANCO; HORACIO LOPARDO; ZIOMARA BALBARREY; FEDERICO PARRA ; CATALINA VAN BAREN; SILVIA MORENO

Rosario, Prov de Santa Fe

Congreso; IX Congreso de Microbiología General; 2013

Sociedad Argentina de Microbiolog¨ªa General

With the increase in antibiotic-resistant bacteria and the lack of new antibiotics, alternative strategies need to be found to deal with infections resulting from drug-resistant bacteria. A possible solution is to combine existing antibiotics with phytochemicals to enhance the efficacy of antibiotics. Previously, we reported the in vitro antimicrobial activity of rosemary essential oils with high amounts of a-pinene and 1,8-cineole and extracts.1-3 Our current interest is to analyze the antibacterial mechanisms of action and synergistic effects of rosemary compounds effective against MRSA and CRKP. Antibacterial activity was determined by the broth microdilution method and permeabilizing effects by the green fluorescent nucleic acid dye Sytox green. In vivo studies were performed in a superficial skin infection model in mice and skin biopsies were stained with Brown and Brenn to identify bacterial colonies, and with hematoxylin-eosin to evaluate changes in the tissues. Results showed that a-pinene had a modest in vitro activity against MRSA, however potentiated the well-known antibiotic with a synergistic type of interaction. Also, in vivo topical treatment of a-pinene inhibited the superficial infection caused by a nosocomial MRSA strain in the skin of BALB/c mice. Specimens treated with a-pinene showed slight mixed inflammation in dermis and hypodermis without or with minimal isolated bacteria on the corneal layer of epidermis. Moreover, the combination of a-pinene with antibiotic in the animal model showed better efficacy when compared with the commercial antibiotic, reducing the bacterial growth in near 4-5 log10 compared with the vehicle treatment. Later, we evaluated the effect of 1,8-cineole on K. pneumoniae strains. Results indicated that this monoterpene slightly affect the bacterial growth of the both strains: susceptible and CRKP, however after incubation at 2.5 microl/ml-1 the compound caused an increase in the fluorescence of Sytox green of near 50% and 28%, respectively. This concentration corresponded to 1/8 X MIC of 1,8-cineole against the susceptible strain. Importantly, this concentration was capable to enhance the percentages of inhibition of the ertapenem of 5% to 20% and the meropenem from 23% to 41% against the CRKP strain. Therefore, the 1,8-cineole  improved the potency of these b-lactam-type antibiotics probably by altering the permeability of the plasma membrane. In conclusion, our findings support a potential use of both compounds of rosemary essential oils, in combination with other drugs as a possible therapeutic antibacterial agent in the treatment/prevention of bacterial strains that become resistant to conventional antibiotics.1Ojeda et al. 2013 Food Control 31:189-195. 2Moreno et al. 2006 Free Rad Res 40:223¨C231. 3C¨¢ceres et al. 2012 Pediatric Res 72(1):109.