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

OJEDA-SANA A.M.; CÁCERES GUIDO P.A.; LOPARDO H.; PRADA F.; BALBARREY Z. ; VAN BAREN C.; MORENO S.

Rosario

Congreso; SAMIGE; 2013

Sociedad Argentina de Microbiologia General

With the increase in antibiotic-resistant bacteria and the lack of new antibiotics being brought onto the market, alternative strategies need to be found to deal with infections resulting from drug-resistant bacteria. A possible solution may be to combine existing antibiotics with phytochemicals to enhance the efficacy of antibiotics. Previously, we reported the in vitro antimicrobial activity of rosemary plants in the form of both essential oils and extracts.1,2 In addition, the antibiotic activity of rosemary oil with high amounts of α-pinene and 1.8-cineole against multidrug-resistant strains as a nosocomial S. aureus resistant to methicillin (MRSA) was reported.3 Our current interest is to study the antibacterial mechanisms of action, including possible synergistic effects with classical antibiotics on multidrug-resistant bacteria as MRSA and Klebsiella pneumoniae strains. Infections caused by these pathogens have limited treatment options and have been associated with high mortality rates. Results showed that α-pinene having in vitro a modest activity against MRSA, was able to enhance the antibiotic mupirocin at subinhibitory concentrations of a-pinene plus mupirocin (¼ MICs). Synergistic type of interaction between the two compounds was achieved. Moreover, the combination of both compounds in a dermal infection model of mice showed better in vivo efficacy when compared with the commercially available formulation of mupirocin alone. Histological appearance of skin after biopsy of specimens after treatments were performed and samples stained with Brown and Brenn to identify bacterial colonies and with hematoxylin to detect changes in the tissues. Specimens treated with α-pinene showed slight mixed inflammation in dermis and hypodermis and without or with minimal isolated bacteria on the murine skin. Other results were obtained using 1,8-cineole against the Gram-negative human pathogen Klebsiella pneumoniae sensible and resistant strains. This compound has a permeabilization effect on the cell membrane of the Gram-negative bacteria Escherichia coli1. In this work, data revealed low or null values of inhibition percentage by 1,8-cineole against K pneumoniae strains, but interestingly a clear permeabilizing effect by the Sytox green assay was observed on a carbapenem-resistant strain of K pneumoniae. Later, we tested if 1,8-cineol, is able to improve the activity of  antibiotics carbapenem or meropenem against this multiresistant strain. Indeed, after incubation with the monoterpene the sensitivity to both antibiotics was increased. Thus, α-pinene and 1,8-cineole, main antimicrobial compound of rosemary essential oils, showed inhibitory effects alone and in combination with common antibiotics on susceptible and multidrug resistance bacteria. Therefore, these rosemary compounds have a great potential in the treatment/prevention of bacterial strains that become resistant to conventional antibiotics. 1Ojeda-Sana et al, 2013  Food Control 31:189-195. 2Moreno et al, 2006 Free Rad. Res. 40:223?231. 3Cáceres et al, 2012. Pediatric Research 72(1):109