Inhibitory and Microbicidal Activity of Larrea divaricata extracts

MATTANA CM; CIFUENTE DA; MOHAMED AM

Milazzo

Congreso; XXVII Italo-Latin American Congress of Ethnomedicine; 2018

SILAE

IntroductionThe increase of microbial resistance to antibiotics affects the control of clinical infections and constitutes a growing concern in the world public health. This situation, as well as the appearance of undesirable effects of certain antibiotics, has led to the investigation of new antimicrobial substances from vegetable species popularly used in folk medicine. In this context the activity of Larrea divaricata Cav. was tested, a plant species commonly known as ?jarilla? collected in the province of San Luis, Argentina. It was designated as ?natural jarilla?. In addition, the same plant obtained from a local herbalist, called ?commercial jarilla? was tested.Methods We worked with the aerial part of the plant. The collected plant material was air dried and crushed in knife mills until fine granulometry. The pulverized material was extracted with organic solvents of different polarity at room temperature and at higher temperatures, by means of the following procedures: soxhlet-methanol (1), soxhlet-n-hexane (2), lixiviation-chloroform (3), aqueous (4), maceration- ethyl acetate (5), maceration-acetone (6), lixiviation-ethanol (7) for the commercial plant; and the same processes for the natural one: soxhlet-methanol (8), soxhlet-n-hexane (9), lixiviation-chloroform (10), aqueous (11), maceration- ethyl acetate (12), maceration-acetone (13), lixiviation-ethanol (14). The 14 previously obtained extracts were diluted in appropriate concentrations, taking as starting concentration 20 mg/ml. The MIC was performed in duplicate in a flat-bottom 96-well plate, aliquoting 150 μl of culture medium supplemented with 2,3,5-triphenyltetrazolium chloride as a visual growth indicator, 10 μl of the bacterial inoculum (105 cfu/ml) and 150 μl of dilutions of the extracts. The MIC was interpreted as the minimum concentration of extract that inhibited the microbial growth visualized by yellow color. The strains tested were: Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 35218, Staphylococcus aureus ATCC 29213, Staphylococcus epidermidis ATCC 12228, Listeria monocytogenes CLIP 74904, Candida albicans ATCC 36801. Culture media, extracts and microbial inocula were included as control. The plates were incubated at 37 ° C for 24 h. Then, the Minimum Microbicide Concentration (MMC) was determined, subculturing 10 μl aliquots of the previous culture on a plate containing trypticase soy agar and incubating 24 h at 37 ° C. The absence of development indicated microbicidal activity.Results/Discussion/ConclusionAll the microorganisms tested were inhibited in their development, both prokaryotic cells (Gram-positive and Gram-negative bacteria) and eukaryotic cells (yeasts). Gram-negative bacteria (P. aeruginosa and E. coli) showed greater resistance to the different extracts. Concentrations between 0.625 and 5 mg/ml were required to achieve inhibitory effect (MIC) for commercial jarilla and between 0.625 and 10 mg/ml for natural jarilla. Microbicidal effect (CMM) was obtained with concentrations equal to the MIC or 2 x MIC. The highest bacteriostatic and bactericidal activity was observed in gram-positive bacteria (S. aureus, S. epidermidis and L. monocytogenes) with values between 0.312 and 2.5 mg/ml. C. albicans was inhibited at concentrations between 0.312 and 2.5 mg/ml and values between 5 and 0.312mg/ml showed microbicidal effect for yeast. The commercial and natural extracts presented better inhibitory activity for gramnegative bacteria. The extract 3 inhibited all tested strains with less concentration (≤0.312 mg/ml). The MIC of the commercial extracts 5, 6 and 7 was similar to the MIC of the respective natural extracts (12, 13 and 14). The extracts derived from L. divaricata are promising as future phytodrugs. Cytotoxic and genotoxic tests will be necessary to ensure their safety.