Resumo
Background: Mastitis is economically considered the most important disease in dairy cattle. Reports on the increase of organisms that are resistant to antimicrobial drugs, as well as on the demand for sanitary inputs which can be used in organic and agroecological animal production models motivate the research and discovery of new vegetal-based drugs for their control. The objective of this study was to evaluate the antibacterial activity of the galenic form decoction of Achyrocline satureioides (Lam.) D.C. - Asteracea ("macela") against standard and isolated bacteria found in bovine mastitis. Materials, Methods & Results: A. satureioides was collected from a single site and its exsiccate was identified and registered at the Instituto de Biociências of the UFRGS under number ICN 161.026. The decoction was obtained from the cooking of inflorescences with distilled water, with subsequent replacement of the evaporated volume. The solution was analyzed by thin layer chromatography (TLC) and the phytochemical quality was verified based on the presence of a flavonoid, quercetine. The antibacterial activity was evaluated using the pour plate technique, leaving the decoction in contact with the bacteria for 1 h and 24 h. After the pre-established contact times, the plates received ± 30 mL of a solid Mueller-Hinton culture medium without (reading of the bacterial inhibition indication) and with neutralizer (reading of the bacterial inactivation indication). It was observed a statistic significance (significant or not significant) of the solution's microbiological effect in reducing the population density, compared to the bacterial cultivation on plate containing culture medium without decoction. Initially, Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 11229 were tested in 3 proportions plant : volume, with a proportion of 7.5 g : 100 mL, demonstrating higher inactivation ability. The decoction was tested with 23 bacteria isolated from the milk of cows with mastitis, of which 20 were Gram positive (14 Staphylococcus aureus, 5 Streptococcus dysgalactiae, 1 Streptococcus uberis) and 3 Gram negative (1 Escherichia coli, 1 Klebsiella sp. and 1 Pseudomonas aeruginosa). In 100% of the microorganisms, a significant reduction in the population density meant total absence of growth, both in plates with bacteriostatic action and with bacterial inactivation. In the 1-h contact reading, we could observe that 15 Gram positive bacteria were inhibited and one had already been inactivated; in the 24-h reading, three bacteria remained inhibited, but 18 had been inactivated. Three Staphylococcus isolates, inhibited in 1 h and 24 h, were not inactivated even with a 24-h contact time. The decoction did not have any activity against Gram negative bacteria with a 1-h contact time, but all were inactive after 24 h. Discussion: The presence of quercetine confirmed the phytochemical quality of the decoction solution, since this chemical group is thought to be responsible for the plant's biological activities. Chemical neutralizers inactivate antimicrobial substance residues after inoculum exposure. Mixing these compounds to the culture medium of one of the treatment plates was efficient, since it allowed the differentiation between inhibition and inactivation in plates containing the decoction, where no bacterial growth was observed. When comparing the activity on bacteria which had been subjected to in vitro antimicrobial susceptibility testing (AST), 8 were inactivated and one was inhibited by the decoction, out of 9 that were resistant to some antibiotic drug. Our conclusion was that the decoction of Achyrocline satureioides had an antibacterial action against all 25 bacterial inocula tested, inactivating 22 and inhibiting the growth of three.