Seasonal variability of the antimicrobial activity of the essential oil of Lippia alba
Abstract
Lippia alba is a shrub of the Verbenaceae family, popularly known as lemon balm. It's essential oil is said to have broad-spectrum antimicrobial activity whose effectiveness varies according to its composition, which is influenced by both biotic and abiotic factors. The present study aimed to evaluate the antimicrobial effectiveness of oil taken from the leaves of L. alba collected at different times of the year, against microorganisms of importance in food. The oil, obtained by hydrodistillation, was tested against standard cultures of Pseudomonas aeruginosa, Salmonella choleraesuis, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes and Listeria innocua using agar diffusion techniques. The different sampling times had a big influence on the efficiency of the oil, which varied in relation to each microbial species. From December to February the best response was against S. aureus. Against L. monocytogenes, the oil was effective from June to August, while for L. innocua, the oil presented the same response for three periods of the year, differing only from March to May. Correlation of meteorological data for 2010 makes it possible to verify that characteristics typical of the period from December to February in the town of Paraipaba, in the Brazilian state of Ceará (high temperatures, long periods of sunshine and low rainfall) favoured the action of the oil against S. aureus. In turn, from June to August, seasonal conditions enhanced the action of the oil against L. monocytogenes and L. innocua.
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