Antibacterial activity of plant extracts obtained by two methods against pathogens of clinical importance in veterinary medicine

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This study aimed to determine the antibacterial activity of different plant extracts against ATCC-type pathogens of importance to veterinary medicine. Extracts were obtained using the Soxhlet and hydroalcoholic extraction method. Each requires different conditions, and these methods will likely afford different biological activities. Hence, results were compared to determine the influence of the extraction process, particularly against the antibacterial activity of the extracts of Origanum vulgare, Rosmarinus officinalis, Psidium guajava, Thymus vulgaris, Eysenhardtia polystachya, Cinnamomum zeylanicum, and Syzygium aromaticum. All extracts were assessed for antibacterial activity against gram-positive bacteria (Staphylococcus aureus, Bacillus cereus, and Bacillus subtilis) and gram-negative bacteria (Escherichia coli, Salmonella enterica serotype Typhi). The agar well diffusion method was performed, and MICs were determined by the broth microdilution method. From all plant primary extracts tested, results show that the antibacterial action vs. gram-positive bacteria was greatest for the hydroalcoholic extracts of Origanum vulgare, Thymus vulgaris, and Psidium guajava, and again, Psidium guajava and Eysenhardtia polystachya for the Soxhlet extracts. Only the Soxhlet extract of Eysenhardtia polystachya showed a well-defined antibacterial action vs. gram-negative bacteria, although results do not exceed the reference drug utilized (enrofloxacin). It is proposed that research on the use of the mentioned extracts alone or combined with antibiotics in veterinary medicine follows, as well as the isolation and quantification of secondary metabolites present.