Effect of Thyme Extract on E. coli and Salmonella in Cattle

Abstract

Background: The presence of antimicrobial resistance (AMR) in livestock-associated pathogens, specifically in Escherichia coli and Salmonella, poses a problem for public health, which calls for effective natural alternatives. Objective: The intent of this research is to assess the in vitro antimicrobial properties of Thymus vulgaris (thyme) extract on multi-drug-resistant Escherichia coli and Salmonella spp. from cattle. Methods: Fifty bacterial isolates (25 E. coli and 25 Salmonella spp.) from cattle farms were collected. T. vulgaris hydroalcoholic extract was prepared, and the antimicrobial effect was assessed with the agar well diffusion method at five concentrations (25, 50, 100, 150, 200 mg/mL). The broth microdilution method was applied to determine the MIC and MBC. We also performed polymerase chain reaction (PCR) to check for the invA gene for Salmonella and the stx1 gene for E. coli in the isolated strains. Results: Antimicrobial activity of thyme extract was significantly observed on all the isolates, and was concentration dependent. The mean inhibition zone diameters for E. coli and Salmonella were 15.4 ± 0.8 mm to 32.1 ± 1.2 mm and 16.2 ± 0.9 mm to 31.5 ± 1.1 mm respectively. The MIC ranged from 6.25 to 25 mg/mL and the MBC from 12.5 to 50 mg/mL for most of the isolates the thyme extract was bactericidal. All 25 Salmonella isolates (100%) were confirmed to have the invA gene, and 8 of 25 E. coli isolates (32%) were confirmed to have the stx1 gene. Conclusion: T. vulgaris extract has strong antimicrobial activity and effect along with the dose dependence on Salmonella spp. and E. coli, and provides support for use as a natural feed amendment. Thus, it holds promise as a potential feed alternative for reducing AMR.