Antibacterial effect of plant-derived antimicrobials on major bacterial mastitis pathogens in vitro

Area of Science:

• Veterinary Microbiology
• Natural Product Chemistry
• Antimicrobial Agents

Background:

• Bovine mastitis is a significant economic concern in the dairy industry, often caused by bacterial infections.
• Current antibiotic treatments face challenges like resistance and residues, necessitating the exploration of alternative therapies.
• Plant-derived compounds are increasingly investigated for their antimicrobial properties.

Purpose of the Study:

• To evaluate the antimicrobial efficacy of four plant-derived compounds: trans-cinnamaldehyde (TC), eugenol, carvacrol, and thymol.
• To determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against key bovine mastitis pathogens.
• To assess the bactericidal kinetics and in-milk persistence of trans-cinnamaldehyde.

Main Methods:

• Determination of MIC and MBC values for TC, eugenol, carvacrol, and thymol against *Streptococcus agalactiae*, *S. dysgalactiae*, *S. uberis*, *Staphylococcus aureus*, and *Escherichia coli*.
• Time-kill assays were performed to evaluate the bactericidal kinetics of TC at its MBC.
• Antimicrobial activity of TC in milk was assessed over a 14-day period.

Main Results:

• All four plant compounds demonstrated antimicrobial activity, with trans-cinnamaldehyde (TC) being the most potent.
• TC exhibited low MIC (0.05-0.1%) and MBC (0.4-0.45%) values against the tested pathogens.
• TC rapidly reduced bacterial loads in milk (4.0-5.0 log(10) cfu/mL within 12-24 hours) and maintained its activity for 14 days.

Conclusions:

• Trans-cinnamaldehyde possesses significant bactericidal activity against major bovine mastitis pathogens.
• The compound's efficacy and persistence in milk suggest its potential as a viable alternative or adjunct therapy.
• Further evaluation of TC for intramammary infusion in treating bovine mastitis is warranted.