Potential of N-acetylcysteine as an adjuvant to amoxicillin against mastitis-associated Staphylococcus aureus and Escherichia coli.

Bovine mastitis is a major health and economic problem in dairy animals, primarily caused by bacterial pathogens such as Staphylococcus aureus, Streptococcus spp. and Escherichia coli. The rise of antimicrobial resistance has reduced the effectiveness of conventional antibiotics, emphasizing the need for alternative or adjunct treatment strategies. The present study evaluated the in vitro synergistic antimicrobial activity of amoxicillin in combination with N-acetylcysteine (NAC) against virulent isolates of S. aureus and E. coli recovered from clinical bovine mastitis cases. Antimicrobial susceptibility test was conducted using disc diffusion test, and the interaction between amoxicillin and NAC was assessed through a qualitative minimum inhibitory concentration test strip method and quantitative checkerboard assay. The combination of amoxicillin and NAC exhibited enhanced antibacterial activity compared to amoxicillin alone, indicating a synergistic effect against the virulent S. aureus and E. coli. Qualitative analysis revealed an increased zone of inhibition with the combination treatment relative to individual agents. Quantitative findings showed a 32-fold reduction in MIC for S. aureus and E. coli. The improved antimicrobial efficacy attributed to the antibiofilm and mucolytic properties of NAC, which can disrupt biofilm architecture and enhance antibiotic penetration. Overall, the findings suggest that NAC serve as a potential adjuvant to conventional antibiotic therapy for improved management of mastitis caused by resistant bacterial pathogens.