Antibacterial activity of palmarosa oil significantly varies between Aeromonas veronii and Aeromonas caviae and exhibits selective action on tetracycline and sulfonamide resistant A. caviae

AIMS: To investigate the antibacterial activity of three (palmarosa, basil and rosemary) essential oils (EOs) on Aeromonas veronii and Aeromonas caviae, and determine minimum inhibitory concentration (MIC) of potent EO against tetracycline and sulfonamide resistant strains. METHODS AND RESULTS: Palmarosa oil (PMO) showed significantly (p < 0.05) higher inhibition zones against both A. veronii and A. caviae (n = 30) than basil and rosemary in the disk diffusion assay. The MIC (% v/v) of PMO ranged from 0.008% to 1.00%. The mean MIC was significantly higher for A. caviae (0.48 ± 0.24%) than A. veronii (0.21 ± 0.15%). Further, the MIC of PMO was compared in six groups: Group 1: Tetracycline Resistant A. veronii (TRV); Group 2: Tetracycline Resistant A. caviae (TRC); Group 3: Sulfonamide Resistant A. veronii (SRV); Group 4: Sulfonamide Resistant A. caviae (SRC); Group 5: Susceptible A. veronii (SV) and Group 6: Susceptible A. caviae (SC). No significant differences were observed between overall resistant (TRV+ SRV) and susceptible A. veronii (SV). However, in A. caviae, the resistant group had a lower MIC than the susceptible group. Moreover, the MIC was significantly lower for TRC (0.31 ± 0.11%) as compared to SRC (0.46 ± 0.10%). The time of kill of PMO for both the species of Aeromonas was 20-30 min. CONCLUSION: Palmarosa oil exhibited significantly higher activity on A. veronii than A. caviae. The resistant strains of A. caviae were inhibited at a lower concentration than susceptible strains. SIGNIFICANCE AND IMPACT OF THE STUDY: Palmarosa oil could be explored as an alternative antimicrobial agent for mitigating antimicrobial resistance and managing Aeromonas infection in fish and their risks to public health.