In vitro-antimicrobial activity of essential oils alone and in combination against Salmonella, and its correlation with antibiotics

Due to the dearth of new antibiotics (AB) in the market and the rise in bacterial resistance to ABs, there is need to discover new antimicrobials. Therefore in the present study, we investigated minimum inhibitory concentrations (MIC) of essential oil (EO) Cinnamaldehyde or Citral individually and their combination (1:1 w/w). The broth microdilution method determined the MIC of EO and AB against Salmonella of poultry origin (N=50). These MICs of EOs were correlated with MICs of 12 different ABs by Pearson correlation coefficient. We reported the least MIC (mean ± S.E. in mg/ml) for EO Cinnamaldehyde (2.01 ± 0.13) followed by EO mixture (3.58 ± 0.23) and citral (4.04 ± 0.40). The correlation coefficients between MIC of EO mixture and AB revealed a negative correlation with 5 out of 12 tested ABs. The negative correlation observed with these 5 ABs in the present study indicated that increased resistance to these ABs against Salmonella is associated with increased susceptibility to the EOs and vice versa. From the present study we conclude that EO Cinnamaldehyde and Citral has good anti-Salmonella activity and the combination of these two essential oils (1:1 w/w proportion) resulted in an additive effect against poultry Salmonella.