The effects of two bile acid derivatives, cholic acid (CA) and deoxycholic acid (DCA) on Staphylococcus aureus (S. aureus) growth were investigated and compared by microcalorimetry coupled with multiple analytical methods. The heat power (HP)-time curves of S. aureus growth affected by CA and DCA were studied by similarity analysis (SA), respectively. Then the quantitative thermo-kinetic parameters obtained from these curves were investigated by the multivariate analysis of variance (MANOVA) and principal component analysis (PCA). By analyzing the two main parameters, growth rate constant k(2) of the second exponential phase and the heat power P(2) of the second highest peak, together with the minimum inhibitory concentration (MIC) values of 10 microg/mL for CA and 20 microg/mL for DCA, it could be concluded that the antibacterial effect of CA was stronger than that of DCA. The existence of alpha-OH at C-7 position of steroid nucleus of bile acid derivatives enhanced the hydrophilicity of compound CA and its inhibitory effect on S. aureus. This study provides a useful method and idea to accurately evaluate the antibacterial effects of bile acid derivatives, which provides some references for screening out new antibacterial agents with high efficacy and low toxicity.
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