Measuring the Antimicrobial Activity of Lauric Acid against Various Bacteriain Human Gut Microbiota Using a New Method

摘要

Lauric acid (LA) has a broad spectrum of anti-microbiological activities againstenveloped viruses and various bacteria, and might be useful to protect against microbialinfection and control the balance and distribution of bacteria in human gut microbiota. Itis not necessarily more difficult to measure antimicrobial activity the traditional way,but it is, however, more laborious. In the present study, we developed a new method tomeasure the antimicrobial activity of LA in multiple samples with a microplate reader. A“test complex” (TC) was produced consisting of 100 μL of agar medium with LA in the bottomlayer and 300 μL of broth in the top layer in 96-well deep-well microplates. Afterward,analysis of the broth in the top layer showed that the antimicrobial activity was the sameas that of the “control complex,” (CC) which consisted of 100 μL of agar medium in thebottom layer and 300 μL of broth with LA in the top layer. Furthermore, evaluation of theantimicrobial effect of the TC when using a microplate reader was the same as that withthe use of the colony counting method. The colony counting method has confirmed that theantimicrobial activity of LA when bacteria are inoculated into the broth was equivalentbetween CC and TC, and we validated this by correlating the number of bacteria withabsorbance. In addition, the broth itself in TC was transparent enough that the turbidityof broth can be used as an index of the number of bacteria, which enabled the use of amicroplate reader for multiple samples. For human gut microbes, LA was shown to have lowantimicrobial activity against commensal lactic acid bacteria, but high antimicrobialactivity against pathogenic and ,suggesting that LA might modulate intestinal health, as confirmed by the proposedmethod.