The effect of polyoxyethylene stearate (POES) on the growth of mycobacteria in radiometric 7H12 Middlebrook TB medium

Polyoxyethylene stearate (POES) is a non-ionic emulsifying agent. Such agents have been shown to enhance the growth of mycobacteria in vitro. POES (POE(JL)S) has been recommended as an additive to the radiolabelled 7H12 Middlebrook TB media and as such has been shown to enhance growth of mycobacteria in the radiometric BACTEC rapid culture system. We examined the growth enhancing effect of six previously untested POE's (POE(8)S to POE(100)S) whose spreading properties (Hydrophilic-Lipophilic Balances-HLB's) were known. The aim of this study was to determine which POES has the greatest ability to enhance the growth of different mycobacterial species and how the HLB of each POES related to its effect on the growth of each species. We found that POE(50)S produced the greatest enhancement in growth and reduction in the time taken to detect growth for M. tuberculosis and POE(30)S and POE(JL)S for species of mycobacteria other than M. tuberculosis (MOTT). Comparing the effects of POES's to their HLB's (in BACTEC 7H12 media) we suggest four factors which may affect the growth enhancing ability of each POES: 1 its dispersal effect on the bacteria (acting as an emulsifier); 2 it's solubilizer effect on the bacterial cell; 3 the effect the POES on the dispersal of the radiolabelled fatty acid used as a substrate in the media to produce radiolabelled CO2; 4 mycobacteria may metabolise POES.