Time-Resolved Studies of Bioluminescence From Photobacterium Leiognathi and Rapid Antimicrobial Susceptibility Testing on E. Coli Using Tunable Diode Laser Spectroscopy

We demonstrate that tunable diode laser spectroscopy (TDLS) can be used as a reliable, convenient and versatile investigative technique for non-invasive, high-sensitivity and time-resolved studies of the expression of various traits by bacterial strains. We use a 2004 nm vertical cavity surface emitting laser and a 4320 nm mid-infrared quantum cascade laser to show that the bioluminescence and simultaneous CO
₂
emission from Photobacterium leiognathi are correlated. The bioluminescence peaks when the growth rate is maximum. This supports the hypothesis that bioluminescence is a cell density-dependent phenomenon. We also show that TDLS can be used for ultra-rapid antimicrobial susceptibility testing without any need of sample preparation. The mole fraction of CO
₂
emitted during the growth of E. coli was recorded for different standardized doses of ampicillin to show the drastic suppression of growth as the antibiotic dose was increased to the recommended minimum inhibitory drug concentration. Growth suppression was detectable within 2 h, which is much shorter than the time required by conventional methods. We conclude that TDLS is a potent technique for validation and refinement of mathematical models of microbial growth that are necessary to better understand the dynamics of the expression of various traits at specific stages of growth. It is also important for rapid antimicrobial susceptibility testing.