Fluorescence Spectra of a Bacterial Population During Different Growth Phases

Biological agents like pathogenic bacteria represent a major threat to the public if spread. Bacteria may replicate in their host and can spread in an unpredictable way. Standoff detection based on laser induced fluorescence may help to mitigate the associated risks. Nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and tryptophan are among others the most important fluorophores in bacteria. Bacteria adapt to their environment and thus the same bacterial species may be composed of different components and relative concentrations of them depending on environmental conditions. Fluorescence spectra of a Bacillus thuringiensis population were compared during different growth phases. Laser pulses with two different excitation wavelengths, 280 nm and 355 nm, were used. For 280 nm excitation the measured spectra show a difference in spectral features between the bacterial population before sporulation and after it was partially sporulated. In comparison a smaller variation in 355 nm excited LIF spectra of a bacterial population during exponential growth and the ageing population is observed.