Fluorescence emission and excitation spectra were measured over a 7-day period for <i>Bacillus subtilis</i> (<i>Bs</i>), a spore-forming, and <i>Staphylococcus aureus</i> (<i>Sa</i>), a nonspore-forming bacteria subjected to conditions of starvation. Initially, the <i>Bs</i> fluorescence was predominantly due to the amino acid tryptophan. Later, a fluorescence band with an emission peak at 410 nm and excitation peak at 345 nm, from dipicolinic acid, appeared. Dipicolinic acid is produced during spore formation and serves as a spectral signature for detection of spores. The intensity of the 410-nm band continued to increase over the next 3 days. The <i>Sa</i> fluorescence was predominantly from tryptophan and did not change over time. In 6 of the 17 <i>Bs</i> specimens studied, an additional band appeared with a weak emission peak at 460 nm and excitation peaks at 250, 270, and 400 nm. The addition of β-hydroxybutyric acid to the <i>Bs</i> or the <i>Sa</i> cultures resulted in a two-order of magnitude increase in the 460-nm emission. The addition of Fe<sup>2+</sup> quenched the 460 emission, indicating that a source of the 460-nm emission was a siderophore produced by the bacteria. We demonstrate that optical spectroscopy-based instrumentation can detect bacterial spores in real time.
© 2003 Optical Society of America
Alexandra Alimova, Alvin Katz, Howard E. Savage, Mahendra Shah, Glenn Minko, Daniel V. Will, Richard B. Rosen, Steven A. McCormick, and Robert R. Alfano, "Native Fluorescence and Excitation Spectroscopic Changes in Bacillus subtilis and Staphylococcus aureus Bacteria Subjected to Conditions of Starvation," Appl. Opt. 42, 4080-4087 (2003)