Does low-intensity He-Ne laser radiation produce a photobiological growth response in Escherichia coli?

A photobiological study was carried out on the bacterium Escherichia coli in order to determine whether stimulation of growth occurred after irradiation of an inoculum with coherent red light. No enhancement or inhibition of growth was observed for cultures of the bacterium following irradiation of inocula with a Helium-neon laser (continuous wave, lambda = 632.8 nm) at irradiances of 7.7 x 10(15) and 1.8 x 10(16) photons cm-2 s-1 using fluences of 4.5 x 10(-1) and 4.5 J cm-2 at each irradiance. Bacterial growth in irradiated and control cultures was monitored during a growth period of ca 2 h using a viable count technique after inocula in the early exponential phase had been diluted with fresh growth medium. These results do not provide support for the work of Karu et al. (1983, Nuov. Cim. 2D, 1138-1144), and Tiphlova and Karu (1988, Photochem. Photobiol. 48, 467-471), which appear to show substantial enhancement of E. coli growth under these conditions.