Microorganisms - ENVIS Centre

Recently, there has been an increase in the clinical application of low - level laser irradiation (LLLI) in various fields. LLLI may affect a bacterial growth, and in this study we examine the time - dependent effect of LLLI on the rat intestinal flora, particularly on the bacterium Escherichia coli.

Male Wistar rats were treated with a semiconductor laser (SCL) radiation (continuous wave, l = 654 nm, fluence = 1.27 J/cm²) for 5, 10, 20 and 30 min. The animals were decapitated immediately after a single irradiation, and feces from the lower part of the gut were examined for microflora.

After 5 min exposure to SCL, lactose - negative forms of E. coli and Klebsiella pneumoniae were observed, whilst E. coli growth was inhibited completely in 24 h incubated samples from gut feces. A 10 min - treatment with SCL induced a growth of Candida and decreased a growth of lactose - negative E. coli up to 80%, in contrast to Klebsiella whose growth was not affected. In gut microflora of 20 min - irradiated rats, were found single colonies of lactose - negative forms of E. coli and successfully grown Klebsiella, Candida, and several strains of Streptococci that were not seen in feces of control rats. A 30 - min SCL treatment caused a substantial enhancement of Klebsiella, and Candida growth, whereas all forms of E. coli disappeared under these conditions.

They have demonstrated that a single irradiation by coherent red light caused time - dependent changes in the intestinal microflora of healthy rats that might affect host homeostasis and the right balance of immune system kept by gut microbes.