Relative Susceptibility of Acid-Fast and Non-Acid-Fast Bacteria to Ultraviolet Light

Mycobacterium tuberculosis strain Erdman, M. bovis (BCG), and M. phlei showed a 1- to 2-log drop in viability after exposure to ultraviolet light compared to a 5-log drop over the same period for Staphylococcus albus, Listeria monocytogenes, Escherichia coli, Pseudomonas aeruginosa, Salmonella enteritidis, and Serratia marcescens. L. monocytogenes showed an initial resistance to ultraviolet inactivation, but later the inactivation rate increased sharply. The significance of these findings with regard to the use of S. marcescens as a test organism for determining the bactericidal efficiency of ultraviolet lamps used to sterilize equipment contaminated with tubercle bacilli is discussed.