Growth, survival, and resistance of the Legionnaires' disease bacterium

The Legionnaires' disease (LD) bacterium can now be readily cultured on artificial media. Studies were done to define the growth and survival of the LD bacterium in these media and ascertain its susceptibility to disinfecting agents. Growth-curve studies of the Philadelphia 1 strain using Mueller-Hinton broth with ferric pyrophosphate and L-cysteine (Feeley-Gorman broth) showed a lag phase of less than 24 h, a generation time of 3.8 h during the logarithmic phase, a plateau of 2 x 10(7) organisms per millilitre, and continued viability for as long as 110 d. Viability on chocolate agar with 1% hemoglobin and 2% IsoVitaleX added reached 150 d. This strain was susceptible to a variety of commonly recommended hospital and laboratory disinfectants, often in low concentrations. These investigations suggest that prolonged survival may occur in natural as well as artificial milieus and that low concentrations of phenolics, quaternary ammonium compounds, glutaraldehyde, formaldehyde, and hypochlorite could eradicate potential reservoirs for human infection.