Environmental factors affecting the survival and pathogenicity of Legionella pneumophila
The thermotolerance of Legionella pneumophila was compared with that of other Legionella spp. All showed a similar survival at the temperature tested except L. micdadei which did not survive so well. Isolation media and pretreatment methods developed to isolate legionellae from water were compared using laboratory prepared and natural water samples. A buffered charcoal yeast extract medium containing glycine and antibiotics inoculated with water concentrated by membrane filtration and acid or heat treated provided the best means of isolation. Legionellae isolated during this survey were then used for further studies. Legionella pneumophila serogroup 1 was isolated from aerosols produced by a shower confirming epidemiological evidence of the role showers play in dissemination of the organism. Strains of L. pneumophila sg.1 more commonly associated with disease survived longer in aerosols and were more hydrophobic than strains with little or no disease association. The effect temperature, pH and redox had on aerosol survival, hydrophobicity and physiology of L. pneumophila sg.1. was studied with cells grown in continuous culture. Redox and pH had little affect other than to limit growth. Temperature has the most marked affect. Cells were more hydrophobic when grown at ≤30°C, were surrounded by a polymeric material and survived longer in aerosols than those grown at > 30°C. At ≤25°C cells were often flagellated or fimbriated with large numbers of cells being flagellated if the culture was allowed to move into the stationary phase of growth. Cells grown at 40°C were longer, were not flagellated or fimbriated and had little or no polymeric material adhering. More monoclonal pitopes were expressed in cells grown at 40°C than those grown at 25°C. Cells grown at 25°C had the aerosol and hydrophobic characteristics found for the more virulent strains of L. pneumophila serogroup 1.