Intracellular growth of Legionella pneumophila serogroup 1 monoclonal antibody type 2 positive and negative bacteria.

Epidemiological evidence suggests that monoclonal antibody type 2 positive (MAB 2+) Legionella pneumophila serogroup 1 (LP1) more often causes disease than do MAB 2- isolates, and there is evidence that MAB 2- LP1 grow less well in cells than do MAB 2+ bacteria. We tested the intracellular growth rates of ten randomly selected MAB 2- LP1 isolates, by using guinea-pig alveolar macrophages, and human monocyte-derived macrophages. Save a low virulence control, all ten MAB 2- isolates grew as well in cells as a virulent MAB 2+ isolate. Heterogeneity of MAB 2- LP1 growth in cells exists, making poor intracellular growth an unlikely explanation for why MAB 2+ LP1 appear to cause disease more often.