Legionella pneumophila virulence conserved after multiple single-colony passage on agar

Abstract

Multiple passage ofLegionella pneumophila on either supplemented Mueller-Hinton or charcoal yeast extract agar by the conventional batch passing technique results in loss of virulence. In this studyL. pneumophila virulence was maintained after multiple passage on buffered charcoal yeast extract (BCYE α) agar by a single-colony transfer technique. Virulence was determined by assessing the growth ofL. pneumophila for thioglycolate-induced susceptible A/J mouse macrophages in vitro and infectivity for susceptible A/J mice in vivo. Passage of the virulentL. pneumophila, 30 times on BCYE α agar by the single-colony transfer procedure still resulted in virulence, as compared with the nonpassaged parental bacteria, both in vitro and in vivo. Lethality for susceptible, A/J mice by systemic infection was comparable for the 30th colony-passaged bacteria and the parentalL. pneumophila. These results show that theL. pneumophila phenotype associated with intracellular growth in macrophages or infectivity for susceptible mice is stable following passage by the single-colony transfer procedure on BCYE α agar.