Differential Effects of Ethanol on Permissive versus Nonpermissive Macrophages Infected with Legionella pneumophila

Abstract

The effect of ethanol treatment was studied in terms of effect on permissive versus nonpermissive macrophages for growth of Legionella pneumophila, which is an intracellular bacterium causing pneumonia in immunocompromised patients. It was found that ethanol treatment of permissive macrophages from L. pneumophila-susceptible A/J mice evinced a decrease in replication of the bacteria compared with nontreated infected macrophages. Whereas there was more than a 100-fold increase in Legionella growth over a 48-hr culture period in infected A/J mouse macrophages, treatment of the macrophages with 0.5% ethanol depressed the ability of the macrophages to be infected by Legionella approximately 45%. A lower concentration of ethanol had a lesser effect but still resulted in inhibition of the ability of the cells to replicate Legionella. In contrast to ethanol-induced inhibition of the A/J mouse macrophages to replicate Legionella, macrophages from Legionella-resistant BALB/c mice, which only minimally replicated Legionella (i.e., only a 2-fold increase or less over a 48-hr replicated Legionella (i.e., only a 2-fold increase or less over a 48-hr period), treatment with ethanol resulted in their greater replication of the Legionella. This effect was most marked with the 1.0% concentration of ethanol after 7 days of pretreatment, while the 0.5% and 0.1% concentrations of alcohol caused less enhancement of bacterial growth in the cells, but these concentrations still had a significant enhancement effect. Thus, ethanol had differing effects on growth of the opportunistic intracellular bacterium Legionella in macrophages from permissive versus nonpermissive mice. Studies on the mechanisms involved are in progress.