Listeria monocytogenes is an enteric pathogen that can replicate within bile. Tolerance to bile has been suggested to be related to the pathogenic potential of the bacterium. We analyzed whether bile exerts different types of damage to the cell membrane of the virulent strain EGD-e and the avirulent strain HCC23. The growth and morphology of the serovar 1/2a strain EGD-e and the serovar 4a strain HCC23 were analyzed under both aerobic and anaerobic conditions following exposure to bile salts. Our data indicate that exposure to bile salts significantly impairs the growth of HCC23 as compared to EGD-e. Additionally, scanning electron microscopy and transmission electron microscopy analyses indicate that bile salts alter the cell envelope of EGDe and HCC23 differently. Our results indicate that differences exist in the ability of the virulent strain EGD-e and avirulent strain HCC23 to tolerate bile, suggestingthat bile resistance may be directly related to pathogenicity.