Background:  Two strains of Listeria monocytogenes (Lmo), a foodborne pathogen, are reported to able to exist and grow in the murine gall bladder system, tolerating bile salts (BS). The universality of the tolerance was tested in vitro with 100 strains from clinical and food sources.

Methods:  Listeria strains (N=30) were tested in Trypticase Soy Broth with yeast extract (TSBye) plus ox gall (0.625-25%w/v). Growth rates on Trypticase Soy Agar-yeast extract (TSAye) plus 4%w/v ox-gall were estimated from colony diameters measurements.  Cells were stained and observed by light microscopy. Bile salt hydrolase activity (BSH) was detected anaerobically by production of opacity zones and/or chalk-white growth of stabs in deMan-Rogosa-Sharpe agar (MRS) with (0.5 %w/v) Na taurodeoxycholate (TDCNa) or Na glycodeoxycholate (GDCNa). All incubations were at 37°C. The GDCNa responses of 40 clinical and 60 food isolates were compared. 

Results: Lmo strains were able to tolerate at least 18.75%w/v bile in TSBye. Lmo grew half as fast on 5%-oxbile-TSAye as on TSAye tending to form filaments. Lmo formed distinctive chalk-white colonies on TDCNa- and GDCNa-MRS agar. An opacity zone was seen sometimes especially with GDCNa. No BSH activity was observed with the ox-gall or bile salts # 3.  GDCNa-opacity-zones occurred more often with clinical than with food isolates. This may help in screening the pathogenic potential of Lmo strains.

Conclusions:  BS concentrations higher than found in the human biliary system are tolerated by Lmo. Conceivably, at least, a human carrier might disseminate Lmo just like the cook “Typhoid Mary” spread Salmonella typhi.