Resistance of Listeria monocytogenes in simulated gastrointestinal systems

Abstract:

Abstract:［Objective］Resistance of Listeria monocytogenes was determined through its survival rate and intracellular pH (pHi) after exposed to in vitro digestion models.［Methods］Simulated gastrointestinal systems were prepared according to the major natural components in saliva，gastric juice and contents of the small intestine．Survival of L．monocytogenes was estimated by plate counting and pHi measured via fluorescence ratio imaging microscopy.［Results］L．monocytogenes had a survival rate of over 90% after saliva treatment. Viability was low (less than 0.05%) in gastric juice with pH at or below 3.0 and in the subsequent intestinal fluid. The survival rate started to increase in gastric juice at pH 3.5 and was higher between 11.2%－85.9% for the two tested strains at pH 4.0．The pHi was similar between saliva-treated and untreated bacteria as revealed by fluorescence ratio imaging microscopy. The pHi remained relatively stable at or higher than 7.75 in gastric juice at pH 3.5 and 4.0 or with subsequent introduction of intestinal fluid.［Conclusion］ L．monocytogenes could tolerate gastric juice with pH at or above 3.5 as shown by its good survivability and stable pHi，most probably by maintaining integrity of its membranes.