Influence of pH on bile sensitivity amongst various strains of Listeria monocytogenes under aerobic and anaerobic conditions

Abstract

Listeria monocytogenes is a dangerous bacterium that causes the food-borne disease listeriosis and accounts for nearly 20 % of food-borne deaths. This organism can survive the body's natural defences within the digestive tract, including acidic conditions and bile. Although the bile response has been analysed, limited information is available concerning the ability of L. monocytogenes to resist bile under anaerobic conditions, especially at acidic pH, which mimics conditions within the duodenum. Additionally, it is not known how the bile response varies between serotypes. In this study, the survival of strains representing six serotypes was analysed under aerobic and anaerobic conditions following exposure to bile. Exposure to bile salts at acidic pH increased toxicity of bile, resulting in a significant reduction in survival for all strains tested. However, following this initial reduction, no significant reduction was observed for an additional 2 h except for strain 10403S (P = 0.002). Anaerobic cultivation increased bile resistance, but a significant increase was only observed in virulent strains when exposed to bile at pH 5.5. Exposure to pH 3.0 prior to bile decreased viability amongst avirulent strains in bile in acidic conditions; oxygen availability did not influence viability. Together, the data suggested that being able to sense and respond to oxygen availability may influence the expression of stress response mechanisms, and this response may correspond to disease outcome. Further research is needed on additional strains to determine how L. monocytogenes senses and responds to oxygen and how this varies between invasive and non-invasive strains.

Oxygen deprivation influences the survival of Listeria monocytogenes in gerbils1

“…As previous studies indicated anaerobiosis increased the ability of L. monocytogenes to resist stressors in vitro (Payne et al, 2013; White et al, 2015), we aimed to conduct an exploratory study to determine whether cultivating L. monocytogenes under anaerobic conditions increased bacterial survival within the GI tract in vivo. Gerbils that were inoculated with a low aerobic or anaerobic dose of F2365 had no significant weight loss following the challenge in comparison to day 0 (Figure 1).…”

“…This bacterium, as well as other foodborne pathogens, is exposed to anaerobic conditions during food processing, storage in vacuum sealed containers, and the infectious pathway (Lungu et al, 2009). Research has previously indicated that L. monocytogenes have an increase in survival in acidic bile under anaerobic conditions in comparison to aerobic environments (White et al, 2015). In addition, virulence has been shown to increase in L. monocytogenes strain Scott A when cultured under oxygen-restricted conditions in a guinea pig model (Bo Andersen et al, 2007).…”

The Listeria monocytogenes Bile Stimulon under Acidic Conditions Is Characterized by Strain-Specific Patterns and the Upregulation of Motility, Cell Wall Modification Functions, and the PrfA Regulon

“…A separate comparative transcriptomic study using six strains representing lineage I and II, grown to late logarithmic phase, identified differences in virulence, cell wall and stress response between the two lineages (Severino et al, 2007 ). Furthermore, strain differences in bile sensitivity have been documented in L. monocytogenes (White et al, 2015 ) and Lactobacillus plantarum , a probiotic and commensal bacterium commonly found in the gastrointestinal tract (Hamon et al, 2011 ), suggesting that strains and clonal groups within bacterial species may show specific adaptation to the gastrointestinal tract that should be explored to develop a better understanding of enteric pathogen transmission. While our comparative genomic analyses suggest that we have identified lineage-, serotype-, and strain-specific genes conserved in L. monocytogenes and other Listeria species, RNA-seq experiments on additional strains representing different L. monocytogenes lineages will be needed to confirm lineage-specific responses to bile exposure.…”

Gut Microbiota and Colonization Resistance against Bacterial Enteric Infection

“…At decreased pH levels, e.g., in the duodenum, bile salts are more acidic and show higher toxicity (250). However, this toxicity seems to be strain dependent (251). The strain responsible for a 2011 outbreak even displayed higher bile resistance at pH 5.5 than at pH 7.0, further indicating that bile susceptibility may be strain dependent (251).…”