Listeria monocytogenes strains encoding premature stop codons in inlA invade mice and guinea pig fetuses in orally dosed dams

Abstract

Listeria monocytogenes is an important food-borne bacterial pathogen and listeriosis can result in abortions in pregnant women. The bacterium can colonize food-processing environments, where specific molecular subtypes can persist for years. The purpose of this study was to determine the virulence potential of a group of food-processing persistent L. monocytogenes strains encoding a premature stop codon in inlA (encoding internalin A) by using two orally dosed models, pregnant mice and pregnant guinea pigs. A food-processing persistent strain of L. monocytogenes invaded placentas (n558; 10 % positive) and fetuses (3 % positive) of pregnant mice (n59 animals per strain), similar to a genetically manipulated murinized strain, EGD-e InlA m* (n561; 3 and 2 %, respectively). In pregnant guinea pigs (n59 animals per bacterial strain), a maternofetal strain (from a human fetal clinical fatal case) was isolated from 34 % of placenta samples (n550), whereas both food-processing persistent strains were found in 5 % of placenta samples (n536 or 37). One of the food-processing persistent strains, N53-1, was found in up to 8 % of guinea pig fetal liver and brain samples, whereas the maternofetal control was found in 6 % of fetal tissue samples. As the food-processing persistent strains carry a premature stop codon in inlA but are invasive in orally dosed pregnant mice and guinea pigs, we hypothesize that listerial crossing of the placental barrier can occur by a mechanism that is independent of an interaction between Ecadherin and InlA.

Comparative genomics of human and non-human Listeria monocytogenes sequence type 121 strains

“…These findings suggest that inlA -independent invasion pathways for certain tissues or organs may exist. This is supported by the finding that ST121 strains harboring truncated inlA genes are able to cross the placental barrier and infect fetuses in mice and guinea pigs [81]. …”

Listeria monocytogenes Associated with New Zealand Seafood Production and Clinical Cases: Unique Sequence Types, Truncated InlA, and Attenuated Invasiveness

“…These outbreak strains showed attenuated invasion abilities when tested in Caco-2 cell lines, leading to the suggestion that their capacity to cause listeriosis may have been due to inlA-independent properties (e.g., better survival and growth in food and food-associated environments). Holch et al (46) also showed that environmental L. monocytogenes strains harboring inlA-PMSC could cross the placental barrier in a similar way to a strain expressing a full-length inlA in pregnant mice and guinea pigs. These data suggest an inlA-independent pathway for invasion of certain tissues (e.g., the placenta and fetus).…”

Virulence factors and resistance to antimicrobials inListeria monocytogenesserotype 1/2c isolated from food

“…Strains of L. monocytogenes serotype 1/2c are rarely involved in human listeriosis cases according to data reported by ECDC – TESSY, but they may cross the placental barrier (Holch et al . ; Gelbíčová et al . ).…”

“…It is notable that the strains of serotype 1/2c that possess PMSC mutations in inlA gene and attenuated protein forms are still able to cross intestinal and placental barriers and cause human disease (Holch et al . ; Gelbíčová et al . ).…”