Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2000
Publication Date: N/A
Interpretive Summary: Listeria monocytogenes of serotype 4b has been implicated in most foodborne outbreaks of listeriosis. An estimated 35% of human listeriosis cases result in death. Understanding the molecular features which distinguish virulent strains that infect humans from harmless environmental strains is critical to reducing human illness. A total of 80 isolates from each of the three major epidemics in North America were examined for changes in surface composition. Only clinical strains showed a surface change. This may represent a mechanism of these epidemic-associated strains to evade the immune system. This is the first description of a unique biochemical change in clinical isolates which distinguishes them from environmental strains of L. monocytogenes. Information gained from this study will benefit action agencies, such as FSIS, APHIS, and FDA, to assess risks for animal or human disease caused by L. monocytogenes.
Technical Abstract: Listeria monocytogenes of serotype 4b has been implicated in most foodborne outbreaks of listeriosis. Strains of this serotype express a surface antigen, which is associated with the teichoic acid of the cell wall and is recognized by the serotype 4b-specific monoclonal antibody c74.22. Expression of this surface antigen is stable during repeated passages of the cultures in vitro. Surprisingly, examination of multiple isolates from three different outbreaks of listeriosis revealed that ca. 11 to 29% of the outbreak populations consisted of strains that lacked reactivity with c74.22. The 74.22- negative strains were predominantly of clinical origin. In contrast to their c74.22-positive counterparts, which have galactose and glucose on the N-acetylglucosamine of the teichoic acid, the c74.22- negative strains completely lacked galacatose from the teichoic acid, whereas glucose was present. These strains were also resistant to infection by serotype-specific phage 2671. The data suggest the establishment in epidemic strain populations of mutations, which lead to loss of galactose from the teichoic acid and to phage resistance. This surface antigenic change may represent an immune system evasion strategy on the part of these epidemic-associated strains.