Abstract
Insect infection models have been used increasingly to study various pathogenic agents in evaluations of pathogenicity and drug efficacy. In this study, we demonstrated that larvae of the silkworm Bombyx mori are useful for studying Listeria monocytogenes infections in insects. Infection with the L. monocytogenes wild-type strain induced silkworm death. Infection by a listeriolysin O (LLO) deletion mutant also induced silkworm death, but the bacterial numbers in silkworms were lower than those of the wild-type strain. Intracellular growth was observed when the silkworm ovary-derived cell line BmN4 was infected with the wild-type strain. Explosive replication was not observed in BmN4 cells infected with the LLO mutant and the bacterial numbers of the LLO mutant were lower than those of the wild-type strain. Pretreatment with vitamin A did not affect silkworm mortality after bacterial infection, but the efficiency of infecting the hemocytes and BmN4 cells was decreased with vitamin A treatment. Our results indicate that silkworm larvae are a useful insect infection model for L. monocytogenes and that vitamin A has protective effects against bacterial infection in silkworms.
Highlights
Studying host-pathogen interactions and their related factors is of major importance for understanding the molecular mechanisms of human infectious diseases
In order to determine whether the silkworm B. mori can be used as a model system for L. monocytogenes infection, we first examined the infectivity of wild-type L. monocytogenes EGD, an listeriolysin O (LLO) deletion mutant, and an LLO-complemented strain at room temperature
Other significant benefits of this model are that B. mori can be incubated at room temperature (25°C) and the specific virulence factors of L. monocytogenes that are active at this temperature can be found
Summary
Studying host-pathogen interactions and their related factors is of major importance for understanding the molecular mechanisms of human infectious diseases. Model systems are essential for investigating the complex processes of infectious diseases in humans. Listeria monocytogenes is a major food-borne pathogen that causes listeriosis, which is an invasive disease that can lead to meningitis, meningoencephalitis, septicemia, and abortion in its severest form [1]. Listeriosis occurs primarily in pregnant women, newborn infants, and the elderly as well as in immunocompromised patients, with a mortality rate of about 30%. The pathogen has a facultative intracellular life cycle, with the capacity for cellular invasion, intracellular replication and movement from cell to cell without an extracellular phase [2]. Rodents have been established as a useful model for analyzing the systemic phase of L. monocytogenes infections [3], but costs
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