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Effect of Vitamin A on Listeria monocytogenes Infection in a Silkworm Model

View Article: PubMed Central - PubMed

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.

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Intracellular replication of L. monocytogenes in BmN4 cells.(A)L. monocytogenes replicates intracellularly in BmN4 cells. The silkworm ovary-derived cell line BmN4 was infected with the wild-type strain (WT), LLO deletion mutant (Δhly), and LLO-complemented strain (Δhly::hly) at an MOI of 10. Bacterial invasion and intracellular replication by each strain were measured at 3 h and 24 h after infection. The data represent averages based on triplicate samples from three identical experiments and the error bars represent the standard deviations. Significant differences were accepted at P < 0.05 and they are indicated by asterisks (*). (B) BmN4 cells (red) containing L. monocytogenes strains (green, white arrowheads) were observed by confocal laser scanning microscopy at 3 h and 24 h post inoculation. Scale bar represents 20 μm. Explosive bacterial replication is indicated by open arrowheads. The experiment was replicated three times independently.
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pone.0163747.g002: Intracellular replication of L. monocytogenes in BmN4 cells.(A)L. monocytogenes replicates intracellularly in BmN4 cells. The silkworm ovary-derived cell line BmN4 was infected with the wild-type strain (WT), LLO deletion mutant (Δhly), and LLO-complemented strain (Δhly::hly) at an MOI of 10. Bacterial invasion and intracellular replication by each strain were measured at 3 h and 24 h after infection. The data represent averages based on triplicate samples from three identical experiments and the error bars represent the standard deviations. Significant differences were accepted at P < 0.05 and they are indicated by asterisks (*). (B) BmN4 cells (red) containing L. monocytogenes strains (green, white arrowheads) were observed by confocal laser scanning microscopy at 3 h and 24 h post inoculation. Scale bar represents 20 μm. Explosive bacterial replication is indicated by open arrowheads. The experiment was replicated three times independently.

Mentions: It well known that L. monocytogenes is an intracellular pathogen. To examine the intracellular replication kinetics of L. monocytogenes, we infected the silkworm ovary-derived cell line BmN4 with the wild-type strain, LLO deletion mutant, and LLO-complemented strain at an MOI of 10. We measured the bacterial invasion and intracellular replication of each strain at 3 h and 24 h after infection. The bacterial count of the LLO deletion mutant was significantly lower in BmN4 cells compared with those of the wild-type strain and LLO-complemented strain at 3 h and 24 h post infection (Fig 2A). Intracellular replication by all three strains was observed at 24 h post infection.


Effect of Vitamin A on Listeria monocytogenes Infection in a Silkworm Model
Intracellular replication of L. monocytogenes in BmN4 cells.(A)L. monocytogenes replicates intracellularly in BmN4 cells. The silkworm ovary-derived cell line BmN4 was infected with the wild-type strain (WT), LLO deletion mutant (Δhly), and LLO-complemented strain (Δhly::hly) at an MOI of 10. Bacterial invasion and intracellular replication by each strain were measured at 3 h and 24 h after infection. The data represent averages based on triplicate samples from three identical experiments and the error bars represent the standard deviations. Significant differences were accepted at P < 0.05 and they are indicated by asterisks (*). (B) BmN4 cells (red) containing L. monocytogenes strains (green, white arrowheads) were observed by confocal laser scanning microscopy at 3 h and 24 h post inoculation. Scale bar represents 20 μm. Explosive bacterial replication is indicated by open arrowheads. The experiment was replicated three times independently.
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pone.0163747.g002: Intracellular replication of L. monocytogenes in BmN4 cells.(A)L. monocytogenes replicates intracellularly in BmN4 cells. The silkworm ovary-derived cell line BmN4 was infected with the wild-type strain (WT), LLO deletion mutant (Δhly), and LLO-complemented strain (Δhly::hly) at an MOI of 10. Bacterial invasion and intracellular replication by each strain were measured at 3 h and 24 h after infection. The data represent averages based on triplicate samples from three identical experiments and the error bars represent the standard deviations. Significant differences were accepted at P < 0.05 and they are indicated by asterisks (*). (B) BmN4 cells (red) containing L. monocytogenes strains (green, white arrowheads) were observed by confocal laser scanning microscopy at 3 h and 24 h post inoculation. Scale bar represents 20 μm. Explosive bacterial replication is indicated by open arrowheads. The experiment was replicated three times independently.
Mentions: It well known that L. monocytogenes is an intracellular pathogen. To examine the intracellular replication kinetics of L. monocytogenes, we infected the silkworm ovary-derived cell line BmN4 with the wild-type strain, LLO deletion mutant, and LLO-complemented strain at an MOI of 10. We measured the bacterial invasion and intracellular replication of each strain at 3 h and 24 h after infection. The bacterial count of the LLO deletion mutant was significantly lower in BmN4 cells compared with those of the wild-type strain and LLO-complemented strain at 3 h and 24 h post infection (Fig 2A). Intracellular replication by all three strains was observed at 24 h post infection.

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus