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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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L. monocytogenes infection of BmN4 cells after pretreatment with vitamin A.(A) Pretreatment with vitamin A inhibited L. monocytogenes infection in BmN4 cells. BmN4 was infected with the wild-type strain at a multiplicity of infection of 10. Bacterial invasion and intracellular replication were measured at 3 h and 24 h after infection in BmN4 cells at the indicated vitamin A concentrations (mg/ml). 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. BmN4 cells were pretreated with (11.25 mg/ml) or without vitamin A. Scale bar represents 20 μm. Explosive bacterial replication is indicated by open arrowheads. Filopodia-like structure are indicated by arrows. The experiment was replicated three times independently.
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pone.0163747.g004: L. monocytogenes infection of BmN4 cells after pretreatment with vitamin A.(A) Pretreatment with vitamin A inhibited L. monocytogenes infection in BmN4 cells. BmN4 was infected with the wild-type strain at a multiplicity of infection of 10. Bacterial invasion and intracellular replication were measured at 3 h and 24 h after infection in BmN4 cells at the indicated vitamin A concentrations (mg/ml). 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. BmN4 cells were pretreated with (11.25 mg/ml) or without vitamin A. Scale bar represents 20 μm. Explosive bacterial replication is indicated by open arrowheads. Filopodia-like structure are indicated by arrows. The experiment was replicated three times independently.

Mentions: To determine the effects of vitamin A on non-hemocyte silkworm cells, we infected BmN4 cells with the wild-type strain at an MOI of 10 and we measured bacterial invasion and intracellular replication at 3 h and 24 h after infection. We found that the number of intracellular bacteria decreased at 3 h and 24 h after infection in a dose-dependent manner (Fig 4A). Pretreatment with vitamin A significantly reduced bacterial invasion at concentrations of 2.25 mg/ml and 11.25 mg/ml.


Effect of Vitamin A on Listeria monocytogenes Infection in a Silkworm Model
L. monocytogenes infection of BmN4 cells after pretreatment with vitamin A.(A) Pretreatment with vitamin A inhibited L. monocytogenes infection in BmN4 cells. BmN4 was infected with the wild-type strain at a multiplicity of infection of 10. Bacterial invasion and intracellular replication were measured at 3 h and 24 h after infection in BmN4 cells at the indicated vitamin A concentrations (mg/ml). 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. BmN4 cells were pretreated with (11.25 mg/ml) or without vitamin A. Scale bar represents 20 μm. Explosive bacterial replication is indicated by open arrowheads. Filopodia-like structure are indicated by arrows. The experiment was replicated three times independently.
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pone.0163747.g004: L. monocytogenes infection of BmN4 cells after pretreatment with vitamin A.(A) Pretreatment with vitamin A inhibited L. monocytogenes infection in BmN4 cells. BmN4 was infected with the wild-type strain at a multiplicity of infection of 10. Bacterial invasion and intracellular replication were measured at 3 h and 24 h after infection in BmN4 cells at the indicated vitamin A concentrations (mg/ml). 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. BmN4 cells were pretreated with (11.25 mg/ml) or without vitamin A. Scale bar represents 20 μm. Explosive bacterial replication is indicated by open arrowheads. Filopodia-like structure are indicated by arrows. The experiment was replicated three times independently.
Mentions: To determine the effects of vitamin A on non-hemocyte silkworm cells, we infected BmN4 cells with the wild-type strain at an MOI of 10 and we measured bacterial invasion and intracellular replication at 3 h and 24 h after infection. We found that the number of intracellular bacteria decreased at 3 h and 24 h after infection in a dose-dependent manner (Fig 4A). Pretreatment with vitamin A significantly reduced bacterial invasion at concentrations of 2.25 mg/ml and 11.25 mg/ml.

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