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Effect of erythromycin on Shigella infection of Caco-2 cells
1Department of Microbiology, School of Medicine, Fujita Health University, Toyoake, Aichi, Japan. yhonma@fujita-hu.ac.jp
Abstract:
Erythromycin (EM), one of the macrolides, shows a dose-dependent effect on Shigella flexneri invasion of Caco-2 cells even at concentrations less than the minimum inhibitory concentration (subMIC). LS13, a strain of S. flexneri 1b, invaded Caco-2 cells in vitro. When the strain was treated with subMIC of EM, the invasion efficiency decreased. The carrier rate of the invasion plasmid containing virulence genes was reduced by EM treatment, as determined by the colony pigmentation test on Congo red agar plates. Presence of the invasion plasmid was found to increase susceptibility of the organisms to EM. The growth of virulent organisms carrying the invasion plasmid was inhibited at 25 microg ml(-1) of EM, whereas the growth of organisms without the plasmid was inhibited at 100 microg ml(-1) of EM. This was supported by the finding that the MIC of EM for a virulent isolate of S. flexneri 2a YSH6000 (6.25 microg ml(-1)) and for the mutant strain del-17 (50 microg ml(-1)), carrying the type III apparatus, impaired plasmid. These findings suggested that EM passed through the type III apparatus and suppressed the growth of invasive organisms selectively. This mechanism may account for the clinical effect of EM on shigellosis.
Insights
Erythromycin (EM) at sub-inhibitory concentrations reduces Shigella flexneri invasion by affecting virulence plasmids. This macrolide antibiotic shows selective growth suppression of invasive bacteria, potentially explaining its clinical efficacy in shigellosis treatment.
Area of Science:
- Microbiology
- Pharmacology
- Cell Biology
Background:
- Shigella flexneri invasion of host cells is a key virulence factor in shigellosis.
- Erythromycin (EM), a macrolide antibiotic, exhibits complex interactions with bacterial pathogens.
- Sub-minimum inhibitory concentrations (subMIC) of antibiotics can have non-lethal effects on bacterial virulence.
Purpose of the Study:
- To investigate the dose-dependent effect of Erythromycin (EM) on Shigella flexneri invasion of Caco-2 cells.
- To determine the impact of EM on the invasion plasmid and virulence of S. flexneri.
- To elucidate the mechanism underlying EM's effect on invasive S. flexneri.
Main Methods:
- Treatment of S. flexneri LS13 with subMIC of EM.
- Assessment of bacterial invasion efficiency in Caco-2 cells.
- Congo red agar plate assay to evaluate invasion plasmid carriage.
- Determination of minimum inhibitory concentrations (MIC) for virulent and mutant strains.
Main Results:
- EM at subMIC significantly decreased the invasion efficiency of S. flexneri in Caco-2 cells.
- EM treatment reduced the carrier rate of the invasion plasmid, which contains virulence genes.
- Bacteria carrying the invasion plasmid were more susceptible to EM, with lower growth inhibition concentrations.
- A mutant strain with an impaired type III secretion apparatus showed increased resistance to EM.
Conclusions:
- Erythromycin selectively suppresses the growth of invasive S. flexneri, potentially via its type III secretion apparatus.
- The reduction in invasion plasmid carriage and increased susceptibility of virulent strains contribute to EM's anti-invasive effect.
- These findings suggest a novel mechanism for Erythromycin's clinical effectiveness in treating shigellosis.