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Published on: September 3, 2016
Inhibitory effects of soluble MD-2 and soluble CD14 on bacterial growth
Takahiro Ohnishi1, Masashi Muroi, Ken-ichi Tanamoto
1Division of Microbiology, National Institute of Health Sciences, Setagaya, Tokyo 158-8501, Japan. ohnisi@nihs.go.jp
Abstract:
The effects of the soluble forms of the endotoxin receptor molecules sMD-2 and sCD14 on bacterial growth were studied. When Escherichia coli and Bacillus subtilis were incubated at 37 degrees C for 18 hr with either sMD-2 or sCD14, growth of these bacteria was significantly inhibited as evaluated by viable cell counts and NADPH/NADH activity. A mutant of sCD14 (sCD14d57-64) lacking a region essential for LPS binding did not inhibit the growth of E. coli, whereas this mutant did inhibit the growth of B. subtilis. Addition of excess PG to the bacterial culture reversed the inhibitory effect of sMD-2 on the growth of B. subtilis, but not on the growth of E. coli. Furthermore, when evaluated by ELISA, both sMD-2 and sCD14 bound specifically to PG. Taken together, these results indicate that sMD-2 and sCD14 inhibit the growth of both Gram-positive and Gram-negative bacteria and further suggest that binding to PG and LPS is involved in the inhibitory effect of sMD-2 on Gram-positive bacteria and of sCD14 on Gram-negative bacteria, respectively.
Insights
Soluble endotoxin receptor molecules, soluble MD-2 (sMD-2) and soluble CD14 (sCD14), significantly inhibit the growth of Gram-positive and Gram-negative bacteria. Their binding to peptidoglycan (PG) and lipopolysaccharide (LPS) appears crucial for this antibacterial effect.
Area of Science:
- Microbiology
- Immunology
- Biochemistry
Background:
- Soluble forms of endotoxin receptor molecules, sMD-2 and sCD14, are involved in innate immune responses.
- Understanding their direct effects on bacterial viability is crucial for developing novel antimicrobial strategies.
Purpose of the Study:
- To investigate the direct impact of sMD-2 and sCD14 on the growth of Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria.
- To elucidate the mechanisms underlying the observed effects, focusing on molecular interactions with bacterial components.
Main Methods:
- Bacterial cultures (E. coli, B. subtilis) were incubated with sMD-2 and sCD14.
- Bacterial growth was assessed using viable cell counts and NADPH/NADH activity.
- ELISA was employed to evaluate the binding of sMD-2 and sCD14 to peptidoglycan (PG) and lipopolysaccharide (LPS).
- Mutant sCD14 (sCD14d57-64) lacking LPS-binding region was used to assess specificity.
Main Results:
- Both sMD-2 and sCD14 significantly inhibited the growth of E. coli and B. subtilis.
- A mutant sCD14 lacking LPS-binding capacity inhibited B. subtilis but not E. coli growth.
- Addition of excess PG reversed sMD-2's inhibitory effect on B. subtilis but not E. coli.
- ELISA confirmed specific binding of both sMD-2 and sCD14 to PG.
Conclusions:
- sMD-2 and sCD14 exhibit direct antibacterial activity against both Gram-positive and Gram-negative bacteria.
- The inhibitory effects are mediated through interactions with bacterial cell wall components, specifically PG and LPS.
- These findings suggest potential therapeutic applications for sMD-2 and sCD14 in combating bacterial infections.
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