Vitamin D Compounds Are Bactericidal against Streptococcus mutans and Target the Bacitracin-Associated Efflux System

Area of Science:

• Microbiology
• Drug Discovery
• Molecular Biology

Background:

• Vitamin D analogs were identified as potent lytic agents against planktonic *Streptococcus mutans* cultures.
• Previous research indicated vitamin D derivatives possess antibacterial lytic activity, but the underlying mechanisms remain unclear.

Purpose of the Study:

• To investigate the synergistic effects of vitamin D derivatives with antibiotics against *S. mutans*.
• To elucidate the mechanism of action for vitamin D derivative-induced bacterial lysis, focusing on the bacitracin resistance pathway.

Main Methods:

• High-throughput screening of FDA-approved drugs to identify compounds with lytic activity against *S. mutans*.
• Combinatorial approach using the vitamin D derivative doxercalciferol and bacitracin.
• Analysis of *S. mutans* mutants with impaired bacitracin resistance mechanisms (ΔmbrA, ΔmbrD).

Main Results:

• Doxercalciferol demonstrated synergistic lytic activity with bacitracin against *S. mutans*.
• The synergistic effect was amplified in *S. mutans* mutants lacking functional MbrABCD (ABC-type transporter) or RgpABCDEFGHI (Rgp system) bacitracin resistance mechanisms.
• Synergy between doxercalciferol and bacitracin was specific to streptococcal species, despite conserved homologous transporters in other bacteria.

Conclusions:

• Vitamin D derivatives exhibit significant lytic activity against *Streptococcus mutans*.
• The mechanism of action involves a pathway dependent on the MbrABCD bacitracin resistance transporter.
• This study highlights a potential therapeutic strategy combining vitamin D analogs with existing antibiotics for treating *S. mutans* infections.