relA Inactivation Converts Sulfonamides Into Bactericidal Compounds.

Area of Science:

• Microbiology
• Molecular Biology
• Pharmacology

Background:

• Folates are essential for bacterial survival, involved in synthesizing key metabolites.
• Sulfonamides (e.g., sulfamethoxazole) inhibit bacterial folate biosynthesis and are broad-spectrum antimicrobials.
• These drugs are typically bacteriostatic, inhibiting bacterial growth.

Purpose of the Study:

• To investigate the mechanism by which deleting the relA gene alters the activity of sulfamethoxazole.
• To determine if sulfamethoxazole's bactericidal effect is linked to thymine deficiency.
• To explore the potential of targeting RelA for enhanced sulfonamide efficacy.

Main Methods:

• Genetic modification of *Escherichia coli* by deleting the *relA* gene.
• Treatment of bacterial cultures and *E. coli* O157 in mice with sulfamethoxazole.
• Analysis of reactive oxygen species, ferrous ion accumulation, and DNA damage.
• Assessment of bacterial viability and antimicrobial effects.

Main Results:

• Deletion of *relA* converted sulfamethoxazole from a bacteriostat to a bactericide in *E. coli* and other bacteria.
• The bactericidal effect was not due to thymine deficiency.
• Sulfamethoxazole treatment in *E. coli* ∆*relA* led to intracellular accumulation of reactive oxygen species and ferrous ions.
• This accumulation resulted in extensive DNA double-strand breaks, independent of incomplete base excision repair.
• Sulfamethoxazole demonstrated bactericidal activity against *E. coli* O157 ∆*relA* in a mouse model.

Conclusions:

• The study reveals a previously unknown bactericidal mechanism for sulfonamides.
• Targeting RelA can potentiate sulfonamides, converting them into bactericides.
• This finding advances the understanding of sulfonamide action and suggests new strategies for antimicrobial drug development.