To evaluate the in vitro antibacterial effects and post-antibiotic effect (PAE) of dequalinium chloride against common pathogens isolated from oral infections in China in recent years.

The minimum inhibitory concentration (MIC) was determined by the standard microbroth or agar (for anaerobes) two-fold dilution method; the minimum bactericidal concentration (MBC) was determined by the broth two-fold dilution method; time-kill curves and PAE were determined by the colony count method.

MICs of dequalinium chloride and commonly used antimicrobial drugs were determined for 274 bacterial strains from 22 hospitals in 19 cities across China. Result showed that, for Gram-positive bacteria, the MIC₅₀ values of dequalinium chloride against Staphylococcus aureus and Streptococcus pyogenes were 1 and 2 mg·L^-1, respectively, with MIC₉₀ values of 2 and 4 mg·L^-1, respectively. For Streptococcus pneumoniae, Enterococcus faecalis, and the viridans group streptococci, the MIC₅₀ values were 8, 4 and 8 mg·L^-1, respectively, while the MIC₉₀ values were 8, and 16 mg·L^-1, respectively. Among Gram-negative bacteria, the MIC₅₀ and MIC₉₀ values of dequalinium chloride against Klebsiella pneumoniae were both 64 mg·L^-1; and >512 mg·L^-1 for MIC₅₀ against Pseudomonas aeruginosa. For 32 strains of anaerobic bacteria, the MIC₅₀ and MIC₉₀ of dequalinium chloride were 16 and 128 mg·L^-1, respectively. Dequalinium chloride showed superior antibacterial activity against genera of Peptostreptococcus and Porphyromonas compared to Prevotella. MBC and time-kill curves showed that dequalinium chloride has a good bactericidal effect on Staphylococcus aureus, Streptococcus pyogenes, and oral streptococci, killing bacteria from an initial count of 1.0×10⁵-1.0×10⁶ CFU·mL^-1 to 0 at 1-4 times MIC concentration within 4-24 h. It also showed good bactericidal effect on Enterococcus faecalis. The time-kill curves indicating a concentration-dependent characteristic of the drug. The PAE of dequalinium chloride against the above four bacterial strains was between 0.5-1 h.

Dequalinium chloride exhibits superior antibacterial activity against Gram-positive bacteria than Gram-negative bacteria and anaerobes, especially against Staphylococcus aureus and Streptococcus pyogenes, warranting further clinical research.