Amoxicillin-metronidazole disk for antimicrobial susceptibility testing of subgingival bacteria.

BACKGROUND

Antibiotics are used in periodontal therapy in selected cases, but therapy is rarely guided by antimicrobial susceptibility testing (AST). Direct AST of the oral microbiota using a combination disk with different antibiotics could provide a new way of AST to guide treatment planning.

METHODS

We performed AST of 46 strains of , , , and , with a combination disk of amoxicillin (AMX) and metronidazole (MET). The AMX-MET was compared to the largest inhibition zone diameter (IZD) obtained with AMX or MET disks, using an ordinary least square linear regression model.

RESULTS

The IZD of the AMX-MET correlated with the AMX for (interception 0.3) and with the MET for (interceptions -1.25). For , the AMX-MET was compared to AMX and MET after 20 and 44 h resulting in a superior correlation after 20 h (interception 0.06 vs 6.61 after 44 h). For , the AMX-MET was compared to MET after 44 h resulting in an inferior correlation (interception 16.65).

CONCLUSION

The IZD of AMX-MET was comparable to that of AMX and MET for important periodontal pathogens, which opens for studies on direct AST of oral samples with a mixed microbiota.

KEY MESSAGE

The amoxicillin-metronidazole disk for antimicrobial susceptibility testing results in comparable inhibition zone diameters to that of AMX and MET for important periodontal pathogens.