Comprehensive antimicrobial susceptibility testing of a large collection of clinical strains of Aggregatibacter actinomycetemcomitans does not identify resistance to amoxicillin.

AIM

The present study aims to determine the susceptibility of Aggregatibacter actinomycetemcomitans to amoxicillin by investigating a large collection of oral strains of diverse geographical origin.

METHODS

Two hundred and fifty-seven A. actinomycetemcomitans strains were serotyped using a multiplex polymerase chain reaction, and minimal inhibitory concentration (MIC) values of amoxicillin were determined using the agar dilution method (range 0.25-8.0 mg/L). The plates were spot-wise inoculated with approximately 10 colony-forming units, incubated in 5% CO at 37 C°, and visually inspected after 24 and 48 hr. A MIC ≤ 2.00 mg/L was categorised as susceptible using EUCAST interpretative criteria for Haemophilus species.

RESULTS

Amoxicillin MIC values varied from 0.25 mg/L to 2.00 mg/L, and all tested strains, including strains previously reported as resistant, were susceptible to amoxicillin. The MIC was 1.00 mg/L and the MIC was 2.00 mg/L.

CONCLUSION

Meticulous investigation of strains including isolates previously reported as resistant could not confirm the emergence of resistance to β-lactams in A. actinomycetemcomitans. Based on the present in vitro results, amoxicillin can be considered a key oral antimicrobial agent for treatment of A. actinomycetemcomitans.