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Antimicrobial Agents and Chemotherapy, August 2004, p. 2883-2887, Vol. 48, No. 8
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.8.2883-2887.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Effect of Amoxicillin Use on Oral Microbiota in Young Children

Eastman Dental Hospital, University College London Hospitals NHS Trust, London WC1X 8LD,¹ Eastman Dental Institute, University College London, London WC1X 8LD,² Department of Health, London SE1 8UG, United Kingdom³

Received 2 February 2004/ Returned for modification 1 March 2004/ Accepted 14 April 2004

Dental plaque samples from 40 children were screened for the presence of bacteria resistant to amoxicillin. Fifteen children had used amoxicillin and 25 had not used any antibiotic in the 3 months prior to sample collection. All (100%) of the children harbored amoxicillin-resistant oral bacteria. The median percentage of the total cultivable oral microbiota resistant to amoxicillin was 2.4% (range, 0.1 to 14.3%) in children without amoxicillin use and 10.9% (range, 0.8 to 97.3%) in children with amoxicillin use, with the latter value being significantly higher (P < 0.01). A total of 224 amoxicillin-resistant bacteria were isolated and comprised three main genera: Haemophilus spp., Streptococcus spp., and Veillonella spp. The biodiversity of the amoxicillin-resistant microbiota was similar among the isolates from children with and without previous antibiotic use. The amoxicillin MIC at which 90% of the isolates were inhibited for isolates from children who had used amoxicillin in the previous 3 months was higher (64 mg liter^–1) than that obtained for the isolates from subjects who had not used antibiotics (16 mg liter^–1). The majority of the amoxicillin-resistant isolates (65%) were also resistant to at least one of the three antibiotics tested (penicillin, erythromycin, and tetracycline), with resistance to penicillin (51% of isolates) being the most frequently encountered. However, significantly more (P < 0.05) of the amoxicillin-resistant isolates from subjects with previous amoxicillin use were also resistant to erythromycin. This study has demonstrated that a diverse collection of amoxicillin-resistant bacteria is present in the oral cavity and that the number, proportions, MICs, and resistance to erythromycin can significantly increase with amoxicillin use.