Over the last 10-15 yr antibiotic resistance has increased in the oral microflora. The beta-lactam antibiotics, i.e., penicillins and cephalosporins, are the most frequently used antimicrobial agents. Unfortunately, the efficiency of these drugs is increasingly being challenged by the emergence of resistant bacteria, which is mainly due to their production of beta-lactamases. In this paper, mechanisms of antibiotic resistance are reviewed, with emphasis on beta-lactamases. This review also discusses how the presence of beta-lactamases in oral microorganisms may affect the treatment of oral diseases. Dentists can influence the emerging global crisis of antibiotic resistance by carefully evaluating the indications for antibiotic treatment. General guidelines for when and how to use antibiotics in dentistry are reviewed.

The prevalence of ␤-lactamase-producing bacteria in subgingival plaque from patients with refractory periodontitis in Norway was assessed by the chromogenic nitrocefin method. ␤-Lactamase activity was detected in 68% of the patients. Enzyme-producing strains belonged predominantly to the genus Prevotella; others were staphylococci, enteric gram-negative rods, and Bacillus spp.

This study assessed the extent of beta-lactamase-producing bacteria in subgingival plaque samples obtained from 25 patients with refractory marginal periodontitis in the USA. beta-Lactamase-positive isolates were characterized using commercial diagnostic kits and partial sequencing of the 16S rRNA gene. The susceptibilities to different antimicrobial agents were tested and, in addition, the isolates were screened for the presence of extended spectrum beta-lactamases (ESBLs). beta-lactamase-producing bacteria were detected in 18 (72%) patients. The most prominent beta-lactamase-producing organisms belonged to the anaerobic genus Prevotella. Other enzyme-producing anaerobic strains were Fusobacterium nucleatum, Propionibacterium acnes and Peptostreptococcus sp. Facultative bacteria, such as Burkholderia spp., Ralstonia pickettii, Capnocytophaga spp., Bacillus spp., Staphylococcus spp. and Neisseria sp., were also detected among the enzyme-producers. Minimum inhibitory concentrations (MICs) of ampicillin and amoxicillin were in the range 1.5-256 micrograms/ml and 4-256 micrograms/ml, respectively, for the isolates of the Prevotella species. All Prevotella isolates were susceptible to amoxicillin/clavulanate and metronidazole, but they showed variable resistance to tetracyclines. Two of the Prevotella isolates had high MICs of cefotaxime and ceftazidime. ESBL activity was not detected in any of the beta-lactamase-producing isolates by the Etest method. Thus, our study demonstrated a wide variety of beta-lactamase-producing bacteria that may play a role in refractory periodontal disease.

Fifty-three beta-lactamase-producing strains of oral bacteria isolated from patients with refractory periodontitis in Norway and USA were screened for the presence of the bla(TEM), bla(SHV), bla(OXA), bla(ampC), bla(cfxA), and bla(cepA/cblA) genes by the polymerase chain reaction (PCR). The PCR products were characterized by direct sequencing of the amplified DNA. Thirty-four of the 53 enzyme-producing strains (64%) were positive in one of the PCR assays. All beta-lactamase-producing Prevotella and Capnocytophaga spp. were CfxA positive. TEM-type beta-lactamases were identified in one strain each of Escherichia coli and Neisseria sp., and one strain of Citrobacter freundii possessed an AmpC-type beta-lactamase. Screening for gene cassettes and genes known to be associated with integrons did not reveal the presence of integrons in these oral bacteria. Sequence analyses showed that most CfxA positive Prevotella and Capnocytophaga isolates from patients with refractory periodontitis harboured variants of the CfxA2 and CfxA3 enzyme. The present study also showed that many different genetic determinants of beta-lactamase production are found in bacteria isolated from refractory periodontitis, many of which remain to be characterized.

Chromosome-and plasmid-encoded CfxA2 and CfxA3 ␤-lactamases were detected in Capnocytophaga spp. from oral sources in France, Norway, and the United States. Unidentified chromosome-encoded ␤-lactamases were present in Capnocytophaga sputigena. Nucleotide sequence analysis of the CfxA3-encoding plasmid from C. ochracea revealed an unreported insertion sequence (ISCoc1) upstream of the cfxA gene.