To assess dentistry-based utilization of the 11 antibiotics prescribed by dentists in Norway and its relative contribution to national outpatient consumption and to determine the relationship between numbers of prescriptions and the consumption of these antibiotics. Data on national antibiotic prescriptions by dentists in 2004 and 2005 were used. Consumption of the antibiotics was expressed using WHO defined daily doses (DDDs), DDDs per 1000 inhabitants per day (DIDs) and numbers of prescriptions per 1000 inhabitants (PIDs). Analysis of 268 834 prescriptions issued by 4765 dentists showed that the dentists' prescriptions contributed 8% of the total national consumption of the 11 antibiotics and 13.5%, 2.8% and 1.2% of the national β-lactam penicillins, macrolides and lincosamides and tetracyclines utilization, respectively. The dentists' contributions to the national phenoxymethylpenicillin, spiramycin and metronidazole consumptions were considerably higher (≥13.2%) than for the other prescribed antibiotics (≤8.6%). There was a strong positive correlation between numbers of DDDs and numbers of prescriptions and between DIDs and numbers of PIDs. Reliance of Norwegian dentists on phenoxymethylpenicillin as their first choice suggests a low prevalence of antibiotic resistance among oral bacteria in Norway. Norwegian dentists prefer to prescribe narrow-spectrum antibiotics; their prescribing is conservative and relatively low compared with that of physicians.

To determine the fitness effects of various mobile genetic elements (MGEs) in Enterococcus faecium and Enterococcus faecalis when newly acquired. We also tested the hypothesis that the biological cost of vancomycin resistance plasmids could be mitigated during continuous growth in the laboratory. Different MGEs, including two conjugative transposons (CTns) of the Tn916 family (18 and 33 kb), a pathogenicity island (PAI) of 200 kb and vancomycin-resistance (vanA) plasmids (80–200 kb) of various origins and classes, were transferred into common ancestral E. faecium and E. faecalis strains by conjugation assays and experimentally evolved (vanA plasmids only). Transconjugants were characterized by PFGE, S1 nuclease assays and Southern blotting hybridization analyses. Single specific primer PCR was performed to determine the target sites for the insertion of the CTns. The fitness costs of various MGEs in E. faecium and E. faecalis were estimated in head-to-head competition experiments, and evolved populations were generated in serial transfer assays. The biological cost of a newly acquired PAI and two CTns were both host- and insertion-locus-dependent. Newly acquired vanA plasmids may severely reduce host fitness (25%–27%), but these costs were rapidly mitigated after only 400 generations of continuous growth in the absence of antibiotic selection. Newly acquired MGEs may impose an immediate biological cost in E. faecium. However, as demonstrated for vanA plasmids, the initial costs of MGE carriage may be mitigated during growth and beneficial plasmid–host association can rapidly emerge.

Characterization of extracellular polymeric matrix, and treatment of Fusobacterium nucleatum and Porphyromonas gingivalis biofilms with DNase I and proteinase K

Ampicillin resistance has greatly contributed to the recent dramatic increase of a cluster of human adapted Enterococcus faecium lineages (ST17, ST18 and ST78) in hospital-based infections. Changes in the chromosomal pbp5 gene have been associated with different levels of ampicillin susceptibility, leading to protein variants (designated as PBP5 C-types to keep the nomenclature used in previous works) with diverse degrees of reduction in penicillin affinity. Our goal was to use a comparative genomics approach to evaluate the relationship between the diversity of PBP5 among E. faecium isolates of different phylogenomic groups as well as to assess the pbp5 transferability among isolates of disparate clonal lineages. The analyses of 78 selected E. faecium strains as well as published E. faecium genomes, suggested that the diversity of pbp5 mirrors the phylogenomic diversification of E. faecium. The presence of identical PBP5 C-types as well as similar pbp5 genetic environments in different E. faecium lineages and clones from quite different geographical and environmental origin was also documented and would indicate their horizontal gene transfer among E. faecium populations. This was supported by experimental assays showing transfer of large (≈180-280 kb) chromosomal genetic platforms containing pbp5 alleles, ponA (transglycosilase) and other metabolic and adaptive features, from E. faecium donor isolates to suitable E. faecium recipient strains. Mutation profile analysis of PBP5 from available genomes and strains from this study suggests that the spread of PBP5 C-types might have occurred even in the absence of a significant ampicillin resistance phenotype. In summary, genetic platforms containing pbp5 sequences were stably maintained in particular E. faecium lineages, but were also able to be transferred among E. faecium clones of different origins, emphasizing the growing risk of further spread of ampicillin resistance in this nosocomial pathogen.