Subminimal inhibitory concentrations of antibiotics have been shown to induce bacterial biofilm formation. Few studies have investigated antibiotic-induced biofilm formation in Staphylococcus aureus, an important human pathogen. Our goal was to measure S. aureus biofilm formation in the presence of low levels of β-lactam antibiotics. Fifteen phylogenetically diverse methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) strains were employed. Methicillin, ampicillin, amoxicillin, and cloxacillin were added to cultures at concentrations ranging from 0× to 1× MIC. Biofilm formation was measured in 96-well microtiter plates using a crystal violet binding assay. Autoaggregation was measured using a visual test tube settling assay. Extracellular DNA was quantitated using agarose gel electrophoresis. All four antibiotics induced biofilm formation in some strains. The amount of biofilm induction was as high as 10-fold and was inversely proportional to the amount of biofilm produced by the strain in the absence of antibiotics. MRSA strains of lineages USA300, USA400, and USA500 exhibited the highest levels of methicillin-induced biofilm induction. Biofilm formation induced by low-level methicillin was inhibited by DNase. Low-level methicillin also induced DNase-sensitive autoaggregation and extracellular DNA release. The biofilm induction phenotype was absent in a strain deficient in autolysin (atl). Our findings demonstrate that subminimal inhibitory concentrations of β-lactam antibiotics significantly induce autolysin-dependent extracellular DNA release and biofilm formation in some strains of S. aureus.

Background. An expert panel convened by the American Dental Association Council on Scientific Affairs and the Center for Evidence-Based Dentistry conducted a systematic review and formulated clinical recommendations for the urgent management of symptomatic irreversible pulpitis with or without symptomatic apical periodontitis, pulp necrosis and symptomatic apical periodontitis, or pulp necrosis and localized acute apical abscess using antibiotics, either alone or as adjuncts to definitive, conservative dental treatment (DCDT) in immunocompetent adults. Types of Studies Reviewed. The authors conducted a search of the literature in MEDLINE, Embase, the Cochrane Library, and the Cumulative Index to Nursing and Allied Health Literature to retrieve evidence on benefits and harms associated with antibiotic use. The authors used the Grading of Recommendations Assessment, Development and Evaluation approach to assess the certainty in the evidence and the Evidence-to-Decision framework. Results. The panel formulated 5 clinical recommendations and 2 good practice statements, each specific to the target conditions, for settings in which DCDT is and is not immediately available. With likely negligible benefits and potentially large harms, the panel recommended against using antibiotics in most clinical scenarios, irrespective of DCDT availability. They recommended antibiotics in patients with systemic involvement (for example, malaise or fever) due to the dental conditions or when the risk of experiencing progression to systemic involvement is high. Conclusion and Practical Implications. Evidence suggests that antibiotics for the target conditions may provide negligible benefits and probably contribute to large harms. The expert panel suggests that antibiotics for target conditions be used only when systemic involvement is present and that immediate DCDT should be prioritized in all cases.

Aggregatibacter actinomycetemcomitans a causative agent of periodontal disease in humans, forms biofilm on biotic and abiotic surfaces. A. actinomycetemcomitans biofilm is heterogeneous in nature and is composed of proteins, extracellular DNA and exopolysaccharide. To explore the role played by the exopolysaccharide in the colonization and disease progression, we employed genetic reduction approach using our rat model of A. actinomycetemcomitans-induced periodontitis. To this end, a genetically modified strain of A. actinomycetemcomitans lacking the pga operon was compared with the wild-type strain in the rat infection model. The parent and mutant strains were primarily evaluated for bone resorption and disease. Our study showed that colonization, bone resorption/disease and antibody response were all elevated in the wild-type fed rats. The bone resorption/disease caused by the pga mutant strain, lacking the exopolysaccharide, was significantly less (P < 0.05) than the bone resorption/disease caused by the wild-type strain. Further analysis of the expression levels of selected virulence genes through RT-PCR showed that the decrease in colonization, bone resorption and antibody titer in the absence of the exopolysaccharide might be due to attenuated levels of colonization genes, flp-1, apiA and aae in the mutant strain. This study demonstrates that the effect exerted by the exopolysaccharide in A. actinomycetemcomitans-induced bone resorption has hitherto not been recognized and underscores the role played by the exopolysaccharide in A. actinomycetemcomitans-induced disease.

Background. Patients with pulpal and periapical conditions often seek treatment for pain, intraoral swelling, or both. Even when definitive, conservative dental treatment (DCDT) is an option, antibiotics are often prescribed. The purpose of this review was to summarize available evidence regarding the effect of antibiotics, either alone or as adjuncts to DCDT, to treat immunocompetent adults with pulpal and periapical conditions, as well as additional population-level harms associated with antibiotic use. Type of Studies Reviewed. The authors updated 2 preexisting systematic reviews to identify newly published randomized controlled trials. They also searched for systematic reviews to inform additional harm outcomes. They conducted searches in MEDLINE, Embase, the Cochrane Library, and the Cumulative Index to Nursing and Allied Health Literature. Pairs of reviewers independently conducted study selection, data extraction, and assessment of risk of bias and certainty in the evidence using the Grading of Recommendations Assessment, Development, and Evaluation approach. Results. The authors found no new trials via the update of the preexisting reviews. Ultimately, 3 trials and 8 additional reports proved eligible for this review. Trial estimates for all outcomes suggested both a benefit and harm over 7 days (very low to low certainty evidence). The magnitude of additional harms related to antibiotic use for any condition were potentially large (very low to moderate certainty evidence). Conclusions and Practical Implications. Evidence for antibiotics, either alone or as adjuncts to DCDT, showed both a benefit and a harm for outcomes of pain and intraoral swelling and a large potential magnitude of effect in regard to additional harm outcomes. The impact of dental antibiotic prescribing requires further research.

The oral pathogen Aggregatibacter actinomycetemcomitans uses pga gene locus for the production of an exopolysaccharide made up of a linear homopolymer of β-1,6-N-acetyl-d-glucosamine (PGA). An enzyme encoded by the pgaB of the pga operon in A. actinomycetemcomitans is a de-N-acetylase, which is used to alter the PGA. The full length enzyme (AaPgaB) and the N-terminal catalytic domain (residues 25-290, AaPgaBN) from A. actinomycetemcomitans were cloned, expressed and purified. The enzymatic activities of the AaPgaB enzymes were determined using 7-acetoxycoumarin-3-carboxylic acid as the substrate. The AaPgaB enzymes displayed significantly lower de-N-acetylase activity compared with the activity of the deacetylase PdaA from Bacillus subtilis, a member of the CE4 family of enzymes. To delineate the differences in the activity and the active site architecture, the structure of AaPgaBN was determined. The AaPgaBN structure has two metal ions in the active site instead of one found in other CE4 enzymes. Based on the crystal structure comparisons among the various CE4 enzymes, two residues, Q51 and R271, were identified in AaPgaB, which could potentially affect the enzyme activity. Of the two mutants generated, Q51E and R271K, the variant Q51E showed enhanced activity compared with AaPgaB, validating the requirement that an activating aspartate residue in the active site is essential for higher activity. In summary, our study provides the first structural evidence for a di-nuclear metal site at the active site of a member of the CE4 family of enzymes, evidence that AaPgaBN is catalytically active and that mutant Q51E exhibits higher de-N-acetylase activity.