Peri-implant inflammation was a frequent finding with and without peri-implant bone loss.

Quaternary ammonium compounds (QACs) are widely used biocides that possess antimicrobial effect against a broad range of microorganisms. These compounds are used for numerous industrial purposes, water treatment, antifungal treatment in horticulture, as well as in pharmaceutical and everyday consumer products as preserving agents, foam boosters, and detergents. Resistance toward QACs is widespread among a diverse range of microorganisms and is facilitated by several mechanisms such as modifications in the membrane composition, expression of stress response and repair systems, or expression of efflux pump genes. Development of resistance in both pathogenic and nonpathogenic bacteria has been related to application in human medicine and the food industry. QACs in cosmetic products will inevitably come into intimate contact with the skin or mucosal linings in the mouth and thus are likely to add to the selection pressure toward more QAC-resistant microorganisms among the skin or mouth flora. There is increasing evidence of coresistance and cross-resistance between QACs and a range of other clinically important antibiotics and disinfectants. Use of QACs may have driven the fixation and spread of certain resistance cassette collectors (class 1 integrons), currently responsible for a major part of antimicrobial resistance in gram-negative bacteria. More indiscriminate use of QACs such as in cosmetic products may drive the selection of further new genetic elements that will aid in the persistence and spread of antimicrobial resistance and thus in limiting our treatment options for microbial infections.

Triclosan is a widely used biocide that is considered as an effective antimicrobial agent against different microorganisms. It is included in many contemporary consumer and personal health-care products, like oral and dermal products, but also in household items, including plastics and textiles. At bactericidal concentrations, triclosan appears to act upon multiple nonspecific targets, causing disruption of bacterial cell wall functions, while at sublethal concentrations, triclosan affects specific targets. During the 1990s, bacterial isolates with reduced susceptibility to triclosan were produced in laboratory experiments by repeated exposure to sublethal concentrations of the agent. Since 2000, a number of studies have verified the occurrence of triclosan resistance amongst dermal, intestinal, and environmental microorganisms, including some of clinical relevance. Of major concern is the possibility that triclosan resistance may contribute to reduced susceptibility to clinically important antimicrobials, due to either cross-resistance or co-resistance mechanisms. Although the number of studies elucidating the association between triclosan resistance and resistance to other antimicrobials in clinical isolates has been limited, recent laboratory studies have confirmed the potential for such a link in Escherichia coli and Salmonella enterica. Thus, widespread use of triclosan may represent a potential public health risk in regard to development of concomitant resistance to clinically important antimicrobials.

DNA has recently been described as a major structural component of the extracellular matrix in biofilms. In streptococci, the competence-stimulating peptide (CSP) cell-to-cell signal is involved in competence for genetic transformation, biofilm formation, and autolysis. Among the genes regulated in response to the CSP are those involved in binding and uptake of extracellular DNA. We show in this study that a functional DNA binding-uptake system is involved in biofilm formation. A comGB mutant of Streptococcus mutans deficient in DNA binding and uptake, but unaffected in signaling, showed reduced biofilm formation. During growth in the presence of DNase I, biofilm was reduced in the wild type to levels similar to those found with the comGB mutant, suggesting that DNA plays an important role in the wild-type biofilm formation. We also showed that growth in the presence of synthetic CSP promoted significant release of DNA, with similar levels in the wild type and in the comGB mutant. The importance of the DNA binding-uptake system in biofilm formation points to possible novel targets to fight infections.Bacteria in natural environments are most often found attached to surfaces, embedded in an extracellular matrix (9). In the biofilm mode, bacteria exhibit increased resistance to antimicrobials and to host defense systems (25). The composition of the extracellular matrix includes polysaccharides and proteins. More recently, extracellular DNA has also been implicated as a major structural component of biofilms (26,31,38).Both gram-positive and gram-negative bacteria communicate through quorum-sensing signals to coordinate population behavior. For Streptococcus pneumoniae, DNA release was recently shown to be activated by the quorum-sensing circuit involved in competence development for natural transformation (27,35). This genetically programmed physiological state is triggered in streptococci by the competence-stimulating signal peptide (CSP). CSP is recognized by the sensor kinase receptor ComD, which autophosphorylates and transfers a phosphoryl group to the ComE response regulator. The gene for the CSP is comC, which in most transformable streptococci is organized in an operon together with comD and comE (15). Phosphorylated ComE activates expression of the comCDE operon and other early competence genes encoding, for instance, the CSP exporter ComAB.Late competence genes, such as those involved in the binding and uptake of extracellular DNA, are regulated by the alternative sigma factor ComX. Expression of ComX is activated by phosphorylated ComE. In S. pneumoniae, more than a hundred genes are regulated by ComX (10, 33).Gram-positive and gram-negative bacteria share several homologous proteins of the DNA binding-uptake machinery, related to type II secretion systems and type IV pili (7). In gram-positive bacteria, comGA and comGB homologues are predicted to encode a traffic NTPase and a polytopic membrane protein, respectively. ComGC shows homology to PilE of Neisseria gonorrhoeae, a major pseudopilin. Three mino...

Individuals with a history of periodontitis were prone to peri-implantitis, peri-implant bone loss ≥ 2.0 mm and overt in the present study. No association was found between smoking and peri-implant disease in the present study population.