Abstract
The presence of nickel could modify bacterial behavior and susceptibility to antimicrobial agents. Adhesion and biofilm formation on orthodontic archwires can be a source of bacterial colonization and possible health hazards. Staphylococcus aureus was subjected to exposure and adaptation to various sub-inhibitory concentrations of nickel. Five strains of bacteria adapted to nickel in concentrations of 62.5–1000 μg/mL were tested for adhesion and biofilm formation on nickel-titanium archwires. Archwires were previously incubated in artificial saliva. Bacteria were incubated with orthodontic wire with stirring for 4 h (adhesion) and 24 h (biofilm formation). The number of adherent bacteria was determined after sonication and cultivation on the Muller-Hinton agar. Disk diffusion method was performed on all bacteria to assess the differences in antimicrobial susceptibility. Bacteria adapted to lower concentrations of nickel adhered better to nickel-titanium than strains adapted to higher concentrations of nickel (p < 0.05). Biofilm formation was highest in strains adapted to 250 and 500 μg/mL of nickel (p < 0.05). The highest biofilm biomass was measured for strains adapted to 250 μg/mL, followed by those adapted to 1000 μg/mL. Bacteria adapted to lower concentrations of nickel demonstrated lower inhibition zone diameters in the disk diffusion method (p < 0.05), indicating increased antimicrobial resistance. In conclusion, bacteria adapted to 250 μg/mL of nickel ions adhered better, demonstrated higher biofilm formation and often had higher antimicrobial resistance than other adapted and non-adapted strains.
Highlights
Nickel can be released to the human body by oral corrosion of nickel-containing dental alloys used for dental instruments, restorations and orthodontic appliances [1].Orthodontic treatment with fixed appliances lasts about 2–2.5 years, and numerous studies have shown corrosion and release of nickel into the oral cavity [2]
S. aureus adapted to 250 μg/mL demonstrated the highest adhesion over the others, while the strain adapted to 1000 μg/mL had the lowest
This research confirmed that corrosion-induced nickel release from orthodontic appliances could modify the behavior of bacteria in the oral cavity depending on the dose of released nickel
Summary
Orthodontic treatment with fixed appliances lasts about 2–2.5 years, and numerous studies have shown corrosion and release of nickel into the oral cavity [2]. The release of nickel from orthodontic appliances is lower in static conditions than under functional stress, but the additional dietary intake of nickel ranging from 130–165 μg per day and the cumulative effect during long-lasting treatment should be considered [6]. Nickel has been shown to have various effects on bacteria In lower concentrations, it is used as a micronutrient, but in higher concentrations can be bacteriostatic [9,10]. It is used as a micronutrient, but in higher concentrations can be bacteriostatic [9,10] This phenomenon is gaining more interest in the bacterial cross-adaptation and resistance to antibiotics field, which is induced by exposure to heavy metals. The mechanisms of adaptation and resistance of bacteria to heavy metal can be achieved by reduced membrane permeability, activation of the efflux pump, inactivation or mutation of gene encoding targets of both antibiotics and metals and by biofilm formation [11,12,13,14]
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