Acinetobacter baumannii is an opportunistic pathogen that is reported as a major cause of nosocomial infections. The aim of this study was to investigate the biofilm formation by A. baumannii clinical and soil isolates, to display their susceptibility to 11 antibiotics and to study a possible relationship between formation of biofilm and multidrug resistance. During 8 months period, from June 2016 to January 2017, a total of 52 clinical and 22 soil isolates of A. baumannii were collected and identified through conventional phenotypic, chromo agar, biochemical tests, API 20E system, and confirmed genotypically by PCR for blaOXA-51-like gene. Antibiotic susceptibility of isolates was determined by standard disk diffusion method according to Clinical and Laboratory Standard Institute. The biofilm formation was studied using Congo red agar, test tube, and microtiter plate methods. The clinical isolates were 100% resistance to ciprofloxacin, ceftazidime, piperacillin, 96.15% to gentamicin, 96.15% to imipenem, 92.31% to meropenem, and 78.85% to amikacin. The soil A. baumannii isolates were 100% sensitive to imipenem, meropenem, and gentamicin, and 90.1% to ciprofloxacin. All A. baumannii isolates (clinical and soil) were susceptible to polymyxin B. The percentage of biofilm formation in Congo red agar, test tube, and microtiter plate assays was 10.81%, 63.51%, and 86.48%, respectively. More robust biofilm former population was mainly among non-MDR isolates. Isolates with a higher level of resistance tended to form weaker biofilms. The soil isolates exhibited less resistance to antibiotics than clinical isolates. However, the soil isolates produce stronger biofilms than clinical isolates.

(1) Background: This study compares the antibacterial effect of coated and impregnated flexible dentures with magnesium oxide nanoparticles (MgONPs) against Streptococcus mutans. (2) Methods: the study used flexible denture material discs. The experimental groups were uncoated dics (control), 5% MgONPs coated discs (coated), and 5% MgONPs impregnated discs (impregnated). The homogenous distribution of MgONPs within the matrix was determined using scanning electron microscopy (SEM), and surface roughness and modulus elasticity were also measured. The antibacterial efficacy was tested against Streptococcus mutans in suspension and biofilm. The adhesion of microorganisms was assessed using an adherence assay test, optical light microscopy, and turbidity test. (3) Results: The nanoparticles were successfully coated or impregnated on the substrate and caused a significant increase in roughness. The effect of 5% MgONPs was significant (p < 0.05). The flexible denture samples whether coated or impregnated with 5% MgONPs effectively inhibited the growth of microorganisms. The Streptococcus mutans growth was 2.5 folds higher in control compared to coated samples, while Streptococcus mutans growth was 1.5 folds higher in control compared to impregnated samples. Furthermore, this study confirmed there was a homogenous distribution of MgONPs for both coated and impregnated groups. (4) Conclusions: It was found that addition of 5% MgONPs can prevent the attachment of Streptococcusn mutans to flexible removable denture material. Additionally, the antibacterial effect was higher in the coated-samples compared to impregnated-samples.

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(1) Background: The aim of this research was to investigate the antibacterial activity of dissolved silver from silver-coated titanium implants against Streptococcus mutans. (2) Methodology: Silver-coated titanium implant discs were immersed in 1.8 mL of brain heart infusion broth (BHIB) and incubated for 24 h in order to release the silver ions into the broth. The coating quality was confirmed via EDS, and the dissolved silver was measured via inductively coupled plasma mass spectrometry (ICP-MS). The experimental design used unconditioned broth (control) and broth conditioned with silver released from silver-coated titanium implants (n = 6). Regarding the antibacterial activity, isolated Streptococcus mutans was used. A turbidity test and lactate production test were performed to determine the effect of dissolved silver on bacterial growth in a suspension and biofilm formation. (3) Result: The results showed that the coating was successfully applied on the substrate. There was around 0.3 mg/L of silver released into the BHIB, and the turbidity of the control group was significantly higher than the treatment, with measured absorbance values of 1.4 and 0.8, respectively, indicating that the dissolved silver ions from the silver-coated titanium discs exhibited some degree of antibacterial activity by preventing the growth of Streptococcus mutans. However, the results of the antibiofilm activity test did not show any significant difference between the groups. (4) Conclusion: The dissolved silver from silver-coated titanium implants has an antibacterial activity but not a significant antimicrobial activity, indicating that the dissolved silver from silver-coated titanium abutments can significantly reduce the incidence of peri-implant mucositis.

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