Assessment of Streptococcus mutans biofilms on orthodontic adhesives over 7 days.

INTRODUCTION: The purpose of this study was to compare the metabolism of Streptococcus mutans biofilms after 1-7 days of growth on different orthodontic adhesives. METHODS: Specimens of 6 commercial orthodontic adhesives were fabricated in custom-made molds and polymerized using a light-emitting diode light-curing unit. Bioluminescent S mutans (UA159:JM10) biofilms were grown on ultraviolet-sterilized specimens for 1, 3, 5, and 7 days (n = 18 biofilms/d/product) in anaerobic conditions at 37°C. The metabolism of biofilms (relative luminescence unit [RLU]) was measured 0, 2, 4, and 6 minutes after exposure to D-luciferin solution using a microplate reader. A linear mixed-effects model was used to analyze the logarithm of RLU (log RLU). The model included fixed effects of products, days, and minutes. Tukey-Kramer post-hoc tests were then performed on the significant predictors of log RLU (α = 0.05). RESULTS: Days (P <0.0001) and minutes (P <0.0001) were independent predictors of log RLU, but the products were not (P = 0.5869). After adjusting for minutes, the log RLU was analyzed with a post-hoc test, and all differences between days were significant with the exceptions of day 3 from day 5 (P = 0.0731) and day 5 from day 7 (P = 0.8802). After adjusting for day, log RLU was analyzed with a post-hoc test and all differences in minutes were significant. CONCLUSIONS: No significant differences in the metabolism of S mutans biofilms were observed among the 6 orthodontic adhesives. Biofilms that were grown for 3 days demonstrated the highest levels of biofilm metabolism as evidenced by higher mean log RLU values relative to 1, 5, and 7-day growth durations.

Taxis of Pseudomonas putida F1 toward phenylacetic acid is mediated by the energy taxis receptor Aer2.

The phenylacetic acid (PAA) degradation pathway is a widely distributed funneling pathway for the catabolism of aromatic compounds, including the environmental pollutants styrene and ethylbenzene. However, bacterial chemotaxis to PAA has not been studied. The chemotactic strain Pseudomonas putida F1 has the ability to utilize PAA as a sole carbon and energy source. We identified a putative PAA degradation gene cluster (paa) in P. putida F1 and demonstrated that PAA serves as a chemoattractant. The chemotactic response was induced during growth with PAA and was dependent on PAA metabolism. A functional cheA gene was required for the response, indicating that PAA is sensed through the conserved chemotaxis signal transduction system. A P. putida F1 mutant lacking the energy taxis receptor Aer2 was deficient in PAA taxis, indicating that Aer2 is responsible for mediating the response to PAA. The requirement for metabolism and the role of Aer2 in the response indicate that P. putida F1 uses energy taxis to detect PAA. We also revealed that PAA is an attractant for Escherichia coli; however, a mutant lacking a functional Aer energy receptor had a wild-type response to PAA in swim plate assays, suggesting that PAA is detected through a different mechanism in E. coli. The role of Aer2 as an energy taxis receptor provides the potential to sense a broad range of aromatic growth substrates as chemoattractants. Since chemotaxis has been shown to enhance the biodegradation of toxic pollutants, the ability to sense PAA gradients may have implications for the bioremediation of aromatic hydrocarbons that are degraded via the PAA pathway.