Antimicrobial potential of ulvan against multidrug-resistant oral biofilm-forming bacteria

Abstract Purpose Oral bacteria are considered the most important cause of dental caries occurrence and progression, among which, Staphylococcus lentus is one of the major microorganisms sharing in dental caries process. Aim This article’s objective is to find a new remedy against the most predominant and resistant bacterial strains isolated from dental plaques, using extracted ulvan as a natural biosource. Materials and methods Dental caries cases were surveyed during the year 2024 bacterial isolates were identified by VITEK 2 Compact System and tested for antibiotic resistance. Ulvan was extracted from the collected Ulva crassa , tested for antimicrobial activity, minimum inhibitory concentration, antibiofilm, and anti-inflammatory activity. Then a toothpaste was prepared with the detected antimicrobial extract and tested against the most multidrug-resistant (MDR) and biofilm producing isolate. Results During the survey, it was observed that dental caries was more common among patients under 20 years, with 32 (80%) cases out of a total of 40 cases, during the period from April to September (31 cases). The automated VITEK2 Compact System was used to identify the 82 microbial isolates. From the surveyed 40 cases, the results showed 30 Staphylococcus sp . and 52 non- Staphylococcus sp. Antibiotic resistance of 82 isolates indicated that the most effective antibiotic was ampicillin, while the lowest antibacterial activity was recorded for cefepime. Biofilm formation was assessed for the previously identified MDR isolates (1, 7, 24, 27, 37, 40, 41, 42, 44, 50, 53, and 54), illustrating the highest rates of biofilm formation for isolates no. 1, 53, 44, and 54, with concentrations of 0.62, 0.56, 0.55, and 0.54 μg/ml, respectively. The maximum biofilm formation inhibition, observed at an ulvan concentration of 30 μg/ml, was 39.3% inhibition against tested isolate no. 53, followed by isolate no. 1, which displayed 38.7% inhibition of biofilm formation. Isolate no. 53 was one of the most MDR isolates and was highly suppressed by the examined ulvan. The Staphylococcus sp . identified by the VITEK2 Compact System was confirmed through molecular identification of 16 s rRNA as Mammaliicoccus lentus (as new nomenclature of the previously well-known S. lentus ) with GenBank accession PP657711. Scanning electron microscope showed a noticeable decrease in the quantity of biofilm-forming cells, loss of biofilm structure, and deformation of its 3D architecture. Ulvan exhibited substantial anti-inflammatory action, recording the highest percentage of hemolysis inhibition (53.4%) at a concentration of 70 mg/ml. Conclusion M. lentus was recorded as an important common bacterial contaminant in dental caries, which was investigated as a highly MDR bacterium in the present survey. That could be successfully inhibited by the extracted ulvan, which was explained by the observed antibiofilm activity and improved by anti-inflammatory action of ulvan, as a natural remedy.