Antibacterial activity of chitosan from natural resource: <i>Penaeus monodon</i> shell with various concentrations and deacetylation degrees against <i>Lactobacillus acidophilus</i>

Abstract Lactobacillus acidophilus (L. acidophilus) is commonly found in the deep caries. Calcium hydroxide, a standard for direct pulp capping, has drawbacks such as tunnel defects. This study investigates the antibacterial activity of chitosan synthesized from Penaeus monodon (P. monodon) shell at various concentrations and deacetylation degrees (DD) against L. acidophilus. Chitosan synthesized from P. monodon shell as natural resource from Tarakan, Indonesia with DD 81.21% and 92.96% was prepared, each diluted on concentrations of 3%; 1.5%; 0.75%; 0.375%; 0.188%; 0.094%; 0.046%; and 0.023%. Antibacterial activity was examined by dilution method and colony counting on BHI agar. Data were analyzed using Kruskal-Wallis and Mann-Whitney tests. Chitosan DD 81.21% showed zero growth at 0.375% to 3%, while 0.023% to 0.188% performed growth (11.25 to 115 CFU/ml). Significant differences were observed, except for the 0.375% to 3% (p&lt;0.05). Chitosan 92.96% showed zero growth at 0.188% to 3%, while 0.023% to 0.094% performed growth (10.5 to 86.5 CFU/ml). Significant differences were observed, except for the 0.188% to 3% (p&lt;0.05). In conclusion, chitosan DD 81.21% was effective at 0.375% to 3%, while chitosan DD 92.96% exhibited pronounced effectivity at 0.188% to 3%. Increasing concentration and DD of chitosan from P. monodon shell enhances antibacterial activity.