Abstract The rice husk, agro-industrial residue, stands out for having silica, the main oxide former of the bioactive glass. To avoid contamination in this biomaterial, substances with bactericidal properties, like silver can be incorporated. Thus, the objective of this work is the synthesis of silver nanoparticles to functionalize a bioactive glass synthesized from rice husk ash (BRHA). The bioglass was prepared by the sol-gel method from the rice husk ash as a silica source. Silver nanoparticles were synthesized from thyme extract with AgNO3 and their formation was verified by UV-vis spectroscopy. The glass powder was added to this solution and its structure was evaluated by SEM-EDS, ATR-FTIR, and microbiology. The bioglass powder appeared in the form of porous agglomerates and the addition of silver altered its superficial roughness by deposition. The chemical bonds of the glass network related to bioactivity were maintained after the incorporation of the nanoparticles. Microbiological analysis by the agar diffusion test confirmed the inhibitory action of the nanoparticles for P. aeruginosa and S. aureus. Therefore, the developed material presented great potential for biomedical applications.

RESUMOA evolução de certos microrganismos permite sua rápida adaptação aos ambientes em constante mudança, desenvolvendo assim, tolerância ou resistência ao aumento de determinados estresses. O uso de compostos bioativos provenientes da flora nativa tem sido apontado como uma possível solução para os problemas de controle da resistência e proliferação bacteriana. Este trabalho visou verificar a adaptação e adaptação cruzada de L. monocytogenes, frente aos compostos fenólicos eugenol e carvacrol. A concentração mínima inibitória (CMI) dos compostos fenólicos foi determinada pela técnica de microdiluição em placas de 96 cavidades, em caldo TSB + 0,5% de Tween 80. As concentrações finais (%) obtidas foram: 0,06; 0,12; 0,24; 0,49; 0,98; 1,95; 3,9; 6,25; 12,5; 25; 50. A suspensão bacteriana padronizada foi inoculada nas cavidades das placas, as quais foram incubadas a 37°C por 24 horas com posterior leitura da absorbância a 620 nm e determinação da CMI. A adaptação das células de L. monocytogenes ao eugenol e carvacrol foi realizada com o cultivo das células em TSB + 0,06% de eugenol ou carvacrol à 37°C por 2 horas. A cultura foi então centrifugada e as células ressuspendidas e padronizadas em TSB. A seguir, realizou-se novamente a técnica de microdiluição em caldo. Os resultados obtidos demonstraram que L. monocytogenes apresentou adaptação e adaptação cruzada frente ao carvacrol e eugenol. A CMI do eugenol e carvacrol foi de 24%. A pré-exposição de L. monocutogenes a concentração sub-letal de 0,06% de carvacrol ou de eugenol aumentou sua resistência. A pré-exposição ao carvacrol promoveu a adaptação de L.monocytogenes a ele aumentando a CMI para 12,5%. Já para o eugenol a CMI passou para 25%. Quando submetidas à concentração sub-letal de eugenol, este promoveu a adaptação das células tanto ao carvacrol quanto ao eugenol, sendo a CMI de 12,5%. Os resultados obtidos demonstraram que L. monocytogenes apresentou adaptação e adaptação cruzada ao carvacrol e eugenol. O presente trabalho sugere estudos futuros ainda mais abrangentes quanto à potencialidade antimicrobiana destes compostos.

ABSTRACTSome microorganisms have evolved and therefore are able to rapidly adapt themselves to a constantly changing environment, thus developing tolerance or resistance to the increase of some specific stresses. The use of bioactive compounds from the native vegetation has been pointed out as a possible solution to the problems of control of bacterial resistance and proliferation. This work aimed to check the adaptation and cross adaptation of L. monocytogenes, towards the phenolic compounds eugenol and carvacrol. The minimum inhibitory concentration (MIC) of the phenolic compounds was determined by the microdilution technic in plates of 96 cavities, in CALDO TSB + 0,5% of Tween 80. The final concentrations (%) obtained were: 0,06; 0,12; 0,24; 0,49; 0,98; 1,95; 3,9; 6,25; 12,5; 25; 50.The patronized bacterial suspension was inoculated into the captivities of the plates, and incubated at 37°C for 24 hours with posterior reading of the absorbance at 620 nm and determination of the MIC. The adaptation of the cells of L. monocytogenes to the eugenol and carvacrol was made through the cultivation of the cells in TSB + 0,06% of eugenol or carvacrol at 37°C for 2 hours. The sample was then centrifuged and the cells were re-suspended and patronized in TSB. After that, the microdilution technic was performed one more time. The obtained results revealed that the L. monocytogenespresented adaptation and cross adaptation to the eugenol and carvacrol. The eugenol and carvacrol CMI was at 24%. The pre-exposition of L. monocytogenes to sub-lethal doses of 0,06% of eugenol or carvacrol enhanced its resistance. The pre-exposition to carvacrol promoted the adaptation of L. monocytogenes to it thus increasingthe MIC to 12,5%. To the eugenol the CMI got to 25%. When submitted to sub-lethal concentrations of eugenol, the latterpromoted the adaptation of the cells to carvacrol and eugenol, bringing the CMI to 12,5%. The obtained results showed that theL. monocytogenespresented adaptation and cross adaptation to the eugenol and carvacrol. The current work suggests future studies even broader regarding the antimicrobial potentialityof these compounds.