Antimicrobial activity of silver nanoparticles supported on S-layer proteins from Lentilactobacillus kefiri

CARBALLO YE; MINNAARD J; BOLLA PA; SERRADELL MA

Mendoza

Congreso; LVIII Annual Meeting of SAIB; 2022

SAIB

Research on nanoparticles obtained on biological supports is a topic of growing interest in nanoscience. The S-layer is a bidimensional proteinaceous structure that covers the surface of several prokaryotic species. Since isolated S-layer proteins (SLP) can reassemble in solution, we have recently synthesized and characterized silver nanoparticles (AgNP) supported on SLP from L. kefiri (Lk), which showed excellent performance as catalysts in the reduction of a dangerous pollutant such as p-nitrophenol. In this work, we aim to evaluate the antimicrobial activity of AgNP supported on SLP from different Lk strains against Gram-positive and Gram-negative pathogens. To synthesize the AgNP/SLP-Lk systems, different SLP-Lk solutions (1 mg/mL) were mixed with a 0.85 mg/mL AgNO3 solution for 24 hs at 25°C. After that, two different reduction strategies (using H2 or NaBH4, respectively) were applied, and six AgNP/SLP-Lk systems were obtained on three different SLP (Lk5, Lk8, and Lk1). Antimicrobial activity was assessed against Staphylococcus aureus ATCC 6538 and Escherichia coli ATCC 25912. Bacteria were incubated in Luria-Bertani broth at approximately 2x1010 cfu/ml and 4x109 cfu/ml, respectively, in absence or presence of two different concentrations of AgNP/SLP-Lk for 24 hs at 37°C using 96-well plates. Then, a 10 ul volume of each culture was seeded in nutritive agar and incubated at 37°C for 24 hs to evaluate colony growth. Bacteria incubated with each SLP-Lk (without AgNP) were included as controls. A bactericidal effect on both pathogens was observed with the highest concentration of all AgNP/SLP-Lk systems studied. However, at the lowest concentration, the AgNP/SLPs obtained by reduction with NaBH4 were not able to inhibit S. aureus, whereas the bactericidal activity against E. coli was observed for the three AgNP/SLP-Lk systems. To note, none of the SLP-Lk contributed to the bactericidal effect observed at any condition. These results revealed that these nanosystems obtained at eco-friendly conditions could be interesting tools for environmental decontamination.