ANTIMICROBIAL EVALUATION OF ZIRCONIUM DIOXIDE NANOPARTICLES ASSOCIATED WITH SILVER AGAINST Escherichia coli BIOFILM

Escherichia coli is a Gram-negative bacillus commonly found in humans microbiota that, under certain conditions, can cause blood and urinary tract infections. Some resistant isolates of these bacteria are able to form biofilm in medical devices and, thus, trigger several concerns in hospital settings. In addition, the majority of hospitalized patients (about 65%) present nosocomial infection, which is directly related to the presence of microbial biofilms, including E. coli. Therefore, it is necessary to seek new strategies to reduce the occurrence of these risk factors. The zirconium dioxide (ZrO2) is a ceramic material with properties, such as resistance to corrosion and mechanics forces, and has emerged as an interesting option in coating materials to inhibit the proliferation of pathogenic microorganisms. Thus, in the present study, we evaluated the antimicrobial activity of ZrO2 nanoparticles in association with different concentrations of silver (Ag) against E. coli biofilm. For this, we evaluated two concentrations of ZrO2: silver 1% (ZAg1) and silver 10% (ZAg10). E. coli strain (ATCC 25992) was cultivated in the Mueller Hinton broth (MH) with depletion method. For the growth kinetic assay, E. coli was challenged with four concentrations of nanoparticles (2; 1; 0.5; 0.25 mg/ml) at four experimental time points: 0, 2, 4 and 6 hours. The capacity of biofilm formation was determined by Congo red agar medium, that is a sensitive, qualitative and specific method for this analysis. For each time, violet crystal assay was performed to quantify the bacterial biomass produced against the nanoparticles. In addition, we submitted the samples to Scanning Electron Microscopy (SEM). Our results showed that ZrO2 associated with 1% silver (ZAg1) induced 77% of E. coli biomass inhibition and, when associated with 10% silver (ZAg10), induced 47% biomass inhibition (Non-paired T statistical test, with value of p < 0,05), both in the concentration of 2 mg/ml. Scanning Electron Microscopy analyses showed that ZAg1 nanoparticles, at the concentration of 2 mg/ml, showed rupture and deformity of the bacteria. Thus, our results suggest that this material has potential for use as a coating of hospital, dental and catheter materials, reducing and preventing contaminations caused by Escherichia coli and promoting improvement and reduction of infections in patients.