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Abstract
Bactericidal efficiency of Au and Ag nanoparticles (NPs) is reported with and without photoactivation by white light. Au and Ag NPs were synthesized with an average size of 14±1.2nm and of 4.6±0.5nm, respectively. The size distribution of the Ag colloid was relatively wide. Less than 4% of these NPs were largely decahedral, which, based on numerical calculations, determined the position of the optical band. In contrast, the Au colloid had a narrow optical band; a concentration of 1.3μg/ml was determined by theoretical and experimental spectra. Ag and Au NPs showed a superficial charge of −35mV and +57mV due to the presence of the citrate ions and cetyltrimethylammonium bromide on their surface, respectively. The effect of the NPs concentration on the viability of Escherichia coli and Staphylococcus aureus strains was investigated. It was found that Ag NPs were more effective against E. coli than Au NPs, whereas Au NPs were more effective against S. aureus than Ag NPs. The induced damage to the bacteria by the NPs was evaluated by AFM. The images show that the bacterial cell wall was changed in shape and in surface roughness, being more noticeable in S. aureus than in E. coli. The bactericidal activity of the photoactivated Ag NPs was almost doubled for both bacteria, whereas for the Au NPs, no bactericidal enhancement was observed for either strain. This can be explained by the high efficiency of Ag NPs to absorb white light and the consequent creation of hot spots that contribute to kill the bacteria.
Highlights
The discovery of penicillin and its use around 1940 made a positive change in the treatment of infectious diseases
A negative superficial charge was assigned to Ag NPs (À35 mV) and a positive charge to Au NPs (þ57 mV), indicating that the nanoparticles are stable in water
We infer that the negative sign is due to the adsorption of layers of citrate ions on the surface of Ag NPs during the synthesis; the positive sign is conferred to the CTAB used in the synthesis of Au NPs
Summary
The discovery of penicillin and its use around 1940 made a positive change in the treatment of infectious diseases. Due to the ability of adaptation of the bacteria and the indiscriminate use of antimicrobials, there are numerous resistant microorganisms and diseases caused by bacteria that do not respond to the use of the most common antibiotics, becoming a problem worldwide[1] especially of nosocomial infections. Staphylococcus aureus is one of the main causes of hospital-acquired infections with high antibiotic resistance, and one out of three people carry S. aureus.[2] This microorganism usually causes pneumonia,[3] endocarditis,[4] and skin and soft tissue infections such as abscesses and cellulitis.[5] Other common bacteria is Escherichia coli, which is mainly a commensal bacterium that colonizes the intestine of most mammals, some strains scitation.org/journal/jap under certain circumstances can be pathogenic producing gastrointestinal diseases such as diarrhea. E. coli has evolved through horizontal transfer of virulence genes that resulted into various pathovars that provide it with the ability to colonize and infect other regions of the human body such as urinary and circulatory systems.[6,7]
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