Photothermal inactivation of methicillin-resistant Staphylococcus aureus: anti-biofilm mediated by a polypyrrole-carbon nanocomposite.

Widespread resistance to antibiotics amongst pathogens has become a tremendous challenge of high morbidity and mortality rates which increases the needs to exploring novel methods of treatment. An efficient antimicrobial procedure to root out pathogenic bacteria is photothermal therapy. In this study, antimicrobial effects of a polypyrrole-carbon nanocomposite (PPy-C) upon laser irradiation in order to destroy the pathogenic gram-positive bacterium, methicillin-resistant Staphylococcus aureus (MRSA) were assessed. The bacterial cells were incubated with 500, 750 and 1000 μg ml-1 concentrations of PPy-C and irradiated with an 808-nm laser at a power density of 1.0 W cm-2. To indicate the biocompatibility and toxic effect of the nanocomposite without and with laser irradiation, the authors counted the number of CFUs and compared it to an untreated sample. Antibacterial mechanisms of PPy-C were assessed through temperature increment, reactive oxygen species production, and protein and DNA leakages. Photothermal heating assay showed that 26°C temperature increases in the presence of 1000 µg ml-1 PPy-C led to >98% killing of MRSA. Furthermore, 20 min radiation of near-infrared light to PPy-C in different concentrations indicated destruction and reduction in the MRSA biofilm formation. Therefore, PPy-C was introduced as a photothermal absorber with a bactericidal effect in MRSA.