Inactivation kinetics for plasmonic photothermal based eradication of ESKAPE and Candida albicans pathogens

Leading cause of nosocomial infections worldwide i.e., Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter species collectively referred as ESKAPE and Candida albicans that are associated with high morbidity and mortality rates, tends to develop resistance or escape conventional antimicrobial strategies. This study presents, for the first time, a detailed temperature-time kinetic analysis of the plasmonic photothermal technique against the entire spectrum of ESKAPE and C. albicans pathogens, both individually and in complex combinations thereof. Literature reports inactivation kinetics based on isothermal and non-isothermal principles which involve water baths, oil baths, or thermoresistometer, etc. to obtain the desired inactivation. Here, inactivation kinetics of combination of pathogens, ESKAPE and Candida albicans (with initial load of 5 × 10⁷ CFU/mL of each pathogen) using plasmonic photothermal technique (broadband irradiation in the presence triangular silver nanoplates) are investigated in detail. The result showed complete eradication of the pathogens combination within ∼10 min at 74 °C. Further, effective killing/inactivation of individual pathogens was achieved in merely 3-7.5 min (∼48 °C - 60 °C). The obtained inactivation kinetics revealed key aspects of the pathogen like major morphological changes/alterations including the presence of injured or thermotolerant populations, which were evidenced by shoulder, tailing, and sigmoidal patterns in the survival curves. However, broadband irradiation alone and triangular silver nanoplates alone provided non-significant antimicrobial effect even after 15 min of exposure duration. Further, assessment of inactivation mechanism of pathogens on plasmonic photothermal technique demonstrated reactive oxygen species (ROS) generation and cytoplasmic DNA efflux, thereby revealing synergistic effect of temperature elevation and oxidative stress leading to complete killing/inactivation of the pathogens. The study emphasizes the crucial role of temperature-time process parameters of plasmonic photothermal technique to eliminate broad spectrum pathogens of considerably high initial loadings within few minutes (10 min) at considerably lower temperatures which is 74 °C in comparison to the conventional autoclave which requires operating temperature of 121 °C.