Investigation of Staphylococcus aureus inactivation by pulsed UV-light and infrared heating using micro-spectrometry and transmission electron microscopy

Pulsed UV-light and infrared heat treated S. aureus cells were analyzed using transmission electron microscopy to identify the damages caused during the treatment. A five second treatment of S. aureus with pulsed UV-light resulted In complete inactivation of S. aureus even after enrichment. The temperature increase during the pulsed UV-light treatment was 2°C S. aureus was treated using six ceramic infrared lamps with the power of 500 W. A 5 ml of S. aureus cells in phosphate buffer was treated at 700°C lamp temperature for 20 min. The microscopic observation clearly indicated that there was cell wall damage, cytoplasmic membrane shrinkage, cellular content leakage, and mesosome disintegration for both pulsed UV-light and infrared treatments. The structural damage of S. aureus during pulsed UV-light treatment might be caused by the constant disturbances of the intermittent pulses. Temperature increase might be the cause of the cellular damage by infrared heat treatment. FTIR microspectrometry was successfully used to classify the pulsed UV-light and infrared heat treated S. aureus by discriminant analysis. Further investigation on identification of key absorption bands may result in a better assessment of the chemical and structural changes during pulsed UV-light and Infrared heating.