Comparing TiO2 photocatalysis and UV-C radiation for inactivation and mutant formation of Salmonella typhimurium TA102.

Abstract

Salmonellosis is one of the most common causes of foodborne bacterial human disease worldwide, and the emergence of multidrug-resistant (MDR) strains of Salmonella enterica serovar Typhimurium (S. typhimurium) was associated to the incidence of invasive salmonellosis. The objective of the present work was to investigate the effects of the TiO2 photocatalysis process in terms of both bacteria inactivation and the emergence of mutants, on S. typhimurium TA102 water suspensions. The TiO2 photocatalysis was compared with a conventional disinfection process such as UV-C radiation. In spite of the faster bacterial inactivation obtained in UV-C disinfection experiments (45, 15, and 10min for total inactivation for initial cell density 109, 108, and 107CFUmL-1, respectively), photocatalytic disinfection (60, 30, and 15min) was more energy efficient because of a lower energy requirement (2-20mWscm-2) compared to the UV-C disinfection process (5-30mWscm-2). During the photocatalytic experiments, the mutation frequency increased up to 1648-fold compared to background level for a 108CFUmL-1 initial bacterial density, and mutants were inactivated after 1-10-min treatment, depending on initial bacterial cell density. In UV-C disinfection experiments, the mutation frequency increased up to 2181-fold for a 108CFUmL-1 initial bacterial cell density, and UV-C doses in the range of 0.5-4.8mWscm-2 were necessary to decrease mutation frequency. In conclusion, both disinfection processes were effective in the inactivation of S. typhimurium cells, and mutants released into the environment can be avoided if cells are effectively inactivated.