Chlorine is especially affected by organic matter. Iodine sublimes at high temperatures. Quaternary ammonium compounds have a residual effect, but are not effective against viruses or gram - organisms. Microbial destruction is achieved either by heat or chemicals. The most common method of making foods safe is to use thermal processing to eliminate pathogens and then to use good sanitation practices to prevent them from re-entering the food after thermal processing.
Spores are more resistant than vegetative cells and thus require more heat to kill.
Neither process kills all of the organisms in the food, and non-pathogenic, spoilage organisms can survive to some degree. Since pasteurization does not kill spores, pasteurized products are kept under refrigeration to control the growth of surviving spore formers that grow well at ambient temperature.