Spores chemical killing

Robert Koch, in Germany in 1881, did scientific laboratory tests on 70 different chemicals, at different concentrations and in different solvents, to assess thek abiUty to kill spores of anthrax bacteria (7). Refinement of the testing methods were made in 1897, 1903, and 1908 (8). They continued to be improved, standardized, and pubUshed under the auspices of organizations like the Association of Official Analytical Chemists (AOAC) (now called AO AC International). 

Death kinetics are obviously important in chemical or thermal sterilization. The spores formed by some bacteria are the hardest to kill. Problem 12.3 gives data for a representative case. 

Disinfectants are strong chemical agents that inhibit or kill microorganisms (Table 50-1). Antiseptics are disinfecting agents with sufficiently low toxicity for host cells that they can be used directly on skin, mucous membranes, or wounds. Sterilants kill both vegetative cells and spores when applied to materials for appropriate times and temperatures. Some of the terms used in this context are defined in Table 50-2. 

The effectiveness of a disinfectant also depends upon the age of the microorganism. For example, young bacteria can easily be killed, while old bacteria are resistant. As the bacterium ages, a polysaccharide sheath is developed around the cell wall this contributes to the resistance against disinfectants. For example, when using 2.0 mg/L of applied chlorine dosage, for bacterial cultures of about 10 days old, it takes 30 min of contact time to produce the same reduction as for young cultures of about one day old dosed with one minute of contact time. In the extreme case are the bacterial spores they are, indeed, very resistant and many of the chemical disinfectants normally nsed have little or no effect on them. 

UV can cause permanent inactivation of virus, bacteria, spores, fungi and other pathogens. UV irradiation disinfection requires no additional chemicals. Unlike chlorination disinfection, it does not produce odor it is usually deemed as the best choice with very low or no DBFs and no residual toxicity. In addition, it is able to kill some chlorine-resistant pathogens such as Cryptosporidium and Giardia. Compared with other disinfection alternatives, UV is a cost-effective, clean, and simple approach. UV disinfection system does not require the transportation, storage, and handling of regulated chemicals such as chlorine. 

The goal of sterilization is to kill (or physically remove) 100% of the living microorganisms and their various resistant reproductive spores (mold conidiospores, yeast ascospores, bacterial endospores) as well. This is different from sanitation, which is a production concept, whereby the total cell count is reduced to an acceptably low number (likely zero). Sterilization of laboratory media and equipment may utilize exposure to conditions of high temperature (boiling water), or combined high temperature and pressure (autoclave), toxic chemicals, or physical removal (filtration). 

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