Resistance of Bacillus Spores to Combined Sporicidal Treatments

Abstract

Summary. Moist heat at 82° (100° for Bacillus stearothermophilus) and solutions of 0.2% w/v chlorocresol or 0.01% w/v benzalkonium chloride at 24° separately showed no sporicidal activity against B. pumilis, B. stearothermophilus, B. subtilis and B. subtilis var. niger. Spores of the last organism were the most sensitive to γ radiation, the D value being 0.16 Mrad. Prior irradiation with a dose of 0.16 Mrad brought about only a slight increase in the sensitivity of the spores to moist heat. The presence of bactericide during irradiation did not affect radiation resistance. Inactivation rates were greater when the spores were heated in the presence of a bactericide than in aqueous suspension and benzalkonium chloride was more active than chlorocresol. Chlorocresol enhanced the heat activation of B. stearothermophilus at 100°. Irradiation in the presence of 0.2% w/v chlorocresol or 0.01% w/v benzalkonium chloride had no effect on the subsequent resistance of the spores when heated in the presence of these bactericides. It is concluded that it is unlikely that combinations of moist heat, radiation and bactericides, each less severe than when used in an accepted sterilization process, will lead to an alternative process which, while less damaging to the materials being sterilized, would still maintain the accepted standards of freedom from contamination.

Bacterial spores and chemical sporicidal agents

“…In contrast, concentrations as low as 0.2% (phenol), 0.08% (cresol), and 0.02% (chlorocresol) (wt/vol) are all effective inhibitors of germination (173). Furthermore, sporicidal activity is greatly accelerated when phenolics are used at elevated temperatures (33). Such a process, utilizing 0.2% (wt/vol) chlorocresol at 98 to 100'C, was for many years a pharmacopoeial process in the United Kingdom for sterilizing certain injectable and ophthalmic products, but is no longer official.…”

“…These involve a combination of a chemical and a physical process or of two chemical agents (1 The bactericidal and sporicidal activity of a biocide increases with increasing temperature. For example, the temperature coefficient (0) per 1C rise in temperature for the phenolic agent chlorocresol is 1.1 (33). If the temperature is increased from 20 to 1000C, then assuming that 0 is the same over the entire temperature range, the activity increases by >2,000-fold (0100-20 = 1.180 = 2,104).…”

Sporicidal activity of chemical and physical tissue fixation methods.

“…At the concentrations used and for the times recommended, aldehyde fixatives may be considered to be sporicidal and thus effective as tissue sterilants. 18 When various mixtures of alcohol and polyethylene glycol (PEG) are used as fixatives, for example Kryofix or Spuitfix, the fixation of tissue is excellent; however, the sterilising effects on clinical material so fixed have not been investigated. It is known that 70% wt/vol alcohol will kill many Gram positive and Gram negative bacteria, some viruses, and some fungi, justifying its use as an effective antiseptic and disinfecting medium in many applications.…”

Microbiological Applications of the Inactivation of Antibiotics and Other Antimicrobial Agents

“…6 ) that cysteine could replace thioglycollate in such media. Thioglycollate does not always enhance the recovery of bacteria exposed to a mercury compound ;Briggs & Yazdany (1974) have shown that spores of bacilli treated with phenylmercuric nitrate gave similar counts on Antibiotic Assay Medium with or without thioglycollic acid. In a study with merthiolate, Price (1950) reported that simple dilution was far less effective than a chemical inactivator in reversing the activity of the disinfectant.…”