The differential susceptibility of spores from virulent and attenuated Bacillus anthracis strains to aldehyde- and hypochlorite-based disinfectants

Correlations between available primary amines, endospore coat thickness, and alkaline glutaraldehyde sensitivity for spores of select Bacillus species

Alkaline glutaraldehyde (GTA) is a high‐level chemical disinfectant/sterilant and has a broad microbial kill spectrum. The precise antimicrobial mechanism of GTA remains debated. GTA kill times are extremely variable across different organisms, illustrating the need for a better understanding of GTA kill mechanisms related to different organisms. A commonly proposed GTA kill mechanism suggests that it works by cross‐linking accessible primary amines on important surface proteins. If true, the antimicrobial activity of GTA may directly correlate to the number of these available functional groups. Bacillus species form highly resistant bacterial endospores that are commonly used as one of the most stringent test organisms for disinfection and sterilization. In this study, we compared the log reduction times of alkaline GTA on spores from 4 Bacillus species to fluorescent profiles generated using Alexa Fluor™ amine‐reactive dyes. GTA kill times were also compared to mean spore coat thicknesses as measured with scanning electron microscopy (SEM). Fluorescence values generated from bound amine‐reactive dye showed a strong, positive correlation to GTA susceptibility, as measured by GTA 6‐log₁₀ reduction times. Spore coat thickness also showed a strong, positive correlation to reduction time values. Results support the hypothesis that GTA kill times are directly related to the number of available primary amines on bacterial endospores. Results also indicated that the killing efficacy of GTA may be influenced by its ability to penetrate the spore coat to reach additional targets, suggesting that damaging important biomolecules beyond surface proteins may be involved in GTA killing mechanisms.

Decontamination of Personal Protective Equipment

Exploratory field analyses of the inactivation capacity of disinfectants on contaminated personal protective equipment (PPE) are required to select a suitable surrogate for biohazardous agents like spores of Bacillus anthracis. The objectives of our study were (1) the determination of an appropriate surrogate for the inactivation of spores of B. anthracis with peracetic acid (PAA), and (2) application of optimized inactivation conditions for an effective decontamination of PPE with PAA under field conditions. For inactivation studies, B. anthracis spores from different strains and B. thuringiensis spores were fixed by air drying on carriers prepared from PPE fabric. Time and concentration studies with PAA-based disinfectants revealed that the spores of the B. thuringiensis strain DSM 350 showed an inactivation profile comparable to that of the spores of the B. anthracis strain with the highest stability, implying that B. thuringiensis can serve as an appropriate surrogate. Rapid (3 to 5 minutes) and effective surface decontamination was achieved with 2% PAA/0.2% surfactant. In field studies, PPE contaminated with spores of B. thuringiensis was treated with the disinfectant. Optimizing the decontamination technique revealed that spraying in combination with brushing was effective within 5 minutes of exposure.

Decontamination Efficacy and Skin Toxicity of Two Decontaminants against Bacillus anthracis

Decontamination of bacterial endospores such as Bacillus anthracis has traditionally required the use of harsh or caustic chemicals. The aim of this study was to evaluate the efficacy of a chlorine dioxide decontaminant in killing Bacillus anthracis spores in solution and on a human skin simulant (porcine cadaver skin), compared to that of commonly used sodium hypochlorite or soapy water decontamination procedures. In addition, the relative toxicities of these decontaminants were compared in human skin keratinocyte primary cultures. The chlorine dioxide decontaminant was similarly effective to sodium hypochlorite in reducing spore numbers of Bacillus anthracis Ames in liquid suspension after a 10 minute exposure. After five minutes, the chlorine dioxide product was significantly more efficacious. Decontamination of isolated swine skin contaminated with Bacillus anthracis Sterne with the chlorine dioxide product resulted in no viable spores sampled. The toxicity of the chlorine dioxide decontaminant was up to two orders of magnitude less than that of sodium hypochlorite in human skin keratinocyte cultures. In summary, the chlorine dioxide based decontaminant efficiently killed Bacillus anthracis spores in liquid suspension, as well as on isolated swine skin, and was less toxic than sodium hypochlorite in cultures of human skin keratinocytes.