Dose-response analysis of Bacillus thuringiensis HD-1 cry- spore reduction on surfaces using formaldehyde with pre-germination

Decontamination of Soil Contaminated at the Surface with Bacillus anthracis (Anthrax) Surrogate Spores Using Steam Vapor

In the event of a wide-area release of Bacillus anthracis spores, soils and other outdoor materials will likely become contaminated with the biological agent. Soils may also become contaminated with B. anthracis when livestock or wildlife succumb to anthrax disease. This study was conducted to assess the in situ remediation of soil using steam vapor to inactivate a B. anthracis spore surrogate (Bacillus atrophaeus) inoculated into soil samples. Tests were conducted using small columns (~0.04 m3 of soil) filled with either loam, clay, or a sandy soil. Following steam treatment, the B. atrophaeus spores were recovered from the test and positive control soil samples via liquid extraction and this liquid was subsequently dilution plated to quantify viable spores in terms of colony-forming units. Decontamination efficacy was assessed as a function of soil type, soil depth, soil moisture, soil temperature, and steam exposure time. Results showed that spore inactivation improved with increasing steam exposure time and diminished with depth. The clay soil generally exhibited the highest soil temperatures and correspondingly showed the highest inactivation of spores. Adding moisture to the soil prior to the steam treatment increased heat transfer within the soil column, and sealing the columns to mitigate steam leakage increased spore inactivation. The results showed that a steam mass of 40-50 kg applied per square meter of soil surface was sufficient to inactivate bacterial spores to depths between 7 and 10 cm. With bacterial spores on the soil column surface, a contact time of 15 min with the steam vapor at 99°C was sufficient for complete inactivation. These findings provide a foundation for estimating costs and time requirements for applying steam to the soil surface, and further confirmatory testing at field-scale is suggested.

Dose-response analysis of Bacillus thuringiensis HD-1 cry- spore reduction on surfaces using formaldehyde with pre-germination

AIM

To establish a basis for rapid remediation of large areas contaminated with Bacillus anthracis spores.

METHODS AND RESULTS

Representative surfaces of wood, steel and cement were coated by nebulization with B. thuringiensis HD-1 cry- (a simulant for B. anthracis) at 5.9 ± 0.2, 6.3 ± 0.2 and 5.8 ± 0.2 log10 CFU per cm² , respectively. These were sprayed with formaldehyde, either with or without pre-germination. Low volume (equivalent to ≤2500 L ha^-1 ) applications of formaldehyde at 30 g l^-1 to steel or cement surfaces resulted in ≥4 or ≤2 log10 CFU per cm² reductions respectively, after 2 h exposure. Pre-germinating spores (500 mmol l^-1 l-alanine and 25 mmol l^-1 inosine, pH 7) followed by formaldehyde application showed higher levels of spore inactivation than formaldehyde alone with gains of up to 3.4 log10 CFU per cm² for a given dose. No loss in B. thuringiensis cry- viability was measured after the 2 h germination period, however, a pre-heat shock log10 reduction was seen for B. anthracis strains: LSU149 (1.7 log10), Vollum and LSU465 (both 0.9 log10), LSU442 (0.2 log10), Sterne (0.8 log10) and Ames (0.6 log10).

CONCLUSIONS

A methodology was developed to produce representative spore contamination of surfaces along with a laboratory-based technique to measure the efficacy of decontamination. Dose-response analysis was used to optimize decontamination. Pre-germinating spores was found to increase effectiveness of decontamination but requires careful consideration of total volume used (germinant and decontaminant) by surface type.

SIGNIFICANCE AND IMPACT OF THE STUDY

To be practically achievable, decontamination of a wide area contaminated with B. anthracis spores must be effective, timely and minimize the amount of materials required. This study uses systematic dose-response methodology to demonstrate that such an approach is feasible.