Isolation of Bacillus anthracis from soil in selected high-risk areas of Zimbabwe

Aims To isolate Bacillus anthracis from cattle carcass burial sites from high-risk districts in Zimbabwe. Methods and Results Soil samples were collected from carcass burial sites from seven areas, including two national game parks. Samples were collected from top 5–10 cm, and for spore extraction, 25 g of soil was suspended in sterile distilled water overnight. Supernatants were filtered through 0·45-μm pore cellulose nitrate, deposits suspended in 5 ml phosphate-buffered saline, aliquoted and heated at temperature regimen of 65, 70, 75 and 80°C for 15 min. Samples were plated onto PLET agar. B. anthracis isolates were identified using growth morphology and PCR detecting pXO1 and pXO2 virulence plasmids. From samples heated at 75°C for 15 min, B. anthracis were isolated from 9 of 81 (11·1%) soil samples representing five of the seven sampled areas. Conclusions We isolated B. anthracis from soil collected from carcass burial sites. PCR targeting virulence plasmids provided a rapid confirmation of B. anthracis. Significance and Impact of the study The positive isolation indicated that some carcass burial sites may retain viable spores for at least 12 months after the previous outbreak, which suggests that they may be important sources of B. anthracis and new disease outbreaks.