Doctor of Philosophy (PhD)


Plant, Environmental Management and Soil Sciences

Document Type



Bacillus anthracis, the etiological agent of the disease anthrax, is a bacteria of great importance, both in the past and today. Despite this importance, many questions remain regarding defending against its use as a biological weapon, the bacteria's variation in virulence, and its epidemiology in nature. Using Etest strips (AB BIODISK, Solna, Sweden) to measure the MICs, 25 genetically diverse isolates of B. anthracis were tested to determine their susceptibility to seven clinically relevant antimicrobial agents. Using the NCCLS MIC breakpoints for staphylococci, three isolates were found to be resistant to penicillin and negative for beta-lactamase production. From a group of investigations, results indicated B. anthracis virulence is related to clonality and the copy numbers per cell of the virulence plasmids, pXO1 and pXO2. Isolates were characterized with respect to their plasmid copy number (pXO1/2) using a novel method of quantitative PCR and the numbers differ greatly from previous reports. Anthrax Vaccine with Adjuvant (AVA) vaccinated guinea pigs were challenged with 20 B. anthracis strains representative of worldwide genetic diversity. A virulence model was constructed by combining the survival, plasmid copy number, and genotyping (based on multilocus variable number tandem repeat analysis typing) data of each isolate. The model obtained was validated using a randomly chosen set of 12 B. anthracis isolates and verified model robustness. Carcass disposal methods, incineration and burial, are recommended to decrease or prevent environmental spore contamination. The extent of contamination from an anthrax carcass is almost totally unknown despite the method of disposal. Studies of environmental contamination by spores of B. anthracis from infected carcasses have only recently been possible because of new technologies. A method utilizing real-time quantitative PCR was developed to quantitate B. anthracis in environmental samples. Absolute quantitation was made possible by the use of clones. This method has allowed the evaluation of the environmental contamination by the different carcass disposal methods and by scavenging of the carcass. The results support the complete burning of a carcass soon after death as the method choice to decrease environmental contamination for the disposal of anthrax affected carcasses.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Martin Hugh-Jones