Characterization of Bacillus anthracis replication and persistence on environmental substrates associated with wildlife anthrax outbreaks

Abstract

Anthrax is a zoonosis caused by the environmentally maintained, spore-forming bacterium Bacillus anthracis, affecting humans, livestock, and wildlife nearly worldwide. Bacterial spores are ingested, inhaled, and may be mechanically transmitted by biting insects or injection as occurs during heroin-associated human cases. Herbivorous hoofstock are very susceptible to anthrax. When these hosts die of anthrax, a localized infectious zone (LIZ) forms in the area surrounding the carcass as it is scavenged and decomposes, where viable populations of vegetative B. anthracis and spores contaminate the environment. In many settings, necrophagous flies contaminate the outer carcass, surrounding soils, and vegetation with viable pathogen while scavenging. Field observations in Texas have confirmed this process and identified primary browse species (e.g., persimmon) are contaminated. However, there are limited data available on B. anthracis survival on environmental substrates immediately following host death at a LIZ. Toward this, we simulated fly contamination by inoculating live-attenuated, fully virulent laboratory-adapted, and fully virulent wild B. anthracis strains on untreated leaves and rocks for 2, 5, and 7 days. At each time point after inoculation, the number of vegetative cells and spores were determined. Sporulation rates were extracted from these different time points to enable comparison of sporulation speeds between B. anthracis strains with different natural histories. We found all B. anthracis strains used in this study could multiply for 2 or more days post inoculation and persist on leaves and rocks for at least seven days with variation by strain. We found differences in sporulation rates between laboratory-adapted strains and wild isolates, with the live-attenuated strain sporulating fastest, followed by the wild isolates, then laboratory-adapted virulent strains. Extrapolating our wild strain lab results to potential contamination, a single blow fly may contaminate leaves with up to 8.62 x 105 spores per day and a single carcass may host thousands of flies. Replication outside of the carcass and rapid sporulation confirms the LIZ extends beyond the carcass for several days after formation and supports the necrophagous fly transmission pathway for amplifying cases during an outbreak. We note caution must be taken when extrapolating replication and sporulation rates from live-attenuated and laboratory-adapted strains of B. anthracis.

One health approach to mitigate anthrax in Ghana

“…11,12 In various anthrax epidemics in livestock and wildlife in India, Africa, and the United States, both biting (Stomoxys or Tabanus species) and nonbiting (blowfly and chrysoma species) insects have been implicated. 13,14 This mechanical mechanism of transmission causes edema after infection, which develops into the development of painless black lesions on the skin. 11…”

Anthrax disease burden: Impact on animal and human health

“…This Gram-positive bacterium looks blue or purple when stained with Gram's solution under a microscope [33]. Examination of smear preparations made from blood or animal tissue samples with patients under a microscope reveals that these bacteria are grouped in pairs, chains, or alone with a distinctive morphology similar to a bamboo tree segment [34]. Endospores produced by B. anthracis have an oval shape, are positioned in the center, and are no larger in diameter than their vegetative form [35].…”

“…Anthrax had long been associated with soil contamination before B. anthracis was identified as the causative agent [34]. Bacterial spores are resistant to severe temperatures, pressure, pH, drying, solvents, and ultraviolet light [71].…”

Performance appraisal of microbial inoculants treating polluted surface water through bench‐scale investigation

“…in polluted feed water were Proteus mirabilis PM4 (MK559734), Proteus mirabilis PM2 (MK503445), Enterobacter hormaechei EH1 (MK559742), Bacillus anthracis BA1 (MK559745), Vibrio cholerae VC1 (MK559746) and Aeromonas hydrophila AH1 (MK578187). These bacterial species have already been identified in several studies [49][50][51][52][53][54] and are the most prevalent bacterial species in sewage-contaminated surface water. 49,50,55 It is postulated that after being exposed to appropriate environmental conditions, these native bacteria proliferated and were responsible for pollutant degradation in the control reactors in the present study.…”