Difference between the spore sizes of Bacillus anthracis and other Bacillus species

Abstract

Aims: To determine the size distribution of the spores of Bacillus anthracis, and compare its size with other Bacillus species grown and sporulated under similar conditions. Methods and Results: Spores from several Bacillus species, including seven strains of B. anthracis and six close neighbours, were prepared and studied using identical media, protocols and instruments. Here, we report the spore length and diameter distributions, as determined by transmission electron microscopy (TEM). We calculated the aspect ratio and volume of each spore. All the studied strains of B. anthracis had similar diameter (mean range between 0·81 ± 0·08 μm and 0·86 ± 0·08 μm). The mean lengths of the spores from different B. anthracis strains fell into two significantly different groups: one with mean spore lengths 1·26 ± 0·13 μm or shorter, and another group of strains with mean spore lengths between 1·49 and 1·67 μm. The strains of B. anthracis that were significantly shorter also sporulated with higher yield at relatively lower temperature. The grouping of B. anthracis strains by size and sporulation temperature did not correlate with their respective virulence. Conclusions: The spores of Bacillus subtilis and Bacillus atrophaeus (previously named Bacillus globigii), two commonly used simulants of B. anthracis, were considerably smaller in length, diameter and volume than all the B. anthracis spores studied. Although rarely used as simulants, the spores of Bacillus cereus and Bacillus thuringiensis had dimensions similar to those of B. anthracis. Significance and Impact of the Study: Spores of nonvirulent Bacillus species are often used as simulants in the development and testing of countermeasures for biodefence against B. anthracis. The data presented here should help in the selection of simulants that better resemble the properties of B. anthracis, and thus, more accurately represent the performance of collectors, detectors and other countermeasures against this threat agent.

Evaluating the long‐term persistence of Bacillus spores on common surfaces

“…They are relatively smaller and morphologically different from B. anthracis Sterne, B. thuringiensis or B. cereus (Greenberg et al ., 2010). This was previously found to result in lower adhesiveness of B. atrophaeus spores (Carrera et al ., 2007). …”

“…Therefore, non‐pathogenic surrogates for B. anthracis spores that mimic the behaviour of the species of interest are useful for experimental purposes. Based on previous theoretical studies, the following spores of B. anthracis surrogates were used for this work – B. anthracis Sterne (attenuated non‐pathogenic strain of B. anthracis ) , B. cereus (common foodborne pathogen sharing morphological similarities with B. anthracis ) , B. thuringiensis (commonly used to produce a toxin used as an insecticide that is morphologically and genetically similar to B. anthracis ) and B. atrophaeus (most commonly used surrogate) (Carrera et al ., 2007; Greenberg et al ., 2010; Tufts et al ., 2013). While the recovery of spores from surfaces has been studied (Hodges et al ., 2010; Rose et al ., 2011; Calfee et al ., 2013), to date, no published studies have experimentally compared different surrogates of pathogenic B. anthracis spores under indoor conditions.…”

“…The robustness of Gompertz models to predict microbial populations under different temperatures has made them versatile for modelling purposes. The broken‐line model (Carrera et al ., 2007; Rogers et al ., 2011) was used to account for abrupt changes in the non‐linearity in inactivation curve. Points of abrupt changes known as ‘break points’ were developed originally to provide a better understanding of the kinetic parameters at different points of departure in the inactivation curve.…”

Coherent X-ray diffractive imaging on the single-cell-level of microbial samples

“…Carrera et al used Percoll gradients to determine the mass density of comparably large amounts of endospores from B. thuringiensis 4055 and B. subtilis 1031 [38]. From the determined density they calculated the mass of a single endospore by using an ellipsoid size model with size estimations from electron microscopy studies [37].…”

“…In addition, the iterative phase reconstructions using the mHIO algorithm could These values can be compared with measurements of the wet weight, wet and dry density of endospores [38,304]. Carrera et al used Percoll gradients to determine the mass density of comparably large amounts of endospores from B. thuringiensis 4055 and B. subtilis 1031 [38].…”