Properties of Bacillus anthracis spores prepared under various environmental conditions

Abstract

Bacillus anthracis makes highly stable, heat-resistant spores which remain viable for decades. Effect of various stress conditions on sporulation in B. anthracis was studied in nutrient-deprived and sporulation medium adjusted to various pH and temperatures. The results revealed that sporulation efficiency was dependent on conditions prevailing during sporulation. Sporulation occurred earlier in culture sporulating at alkaline pH or in PBS than control. Spores formed in PBS were highly sensitive towards spore denaturants whereas, those formed at 45 degrees C were highly resistant. The decimal reduction time (D-10 time) of the spores formed at 45 degrees C by wet heat, 2 M HCl, 2 M NaOH and 2 M H(2)O(2) was higher than the respective D-10 time for the spores formed in PBS. The dipicolinic acid (DPA) content and germination efficiency was highest in spores formed at 45 degrees C. Since DPA is related to spore sensitivity towards heat and chemicals, the increased DPA content of spores prepared at 45 degrees C may be responsible for increased resistance to wet heat and other denaturants. The size of spores formed at 45 degrees C was smallest amongst all. The study reveals that temperature, pH and nutrient availability during sporulation affect properties of B. anthracis spores.

Behavioural pattern of vegetative cells and spores of Bacillus cereus as affected by time-temperature combinations used in processing of Indian traditional foods

“…The wide variations observed in the thermal inactivation pattern of spores of B. cereus could be attributed to one or more of the following (1) characteristics of strains of B. cereus with environmentally induced resistance due to dipicolinic acid content, degree of hydration and mineral content (Marquis and Shin 1994;Palop et al 1996;Mazas et al 1999b;Melly et al 2002;Baweja et al 2008), (2) temperatures which have induced spore formation as well as other conditions prevailing during sporulation (Condon et al 1992;Baweja et al 2008) and (3) heterogeneity in the cluster of spores with respect to germination and/or survival (Byrne et al 2006).…”

“…However, spores, which are formed from the same vegetative cells, achieve resistance to heat processing. This resistance is invariably attributed to a metabolically inactive complex of nucleic acids and calcium dipicolinic acid formed under a set of prevailing unfavourable conditions (Murrel 1988;Nicholson et al 2000;Baweja et al 2008).…”

Bacillus cereus growth and biofilm formation: the impact of substratum, iron sources, and transcriptional regulator Sigma 54

“…Similar to our findings, spores of B. anthracis developed in nutrient deprived conditions submerged in PBS, displayed lower resistance properties against wet heat and several chemical denaturants, such as acidic or alkali pH and hydrogen peroxide. These spores contained the same level of DPA as the spores from the control culture but may have an altered composition due to lack of precursors for synthesis of different spore components (Baweja et al 2008). Similarly, in our study there was no correlation found between the heat resistance of spores derived from different conditions and their DPA content measured according to (Kort et al 2005) (not shown).…”

“…Ryu and Beuchat (2005) exposed biofilms of B. cereus formed in TSB to air which resulted in increased spore formation at 22 °C and high relative humidity of 97 and 100 %, whereas exposure to air with low humidity (85%) did not affect sporulation but resulted in death of vegetative cells. Baweja et al (2008) transferred planktonic early stationary culture of Bacillus anthracis into PBS and observed significantly increased sporulation efficiency up to 50% compared to 5% for the control within 8 h, confirming the sporulation promoting effect of nutrient deprivation.…”

“…Sporulation temperature has a large effect on spore heat resistance of B. cereus with a 10 fold difference in decimal reduction time (D 100°C ) for spores formed at 20 compared to 45⁰C (González et al 1999). Most studies show lower impact of different factors such as sporulation medium, level of nutrients or pH on spore heat resistance, reporting between 1.3 to 6 fold changes in decimal reduction values (D-values) (Mazas et al 1995, Baweja et al 2008, Baril et al 2012). …”