Boiling and Bacillus Spores

摘要

To the Editor: Public healthauthorities rely upon "boil water"advisories to alert consumers if apotable water supply is deemed unsuit-able for consumption. Holding waterat a rolling boil for 1 minute will inac-tivate waterborne pathogens, includingencysted protozoa (1–3). Spores ofBacillus anthracis, the agent that caus-es anthrax, are one of the microorgan-isms most refractory to inactivation bythe boiling water method. This studywas conducted to determine the resist-ance of spores of B. anthracis Sterneand three other strains of Bacillus spp.in boiling water.B. anthracis Sterne (ColoradoSerum Co., Denver, CO) was grownon soil extract peptone beef extractmedium (4). Spores were harvestedfrom the agar plates and washed fourtimes by centrifugation with steriledistilled water, treated with 50%(vol/vol) ethanol while being shakenat 100 rpm for 2 h, then washed anadditional four times by centrifuga-tion with sterile distilled water. Sporesof one of the B. cereus strains wereobtained from a commercial source(Raven Biological Laboratories,Omaha, NE). Spores were producedin broth cultures for the other Bacillusspp. The second B. cereus (ATCC9592) was grown in a generic sporula-tion medium (5), and B. thuringiensisvar. israelensis (ATCC 35646) wasgrown in Schaefer 's medium (6).Spores were purified by gradient sep-aration using RenoCal-76 (BraccoDiagnostics, Princeton, NJ) (6). Sporepreparations were stored in 40%(vol/vol) ethanol at 5°C until used