INTERACTION OF IODINE WITH BACILLUS-SUBTILIS SPORES AND SPORE FORMS

Buffered solutions of iodine (pH 7.0) were effective against Bacillus subtilis spores, but concentrations and contact times for effective sp oricidal action were relatively high. Concentrations of 500 to 1000 pp m available iodine with a contact time of 30-45 min were required to p roduce a 3-5 log reduction. Treatment of spores with agents which caus ed progressive extraction of coat protein and cortex hexosamine was as sociated with increased sensitivity to iodine. Treatment of spores wit h iodine produced extraction of spore coat protein which was potentiat ed in the presence of NaOH, but there was no evidence of breakdown of cortex hexosamines or release of dipicolinic acid, either from intact spores or spore protoplasts. Sporicidal concentrations of iodine stimu lated the uptake of (P-32) phosphate over an initial period of 30-40 m in, but phosphate then leaked from the cells; 1000 ppm available iodin e produced total loss within 60 min. Results of this investigation are consistent with previous findings which suggest that the resistance o f spores to biocides is related to the barrier properties of the spore outer layers and that the sporicidal action of halogen-releasing agen ts is related to their ability to cause coat and cortex degradation, l eading to rehydration of the spore protoplast and allowing diffusion t o their site of action on the underlying protoplast.