The effects of biocides (antiseptics and disinfectants) on the endospores of Rhinosporidium seeberi.

ABSTRACT

No data exists on the activity of biocides (antiseptics and disinfectants) on Rhinosporidium seeberi that causes rhinosporidiosis in humans and animals. On account of the inability to culture R. seeberi, in vitro, dyes were used to assess the morphological integrity and viability of biocide-treated endospores that are considered to be the infective stage of this pathogen. Evan's Blue (EvB) identifies the morphological integrity of the endospores while MTT (3-[4, 5-dimethylthiazol-2yl]-2, 5-diphenyl tetrazolium bromide) identifies metabolic activity through its reduction by cellular dehydrogenases to microscopically visible deposits of insoluble formazan. MTT-negativity has earlier been shown to correlate with absence of growth of yeast and mycelial fungi in culture and could thus indicate the loss of viability of MTT-negative rhinosporidial endospores. Hydrogen peroxide, glutaraldehyde, chloroxylenol, chlorhexidine, cetrimide, thimerosal, 70% ethanol, iodine in 70% ethanol, 10% formalin, povidone-iodine, sodium azide and silver nitrate were tested on freshly-harvested endospores and all biocides caused metabolic inactivation with or without altered structural integrity as shown by absence of MTT-staining after 3, 24 or 36 hour after exposure, while EvB stained only the endospores treated with sodium azide, ethanol, thimerosal, chloroxylenol, glutaraldehyde and hydrogen peroxide. With clinically useful biocides - chlorhexidine, cetrimide-chlorhexidine, 70% ethanol, povidone-iodine and silver nitrate, a total period of exposure of endospores to the biocide, for seven minutes, produced metabolic inactivation of the endospores. Anti-rhinosporidial antiseptics that could be used in surgery on rhinosporidial patients include povidone-iodine in nasal packs for nasal and naso-pharyngeal surgery, chlorhexidine and cetrimide-chlorhexidine on the skin, while povidone-iodine and silver nitrate could have application in ocular rhinosporidiosis.