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

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.

Human anti-rhinosporidial antibody does not cause metabolic inactivation or morphological damage in endospores of Rhinosporidium seeberi, in vitro.

This report describes the use of the MTT-reduction and Evan's blue-staining tests for the assessment of the viability and morphological integrity, respectively, of rhinosporidial endospores after exposure to sera from rhinosporidial patients with high titres of anti-rhinosporidial antibody. Sera from three patients, with nasal, ocular and disseminated rhinosporidiosis respectively were used, with human serum without anti-rhinosporidial antibody for comparison, with or without added fresh guinea pig serum as a source of complement. All four sera tested, with or without guinea-pig serum, had no effect on the morphological integrity or the viability of the endospores and it is suggested that anti-rhinosporidial antibody has no direct protective role against the endospores, the infective stage, in rhinosporidiosis. This finding is compatible with the occurrence of chronicity, recurrence and dissemination that are characteristic of rhinosporidiosis despite the presence of high titres of anti-rhinosporidial antibody in patients with these clinical characteristics. The possible occurrence of humoral mechanisms of immunity that involve anti-rhinosporidial antibody with cells such as leucocytes and NK cells, in vivo, cannot yet be discounted, although the presence of high titres of anti-rhinosporidial antibody in patients with chronic, recurrent and disseminated lesions might indicate that such antibody is non-protective in vivo.