Aberrant staining with Grocott's methenamine silver: utility beyond fungal organisms

GMS is a chromic acid, sodium bisulfate stain that precipitates silver ions in fungal polysaccharide walls, producing the characteristic black stain on light microscopy. It is helpful to recognize aberrant GMS staining to avoid misdiagnosis of fungal elements. GMS stains several nonfungal human pathogens and may be a particularly useful diagnostic aid when the infectious condition is not clinically suspected or the number of organisms is sparse and otherwise difficult to visualize by routine staining methods.