Elucidation of Strongyloides stercoralis by bacterial-colony displacement.

Two cases of unsuspected Strongyloides stercoralis infection were elucidated by the displacement of bacterial colonies on primary plating media. Observation of primary plates inoculated for the diagnosis of bacterial pneumonia or gastroenteritis revealed that normal flora colonies had been moved and were aligned in a pathway, or track. This unusual colony alignment prompted us to request a stool for the examination of parasites, and S. stercoralis was found. It was concluded that the parasite is capable of motility on agar surfaces, resulting in the displacement of bacterial colonies that make up the normal flora.