Case of the Month - March 2020 Case of the month archive A 67 year-old man who had a kidney transplant from a deceased donor in 2010 was seen for a screening colonoscopy. His last colonoscopy was 10 years ago and was normal. An ulcerated lesion was identified in the transverse colon (see Figure 1). Biopsies were done and submitted to histology. The biopsy was evaluated with routine H & E stains. PAS (Figures 2 and 3) and GMS stains highlighted microorganisms while acid-fast, mucicarmine and Fite stains were negative. What is the organism? Figure 1 - ulcer in transverse colon. Figure 2 - PAS stain, 100X magnification. The micro- organisms indicted by hellow arrows are 2 to 3 μm in greatest dimension. Figure 3 - PAS stain, 100X magnification. The micro- organisms indicted by hellow arrows are 2 to 3 μm in greatest dimension.