The doctor suspected his diarrhea was caused by an amebic infection.

amebic 是形容词，由名词 ameba（阿米巴，一种单细胞微生物）加上形容词后缀 -ic 构成，表示"与阿米巴相关的"或"由阿米巴引起的"。amebic infection 特指由阿米巴原虫引起的感染性疾病。