The eponymous German bacteriologist is Petri, a five-letter word. Petri was a German microbiologist and botanist who is best known for his invention of the Petri dish, a shallow cylindrical glass lidded dish that is used to culture cells. He also developed the agar plate technique, which is used to isolate pure cultures of bacteria. Petri's work revolutionized the field of bacteriology and helped to advance the understanding of infectious diseases.