sentences:  Groups of researchers at Merck and Lilly discovered Cephamycin C while looking at penicillin-producing bacteria.This followed their discovery of erythromycin, another antibiotic.Cephamycin C was the first cephem discovered but while it was highly resistant to a lot of beta-lactamases, as is its derivative cefoxitin, it was almost only effective against Gram negative bacteria.