Experts have identified this bacterium as an uncommon cause of certain pneumonias, particularly in people with lung problems such as asthma or emphysema.Other Gram-negative bacteria that cause pneumonia include E. coli, proteus (found in damaged lung tissue), Enterobacter, Neisseria (N.) meningitidis, and Acetinobacter.Atypical PneumoniaAtypical pneumonias produce mild symptoms and a dry cough.