Pulmonary granuloma is a common lesion for which gram-negative bacteria are
rarely implicated as a cause. Hence, most physicians are unaware of this e
tiology. We isolated a gram-negative bacterium from a surgically resected p
ulmonary granuloma in a 42-year-old, nonimmunocompromised woman. Within the
necrotizing granuloma, numerous organisms also were demonstrated by Gram s
tain, suggesting a cause-disease relationship. Characterization of the bact
erium by sequence analysis of the 16S ribosomal gene, cellular fatty acid p
rofiling, and microbiologic studies revealed a novel bacterium with a close
relationship to Pseudomonas. We propose a new species for the bacterium, P
seudomonas andersonii. These results suggest that the differential diagnosi
s of a lung granuloma also should include this gram-negative bacterium as a
potential causative agent, in addition to the more common infections cause
d by acid-fast bacilli and fungi. This bacterium was shown to be susceptibl
e to most antibiotics that are active against gramnegative bacteria.