Commonly Isolated Nonfermenting
Gram-Negative Rods
Clinical Microbiology Review 190
ORGANISM PATHOGENICITY GRAM STAIN CULTURE KEY CHARACTERISTICS
Pseudomonas
aeruginosa
Acinetobacter spp
Stenotrophomonas
maltophilia
Oxidase pos, catalase pos,
motile, grows at 42°C. Grape-
like odor. Only nonfermenter to
produce pyocyanin. (4% don’t.)
Also produces pyoverdin (fluo-
rescent pigment). Resistant to
many antibiotics.
Oxidase neg (differentiates
from N. gonorrhoeae).
Catalase pos. Nonmotile.
Resistant to many antibiotics.
Oxidase neg. Catalase pos.
Motile. Rapid oxidation of
maltose, weaker oxidation of
glucose. Ammonia odor. Resis-
tant to many antibiotics. Disk
diffusion can give false results.
Broth dilution recommended.
Usually not normal flora.
Important cause of nosoco-
mial infections, e.g., burn,
wound, RTI, UTI, bacteremia.
Causes swimmer’s ear &
contact lens keratitis.
Part of normal flora of skin,
pharynx in some. Oppor-
tunistic pathogen. Nosoco-
mial infections, e.g., UTI,
pneumonia, septicemia,
meningitis. 2nd to P. aerugi-
nosa in frequency. A. bau-
manniiis most common.
Not part of normal flora.
Colonizes immunocompro-
mised & cystic fibrosis
patients. Common in hospi-
tal. Nosocomial infections,
e.g., pneumonia.
Long, thin, pale-staining
GNR. Slightly pointed or
rounded ends.
Pleomorphic GNCB in sin-
gles, pairs, short chains.
Can be confused with N.
gonorrhoeae, Moraxella.
May retain crystal violet
in broths & direct smears
& be confused with GPC.
Straight or slightly
curved slender GNR in
singles or pairs.
On SBA: flat spreading
colonies. Usually beta
hemolytic. Dull gray or
blue-green. Metallic
sheen. Grows on MAC &
EMB (lactose neg).
Can grow on most media,
including MAC. Some
produce purplish colonies
(might be mistaken for
lactose fermenter).
On SBA: large, non-
hemolytic. May be light
yellow. Agar may have
lavender-green discol-
oration in areas of heavy
growth. Grows on MAC.
