Slide 2. Enterobacter cloacae
The plump, gram-negative bacilli vary somewhat in size. Enteric gram-negative bacilli, such as Enterobacter, Klebsiella, and Escherichia coli, are difficult to differentiate by their appearance on Gram stain.

Slide 3. Pseudomonas aeruginosa
These long, slender, gram-negative bacilli are nearly uniform in size. Pseudomonas species tend to be longer and slimmer than enteric gram-negative bacilli, such as Klebsiella and Escherichia coli, and bipolar staining is unusual. Despite such differences, however, distinguishing Pseudomonas species from other gram-negative bacilli is often difficult.

Slide 4. Stenotrophomonas maltophilia
This specimen was obtained by bronchoscopy from a neutropenic recipient of a bone-marrow transplant. Neutrophils are absent, but the presence of ciliated bronchial epithelial cells confirms the lower respiratory tract as the source. Ciliated bronchial epithelial cells are rarely found in expectorated sputum but are common in bronchoscopic specimens. Thin, long, faintly-stained bacilli could suggest a species of Pseudomonas or Stenotrophomonas maltophilia.

Slide 5. Acinetobacter baumanii
Many of the plump, very short, gram-negative bacilli are nearly coccal. Their appearance is characteristic of Acinetobacter species, although they are sometimes mistakenly identified as Neisseria species.