PowerPoint Contents
Author: Rebecca Buxton
Citation: Rebecca Buxton. 2007.
Sputum–gram-negative bacilli.
Publication Date: February 2007
Escherichia coli (Enlarged view) Enlarged view
Slide 1. Escherichia coli
These gram-negative bacilli vary little in size and shape in this stained preparation and are "plumper" than Haemophilus influenzae.
Because the ends of some bacilli stain more densely than does the middle (a characteristic called "bipolar staining"), the bacilli resemble safety pins. Bipolar staining is common in enteric gram-negative bacilli, and if not carefully examined, the organisms may appear to be diplococci rather than bacilli. Several bacteria are present in the cytoplasm of neutrophils.
Enterobacter cloacae (Enlarged view)
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.
Pseudomonas aeruginosa (Enlarged view)
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.
Stenotrophomonas maltophilia (Enlarged view)
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.
Acinetobacter baumanii (Enlarged view)
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.
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