Last updated on April 21st, 2020
Morphological characteristics of pathogenic bacteria help us to identify them when we stain microbiological specimens and view them under a microscope.
In this blog post, I am going to share some of the distinguishing characteristics shapes of pathogenic bacteria.
- Vibrio cholerae: Comma “Curved” Shaped Gram-negative rod.
- Campylobacter: Curved Gram-negative rods that appear either a comma or S-shaped.
- H. Influenzae: Small, Gram-negative coccobacilli.
- Staphylococci: Spherical, gram-positive cocci arranged in irregular, grape-like clusters.
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Fig: Characteristic shape of S. aureus and V. cholerae Streptococci: Spherical, Gram-positive cocci arranged in chains or pairs.
- Streptococcus pneumoniae (pneumococci): Gram-positive lancet-shaped cocci arranged in pairs (diplococci) or short chains.
- Neisseria (N. gonorrhoeae and N. meningitidis): Gram-negative cocci that resemble paired kidney bean-shaped.
- Bacillus anthracis: Large, Gram-positive rod with square ends, frequently found in chains.
- Clostridium tetani: Gram-positive rod with characteristics “tennis racket shaped” or “Drum stick appearance” (because of terminal spore).
- Clostridium perfringens: Large, Gram-positive, “boxcar” shaped rods.
- Fusobacterium spp: These pleomorphic, long Gram-negative rods often with tapered “pointy” ends.
Fig: Gram Staining reaction of Fusobacterium spp - Corynebacteria: Gram-positive rods that appear club-shaped and are arranged in palisades or in V or L shaped formations (“Chinese-Letter” appearance).
- Listeria monocytogenes: It is a small Gram-positive rod arranged in V or L shaped formations similar to corynebacteria.
- Spirochetes (Treponema, Leptospira, and Borrelia): Thin-walled, flexible, spiral rods (Corkscrew shaped) seen only by darkfield microscope and generally not seen in a standard light microscope.
- Borrelia: They are corkscrew-shaped and are larger than the Treponema, they can be viewed under a light microscope with Giemsa or Wright stains.
