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Examples of medically important cocci include Enterococcus spp., Neisseria spp., Staphylococcus spp., and ______ spp.
Streptococcus
There are three basic shapes of bacteria: (a) round or spherical bacteria—the ______ (sing., coccus)
cocci
Bacteria divide by binary fission—one cell splits in half to become two ______ cells.
daughter
The size, shape, and morphologic arrangement of various bacteria are easily observed with the ______ light microscope.
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Bacteria vary greatly in size, usually ranging from spheres measuring about 0.2 µm in diameter to 10.0-µm-long ______-shaped bacteria.
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As previously mentioned, the average coccus is about 1 µm in diameter, and the average ______ is about 1 µm wide × 3 µm long.
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Cocci may occur in ______ of four, depending on the particular species.
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Curved and spiral-shaped bacilli are placed into a third ______ grouping.
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______ are examples of coccobacilli, which are short rods resembling elongated cocci.
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______ is an example of a medically important bacillus.
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Vibrio cholerae, the causative agent of ______, is a curved bacillus.
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______ spp. are examples of medically important bacilli.
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A pair of curved bacilli resembles a ______ and is described as having a gull-wing morphology.
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Campylobacter spp., a common cause of ______, have a gull-wing morphology.
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Treponema pallidum, the cause of ______, is a tightly coiled spirochete with a flexible cell wall.
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Borrelia spp. are the causative agents of ______ disease and relapsing fever.
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Bacteria in the genus ______ do not have cell walls and appear in various shapes microscopically.
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A simple ______ is sufficient to determine bacterial shape and morphologic arrangement.
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Study Notes
Bacterial Characteristics
- Bacteria are characterized by cell shape, morphological arrangement, staining reactions, motility, colony morphology, atmospheric requirements, nutritional requirements, biochemical and metabolic activities, specific enzymes produced, pathogenicity, and genetic composition.
Medically Important Bacteria
- Examples of medically important cocci include Enterococcus spp., Neisseria spp., Staphylococcus spp., and Streptococcus spp.
Cell Morphology
- Bacteria vary in size, ranging from 0.2 µm to 10.0 µm in diameter, and can be spherical, rod-shaped, or spiral-shaped.
- The average coccus is about 1 µm in diameter, and the average bacillus is about 1 µm wide × 3 µm long.
Basic Shapes of Bacteria
- Three basic shapes of bacteria:
- Cocci (round or spherical bacteria)
- Bacilli (rectangular or rod-shaped bacteria)
- Spiral-shaped bacteria (sometimes referred to as spirilla)
Binary Fission
- Bacteria divide by binary fission, where one cell splits into two daughter cells.
- The time it takes for one cell to split into two cells is referred to as the generation time.
Morphologic Arrangements
- Cocci may be seen singly or in pairs (diplococci), chains (streptococci), clusters (staphylococci), or packets of four (tetrads) or eight (octads).
- Bacilli may occur singly, in pairs (diplobacilli), in chains (streptobacilli), in long filaments, or branched.
Medically Important Bacilli
- Examples of medically important bacilli include members of the family Enterobacteriaceae, Pseudomonas aeruginosa, Bacillus spp., and Clostridium spp.
Curved and Spiral-Shaped Bacteria
- Curved and spiral-shaped bacteria are placed into a third morphologic grouping.
- Examples include Vibrio spp., Campylobacter spp. (with a gull-wing morphology), and spirochetes (such as Treponema pallidum and Borrelia spp.).
Cell Wall-Deficient Bacteria
- Bacteria may lose their characteristic shape due to adverse growth conditions, becoming cell wall-deficient (CWD) bacteria or L-forms.
- Some CWD bacteria revert to their original shape in favorable growth conditions, while others do not.
Bacteria without Cell Walls
- Bacteria in the genus Mycoplasma lack cell walls, appearing in various shapes under the microscope.
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Description
Test your knowledge on the different morphological arrangements of bacteria such as cocci and bacilli. Learn about how bacteria can appear singly, in pairs, in chains, clusters, tetrads, or octads based on their species and division patterns.
