Watch Bacterial Shapes Video
Prokaryotes (bacteria) are smaller (1-10 micrometers, um) than Eukaryotic cells and can be distinguished by the lack of a membrane-bound nucleus. Prokaryotic cells have 3 major shapes: cocci, bacilli or spirilla.
Bacterial cells can be arranged in different groups or patterns. These cells can be arranged singly, in pairs (diplo), groups of 4 (tetrads), chains (strepto), clusters (staphylo), packets of 8 or 16 (sarcinae), or hinged together (palisades).
The following types of bacteria have a rod or bacillus shape: Bacillus anthracis (anthrax), Lactobacillus acidophilus (yogurt), and Bacillus megaterium, which consists of long chains of rods called (streptobacillus). Corynebacterium diphtheriae (diphtheria) and Clostridium tetani (tetanus) are club-shaped bacteria hinged together in an arrangement called palisades.
Many Gram-positive bacteria have a spherical shape called coccus. These cocci can be arranged in groups of 2 (diplococci) like Streptococcus pneumoniae (pneumonia) and Neisseria gonorrhoeae (gonorrhea), or in long chains like Streptococcus pyogenes (strep throat), or in clusters like Staphylococcus aureus (food poisoning and skin infections).
Other bacteria are spiral-shaped. For example, Vibrio cholera (cholera) forms a comma-shaped spiral. Other bacteria, such as Treponema pallidum (syphilis), are considered spirochetes, because they form a more tightly-coiled spiral.
Bacteria that have a waxy cell wall, such as Mycoplasma pneumoniae have an irregular shape called pleiomorphic. These bacteria vary in shape from long and filamentous to round.
Can you correctly identify each of the following bacterial shapes?
Can you correctly identify each of the following bacterial cell arrangements?