Coccobacilli are a type of bacteria that are shaped like short rods or ovals. Their shape is intermediate between cocci (i.e., round bacteria) and bacilli (i.e., rod-shaped bacteria). Coccobacilli are thus usually described as short rods and can sometimes be mistaken for cocci due to their similar, rounded shape.One common method for classifying bacteria involves examining their staining properties under a microscope. The Gram stain is the most widely used technique for this purpose. Depending on their cell wall structure, bacteria are classified as either Gram-positive, which appear purple because they are able to retain the stain, or Gram-negative, which cannot retain the stain and appear pink after counterstaining.
Classifying bacteria based on their shape and Gram stain characteristics is important for identifying the infectious agent and guiding appropriate treatment.
Many different species of Gram-positive and Gram-negative coccobacilli can cause disease in humans. Among Gram-negative coccobacilli, Gardnerella vaginalis is the agent responsible for bacterial vaginosis, a condition characterized by white or yellow vaginal discharged and a distinctive fishy vaginal odor. Haemophilus influenzae, also Gram-negative, can cause various infections including meningitis, an inflammation of the membranes surrounding the brain and spinal cord, and pneumonia, or lung infection. Yersinia pestis is the Gram-negative coccobacillus that caused the devastating “Balck Plague” of the 14th century. Bordetella pertussis is responsible for whooping cough, a childhood infection characterized by severe coughing followed by the distinctive “whoop” sound during inhalation. Chlamydia trachomatis is the Gram-negative coccobacillus causing chlamydia, a common sexually transmitted infection. Finally, Brucella spp. are coccobacilli responsible for brucellosis, a zoonotic infection that can be transmitted from animals to humans. Brucellosis may affect multiple organ systems and typically presents with non-specific symptoms such as fever.
