What Are They, Treatment, and More

Author:Alyssa Haag

Editors:Ahaana Singh,Ian Mannarino, MD, MBA

Illustrator:Aileen Lin

What is coccobacilli?

Coccobacilli refers to various types of bacteria that are shaped like short rods or ovals. Their shape is a combination of a cocci, or round bacteria, and bacillus, or rod-shaped bacteria. Coccobacilli bacteria are thus characterized as short rods and can sometimes be confused for cocci bacteria.

Another way to categorize bacteria is by observing their ability to absorb a Gram stain, which is a test for bacteria. Bacteria can be classified as either Gram positive, if they absorb the stain and are purple in color, or Gram negative, if they do not absorb the stain and turn pink in color. Knowing the shape and Gram stain of bacteria can assist healthcare providers in diagnosing and treating infections caused by specific bacteria.

There are many different types of both Gram-positive and Gram-negative coccobacilli bacteria that can cause disease in humans. Bacterial vaginosis, which presents in women as a yellow or white discharge and fishy vaginal odor, is caused by the Gram-negative coccobacilli, Gardenella vaginalis. The Gram-negative coccobacilli, Haemophilus influenza can cause a variety of infections, including meningitis, an infection that results in inflammation of the brain and spinal cord, as well as pneumonia, an infection of the lungs. Some additional coccobacilli bacteria include Gram-negative Yersinia pestis, responsible for the devastating “Black Plague” of the 14th century; Gram-negative Bordetella pertussis is responsible for “whooping cough”, which observed mostly in children with a characteristic “whoop” sound while inhaling; and Gram negative Chlamydia trachomatis, responsible for the sexually transmitted infection, chlamydia. In addition to these, there are several other bacterias that are also characterized as coccobacilli.

How do you treat a coccobacilli infection?

Various coccobacilli bacteria can cause a range of symptoms and diseases; thus, treatment depends on the type of illness an individual has. However, antibiotics are usually the first step in treating coccobacilli bacterial infections. There are also vaccines available for specific coccobacilli that can mitigate the risk of future infection. Vaccines against meningitis (Haemophilus influenzae), the plague (Yersinia pestis), and whooping cough (Bordetella pertussis) are widely used and have reduced infection rates of these bacterias dramatically.

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What are the most important facts to know about coccobacilli?

Coccobacilli refers to the shape of bacteria that is an intermediate of the cocci and bacillus shapes. Coccobacillis can be either Gram positive or Gram negative and cause infections in humans. If an individual is infected, antibiotics are a usual first line treatment. There are also vaccines available for specific coccobacilli bacteria that have greatly reduced the incidence of certain infections.

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Related links

Bacterial Structure and Functions
Bordetella pertussis (Pertussis/whooping cough)
Gardnerella vaginalis (Bacterial vaginosis)
Haemophilus influenzae

Resources for research and reference

Brucellosis. (2018). New York State Departmenrt of Health. Retrieved December 4, 2020, from

Mishori, R., McClaskey, E. L., & WinklerPrins, V. J. (2012). Chlamydia Trachomatis Infections: Screening, Diagnosis, and Management. American Family Physician,  86(12): 1127–1132. Retrieved December 4, 2020, from

Sobel, J. D. (2019). Patient Education: Bacterial Vaginosis (Beyond the Basics). In UpToDate. Retrieved December 4, 2020, from

Yang, D. C., Blair, K. M., & Salama, N. R. (2016). Staying in Shape: the Impact of Cell Shape on Bacterial Survival in Diverse Environments. Microbiology and Molecular Biology Reviews, 80(1): 187–203.