Coccobacilli are a type of bacteria that are shaped like very short rods or ovals.

The name “coccobacilli” is a combination of the words “cocci” and “bacilli.” Cocci are sphere-shaped bacteria, while bacilli are rod-shaped bacteria. Bacteria that fall between these two shapes are called coccobacilli.

There are many species of coccobacilli, and not all of them cause disease in humans. Keep reading to learn more about some of the most common types of coccobacilli.

You may see bacteria referred to as Gram-positive or Gram-negative. Some bacteria are classified as either Gram-positive or Gram-negative based on the results of a test called a Gram stain.

If you have an infection, your doctor may collect a culture, which is a small sample of bacteria from your blood, urine, or affected body part. They’ll place the sample on a glass slide and allow it to dry out. The next steps include:

  1. staining the slide with a violet dye
  2. applying an iodine-based solution to the slide that forms a large complex with the violet stain
  3. adding a decolorizer to the slide to dehydrate the bacterial cell wall, causing it to shrink and dissolve the outer layer
  4. staining the slide with a reddish-pink color

Gram-positive bacteria have a thick cell wall. This traps the violet stain and iodine complex, making it resistant to the decolorizer. As a result, Gram-positive bacteria look purple under a microscope after a Gram stain.

Gram-negative bacteria have a very thin cell wall and an outer layer, so the decolorizer washes away the violet stain and iodine complex. Under a microscope, Gram-negative bacteria have a reddish-pink color from the second stain.

Gram staining can help your doctor narrow down the type of bacteria that might be causing an infection and choose the most effective antibiotic. However, there are many other ways of categorizing bacteria.

Bacterial vaginosis (Gardnerella vaginalis)

The coccobacillus G. vaginalis can contribute to bacterial vaginosis in women, which happens when bacteria in the vagina are out of balance.

Symptoms include yellow or white vaginal discharge and a fishy-smelling vaginal odor. However, up to 75 percent of women don’t have any symptoms.

Pneumonia (Haemophilus influenzae)

Pneumonia is a lung infection characterized by inflammation. One type of pneumonia is caused by the Gram-negative coccobacillus H. influenzae.

Symptoms of pneumonia caused by H. influenzae include fever, chills, sweating, coughing, trouble breathing, chest pain, and headache.

H. influenzae can also cause bacterial meningitis and infections of the bloodstream.

Chlamydia (Chlamydia trachomatis)

C. trachomatis is a Gram-negative coccobacillus that causes chlamydia, one of the most frequently reported sexually transmitted infections in the United States.

While it usually doesn’t cause symptoms in men, women might experience unusual vaginal discharge, bleeding, or painful urination.

If left untreated, chlamydia can lead to infertility in both men and women. It can also increase a woman’s risk for developing pelvic inflammatory disease.

Periodontitis (Aggregatibacter actinomycetemcomitans)

Periodontitis is a gum infection that damages your gums and the bone that supports your teeth. Untreated periodontitis can cause loose teeth and even tooth loss.

A. actinomycetemcomitans is a Gram-negative coccobacillus that can cause aggressive periodontitis. Although considered normal flora of the mouth that can spread from person to person, it’s often found in young people with periodontitis.

Symptoms of periodontitis include swollen gums, red or purple gums, bleeding gums, bad breath, and pain when chewing.

A. actinomycetemcomitans can also cause urinary tract infections, endocarditis, and abscesses.

Whooping cough (Bordetella pertussis)

Whooping cough is a serious bacterial infection that’s caused by the Gram-negative coccobacillus B. pertussis.

Early symptoms include a low fever, runny nose, and cough. In infants, it can also cause apnea, which is a pause in breathing. Later symptoms often involve vomiting, exhaustion, and a distinctive cough with a high-pitched “whoop” sound.

Plague (Yersinia pestis)

Plague is caused by the Gram-negative coccobacillus Y. pestis.

Historically, Y. pestis caused some of the most devastating outbreaks in history, including the “black plague” of the 14th century. While it’s rarer today, cased do still occur. According to the World Health Organization, there were more than 3,000 cases of plague reported between 2010 and 2015, causing 584 deaths.

Symptoms of plague can include a sudden fever, chills, headache, aches and pains throughout your body, a feeling of weakness, nausea, and vomiting.

Brucellosis (Brucella species)

Brucellosis is a disease caused by Gram-negative coccobacilli from the genus Brucella. It’s usually found in animals, such as sheep, cattle, and goats. However, humans can get it from eating or drinking unpasteurized dairy products.

The bacteria can also enter your body through cuts and scratches or through mucus membranes.

Symptoms of brucellosis include headache, feelings of weakness, fever, sweating, chills, and body aches.

Coccobacilli are responsible for many conditions that cause a variety of symptoms, so treatment often depends on the type of illness you have.


The first step in treating coccobacilli-related infections is taking antibiotics. Your doctor will prescribe one that’s most likely to target the specific coccobacillus that’s causing your symptoms. Make sure you take the full course that’s prescribed by your doctor, even if you start to feel better before finishing it.


Whooping cough and plague are both much less common today than they used to be, thanks to vaccines against B. pertussis and Y. pestis.

The Centers for Disease Control and Prevention recommends that all babies, children, preteens, teenagers, and pregnant women be vaccinated against whooping cough.

The H. influenzae vaccine only protects against diseases caused by H. influenzae type b. However, now fewer than 50 cases of H. influenzae type b disease occur annually in younger children in the United States compared to 1,000 deaths each year prior to introduction of the vaccine.

The World Health Organization recommends getting vaccinated against Y. pestis only if you have a high risk of coming into contact with it. For example, people who work in laboratories have a higher risk of encountering more rare types of bacteria.

While coccobacilli bacteria don’t always cause illness, they’re responsible for some human diseases, ranging from mild to severe. If you’re diagnosed with a coccobacilli infection, your doctor will likely prescribe antibiotics to kill off the bacteria.