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Streptococcus pneumoniae and Pneumococcal Disease Facts

Linda Crampton is a writer and former teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

Streptococcus pneumoniae lives in our nasal cavity and nasopharynx.

Streptococcus pneumoniae lives in our nasal cavity and nasopharynx.

What Are Pneumococcal Diseases?

Streptococcus pneumoniae is a bacterium that lives in the human nose. It may sound like a dangerous creature because of its name. The bacterium can certainly cause some unpleasant and even life-threatening diseases, including pneumonia. It often lives harmlessly in and around the nose without producing any symptoms, however.

S. pneumoniae (as it's often called) is also known as a pneumococcus. A coccus is a bacterium with round cells. The plural form is cocci. Diseases caused by S. pneumoniae are known as pneumococcal diseases or infections. These terms are sometimes used in the singular. Each name then represents a range of disorders caused by the bacterium.

The prefix "pneumo" refers to the lungs. Unfortunately, the bacterium sometimes travels beyond the respiratory system and may cause problems in the heart, brain, or other parts of the body.

S. pneumoniae often exists as pairs of bacteria known as diplococci. The green coloration in this photo is artificial.

S. pneumoniae often exists as pairs of bacteria known as diplococci. The green coloration in this photo is artificial.

The scientific name of an organism consists of the genus and the species. One convention in science is that when a scientific name has been written once in an article, subsequent references to the organism may abbreviate the genus. I've followed this convention.

Streptococcus pneumoniae

Streptococcus is a genus of microscopic, single-celled bacteria. The individual cells often join to form pairs and are sometimes found in chains. Each cell is surrounded by a protective capsule. S. pneumoniae was discovered in 1881 by Louis Pasteur. Pasteur was a French microbiologist and chemist who is famous for his discoveries of methods to prevent disease. He invented the process of pasteurization, which is named in his honour.

As is the case for other bacteria, researchers are discovering that S. pneumoniae is far more complex than was originally realized. It produces a variety of chemicals to help it adhere to cells in different parts of our body and to penetrate them when it becomes invasive. It also forms biofilms, which are layers of bacteria attached to a surface and covered by a protective polysaccharide coating. Bacteria in biofilms send chemical messages to each other and coordinate their behaviour. Like some other bacteria that have been studied, pneumococcus cells sometimes exchange genes with their neighbours. This means that they can change their characteristics during their lifetime.

Pneumococci are common inhabitants of the respiratory tract and may be isolated from the nasopharynx of 5% to 90% of healthy persons. Rates of asymptomatic carriage vary with age, environment, and the presence of upper respiratory infections.

— CDC (Centers for Disease Control and Prevention)

Coughs and sneezes can spread diseases. This photo of a baby who is about to sneeze was taken at just the right moment.

Coughs and sneezes can spread diseases. This photo of a baby who is about to sneeze was taken at just the right moment.

The information below is given for general interest. Anyone with major symptoms of ill health or with ones that persist or are recurrent should visit a doctor for a diagnosis. The doctor will be able to answer a patient’s questions about Streptococcus pneumoniae.

Transmission of Streptococcus pneumoniae

S. pneumoniae is transmitted in microaerosol form. When we sneeze, cough, or even talk, we release tiny droplets of liquid from our nose and throat. These droplets contain bacteria and are inhaled by other people. Close contact increases the risk that potentially dangerous species will be inhaled and that the bacteria will be inhaled in sufficient quantity to hurt people.

Touching objects recently contaminated by bacteria, including eating and drinking utensils, and then touching our nose or mouth can also transfer microbes into our body. Until recently, it was thought that S. pneumoniae didn't live long outside the body and that cells dropped on surfaces would soon die. Recent research has called this assumption into doubt. Tests have shown that the species has a good ability to survive desiccation and remain infective.

A view of Streptococuus pneumoniae at higher magnification

A view of Streptococuus pneumoniae at higher magnification

Invasive Bacterial Infections

Our immune system can often destroy bacteria that enter our body or at least restrict their spread, but this isn't always the case. Bacteria sometimes move beyond their infection area.

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S. pneumoniae may travel away from the nasopharynx through passageways and cause conditions such as pneumonia and otitis media. It may also travel beyond the respiratory system via the bloodstream. If bacteria in the blood aren't destroyed by the immune system, they are said to be invasive. Infections that may be caused by invasive pneumococci include meningitis and endocarditis. Bacteria in the bloodstream may trigger sepsis.

People whose immune system isn't working at full effectiveness are most likely to experience an invasive infection. These people include children younger than 5, people aged 65 or older, people suffering from an HIV infection, cancer, or diabetes, and people receiving immunosuppressive drugs after an organ transplant. The people in these categories won't necessarily experience an invasive infection when S. pneumoniae is present, but the probability is increased.

Someone with pneumonia may not have all of the symptoms shown in the illustration above. "Pleuritic chest pain" refers to pain caused by inflammation of the membranes surrounding the lungs. "Hemoptysis" means coughing up blood.


Pneumonia is a disease in which the air sacs in the lungs are inflamed. As a result of the inflammation, the sacs fill with fluid, which makes breathing difficult. The inflammation is caused by the presence of bacteria, viruses, fungi, or parasites. Pneumonia ranges from a mild to a very serious condition. S. pneumoniae is the most common cause of community-acquired pneumonia in North America and Europe.

People with certain pre-existing disorders are more susceptible to pneumonia than healthy people. The disorders include asthma, chronic bronchitis, and COPD (chronic obstructive pulmonary disease). People with these health problems may not be able to empty their lungs sufficiently during exhalation, which increases the risk of pneumonia.

The ear during a case of otitis media

The ear during a case of otitis media

Structure and Function of the Ear

S. pneumoniae sometimes contributes to an ear condition called otitis media. A disorder whose name ends in "itis" involves inflammation. In the case of otitis media, the middle ear is inflamed. The term "middle ear" has a specific meaning in human anatomy. Our ears consist of more than what is visible on the sides of our head.

  • The outer or external ear consists of the visible pinna and the ear canal inside the skull. Sound vibrations travel along the canal and hit the eardrum (or the tympanic membrane) at the end.
  • The middle ear is located behind the eardrum and is filled with air. It contains three tiny bones called ossicles that transmit sound vibrations.
  • The inner or internal ear contains the hearing organ or cochlea. It responds to sound vibrations by sending a signal along the auditory nerve to the brain. The inner ear also contains the semicircular canals, which are responsible for our sense of balance.

Acute Otitis Media or AOM

A channel called the Eustachian tube (or the auditory tube) connects the middle ear to the nasopharynx behind the nose. The main function of the tube is to equalize the air pressure in the middle ear and the atmosphere. It also allows for the drainage of secretions and debris that collect in the middle ear. The tube opens and closes as necessary.

Acute otitis media, or AOM, generally follows an upper respiratory tract infection. The development of AOM isn't fully understood. The middle ear and the Eustachian tube are lined with the same type of tissue that lines the nasal cavity and are thought to respond in the same way during an upper respiratory tract infection. Fluid is released from the inflamed and swollen lining of the middle ear. The Eustachian tube becomes blocked or narrowed when its lining becomes inflamed and swollen.

The narrowed Eustachian tube is unable to function properly. As a result, bacteria and viruses in the nasopharynx may travel through the Eustachian tube into the middle ear, resulting in a secondary infection and making conditions even worse. The bacteria are very often S. pneumoniae, although other bacteria may be present in addition to or instead of the pneumococcus.