Streptococcus Pneumoniae Bacteria and Pneumococcal Diseases
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 pneumococcus. Diseases caused by the bacterium are known as pneumococcal diseases or infections. The prefix "pneumo" refers to the lungs. Unfortunately, the bacterium sometimes travels beyond the respiratory system and causes problems in the heart, brain, or other parts of the body.
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 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, S. pneumoniae 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)
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 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 S. pneumoniae into our body. Until recently, it was thought that the bacterium 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 S. pneumoniae has a good ability to survive desiccation and remain infective.
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.
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. Invasive infections caused by S. pneumoniae include meningitis, endocarditis, and bacteremia. Bacteremia can lead to sepsis or blood poisoning.
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.
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.
Structure and Function of the Ear
S. pneumonia 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.
Otitis Media in Children and Adults
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.
The main symptom of AOM is pain caused by the pressure of middle ear fluid on the eardrum. There may also be partial hearing loss and a fever.
Anyone with symptoms that are unexplained or that suggest the presence of a pneumococcal disease should visit a doctor. The doctor will provide a diagnosis and treatment for the patient's specific condition. A doctor can also give advice about ways to prevent pneumococcal diseases in the future.
The meninges are three membranes that surround the brain and spinal cord. The outer membrane is known as the dura mater, the middle one is the arachnoid, and the inner one is the pia mater.
Meningitis is an inflammation of the membranes covering the brain or spinal cord. The membranes are collectively known as the meninges. Symptoms of meningitis include a headache, a stiff neck, nausea, vomiting, and a fever. Meningitis can be dangerous because swelling of the meninges during inflammation can put pressure on the brain.
Meningitis is caused by both bacteria and viruses. Most cases are caused by viruses, but some result from a bacterial infection. Bacterial meningitis is more likely to be life-threatening and can be very serious. S. pneumoniae is the most common cause of bacterial meningitis.
Bacteria may reach the meninges after entering the bloodstream. They may sometimes reach the meninges during another health problem, such as an ear infection or a fractured skull. Treatment often involves antibiotics to kill bacteria and corticosteroids to prevent swelling. Viral meningitis may require treatment, but it sometimes disappears on its own. It's always necessary to see a doctor about a possible case of meningitis, however.
The heart contains chambers that fill with blood. The wall of the heart is made of muscle, or myocardium, which contracts to push the blood to where it's needed. A double-walled membranous sac called the pericardium covers the outside of the heart muscle and a membrane known as the endocardium lines the inside.
Endocarditis is inflammation of the endocardium. The inflammation is generally caused by a bacterial infection. The bacteria come from another part of the body, especially the mouth, and reach the heart via the bloodstream. S. pneumoniae is one cause of endocarditis, but there are other bacteria that also cause the disease.
Bacteria may enter a person's bloodstream as a result of the following processes.
- Chewing food, brushing the teeth, and flossing (especially when the gums are unhealthy)
- Undergoing dental surgery in which the gums are cut
- Experiencing damage to the intestinal lining
- Receiving a skin piercing with a needle
- Experiencing an injury to the skin that leaves a sore
Endocarditis is a potentially serious condition because it may damage the valves inside the heart. The valves prevent blood from flowing backwards as the heart beats. This is an essential process in order for blood to leave the heart. Valve damage is more likely if the valves have been weakened by another cause. Endocarditis is usually treated with antibiotics and sometimes with surgery.
What Is Sepsis?
Bacteremia and Sepsis or Blood Poisoning
Bacteremia is a condition in which bacteria are present in the blood. Temporary bacteremia caused by activities such as brushing the teeth may not be a problem, but the disorder can be serious. Bacteria that stay in the blood can be transferred to different organs and tissues in the body and may trigger sepsis.
Sepsis arises due to an excessively strong reaction of the immune system to harmful items in the blood, such as bacterial cells or the toxins that they produce. The condition is sometimes referred to as blood poisoning by the general public. The blood is flooded by chemicals designed to fight the bacteria. These chemicals cause inflammation throughout the body and trigger reactions that damage multiple organs. Sepsis may lead to septic shock, a condition that involves dangerously low blood pressure.
Sepsis is a very serious condition that is life threatening and requires a hospital visit. Antibiotics, intravenous fluids, and procedures to protect organs are generally part of the treatment. The sooner the treatment begins, the better.
The inflammatory response is a normal part of the immune system's activities as it fights invaders and damage. It's usually a temporary and helpful action that occurs in a limited area of the body. The excessive and widespread inflammation that occurs during sepsis is dangerous, however.
Treating and Preventing Pneumococcal Diseases
Antibiotics are generally the main treatment for pneumococcal infections. Additional treatments specific to the condition of the patient or the particular part of the body that is affected may also be used.
It's best to prevent pneumococcal diseases if we can. Since there is some uncertainty about the length of time that S. pneumoniae can survive outside the body, it's important to wash our hands frequently and to avoid touching our eyes, nose, and mouth as much as possible. These steps are helpful for avoiding any type of bacterial infection. Avoiding close contact with people who are sick would also be helpful, although it's not always possible to do this. Following a healthy diet and exercising regularly will help to keep our immune system working effectively.
A vaccine is available to prevent pneumococcal diseases. The bacterium exists in slightly different forms known as serotypes. A pneumococcal vaccine protects against the most common serotypes in an area, but it doesn't protect against all of them. Doctors often recommend that people with certain health problems or in certain life stages receive the vaccine, however. As more research is performed, we may have other ways to protect ourselves from the sometimes annoying and occasionally dangerous S. pneumoniae bacterium.
- "Pneumococcal Disease." Centers for Disease Control and Prevention. https://www.cdc.gov/vaccines/pubs/pinkbook/pneumo.html (accessed September 15, 2017).
- Pneumococca infections. Medscape. http://emedicine.medscape.com/article/225811-overview (accessed September 15, 2017).
- Invasive Pneumoccal Disease. Public Health Agency of Canada. https://www.canada.ca/en/public-health/services/immunization/vaccine-preventable-diseases/invasive-pneumococcal-disease.html (accessed September 15, 2017).
© 2016 Linda Crampton