The pathogenesis of Streptococcus pneumoniae

Published: Last Edited:


Streptococcus pneumoniae 1

Bacteria are everywhere, most are harmless and can live on your skin and inside your body without you even knowing. Bacteria can be very beneficial. They have been used to make every day items and medications such as antibiotics, enzymes, alcohols, amino acids, and vitamins. Some bacteria however can become harmful and cause diseases, making them pathogens. Pathogens are like parasites, they need a host to live in or on and take what they need from their host to survive. They do damage to their host by causing infection and disease (Talaro & Chess, 2012).

One pathogenic bacteria in particular is Streptococcus pneumoniae. It was discovered by Louis Pasteur in 1881 (Kelly). This is one of those bacteria that can live inside your body already, mainly in the nasopharynx, and most of the time it isn’t doing any harm and you don’t even know you have it. About 5% to 50% of people already carry the S. pneumoniae as a part of their normal flora in their body. However S. pneumoniae can become very dangerous and cause a few different diseases. The main ones that will be discussed in this paper are bacterial pneumonias, meningitis, and ear infections (Talaro & Chess, 2012).

There are certain predisposing complications that can put a person at high risk for getting a pneumococcal disease. Cardiac and pulmonary impairments such as, heart failure, liver failure, or asthma can put one at higher risk. Smoking is a big risk factor. Also having a disease or taking certain drugs that lower the immune system will cause a person to have a greater risk of getting a pneumococcal disease (“Pneumococcal disease”, 2012).

This bacteria is transmitted by coming in contact with the respiratory secretions or droplets of a person who is already infected. The person can transmit the disease for as long as the organism appears in their respiratory tract (“Pneumococcal disease”, 2012). The drug of choice to treat this pathogen is penicillin. However, some people cannot have penicillin due to allergies or the bacteria is resistant to it. Therefore it can also be treated with other drugs such as cephalosporins, erythromycin, quinolones, and sulfonamides.

These diseases can also be prevented with the proper vaccines. The first development of the pneumococcal vaccine began in 1911. However penicillin was developed in the 1940s, so this made people less interested in getting the vaccine and more interested in only being treated with penicillin. However people began dying despite the use of penicillin, indicating this bacteria may be becoming resistant to penicillin. So by the late 1960s they began developing the vaccine once again (“Pneumococcal disease”, 2012).

Pneumovax is vaccine that is typically given to older patients and those who are at high risk for other diseases such as congestive heart failure, diabetes, and lung disease. This vaccine should be given every five years. Prevnar and Prevnar13 are given to young children to prevent meningitis and ear infections (Talaro & Chess, 2012).

This bacteria has hospitalized an estimated 175,000 people each year in the United States. This pathogen isn’t just contained in the United States though, it is estimated that this has caused 14.5 million illnesses worldwide. With 735,000 reported deaths worldwide from diseases caused by S. pneumoniae. In some countries such as, sub-Saharan African, Uganda, and Kenya, the death toll is high due to lack of availability of the pneumococcal vaccine. This bacteria is a very big cause of deaths worldwide (Kelly).

Pneumonia occurs when the S. pneumoniae bacteria is aspirated into the lungs and causes infection. Inflammation of the alveoli, the air sacs of the lungs, occurs and they fill with fluid. This causes the lungs to not be able to take in oxygen or remove carbon dioxide efficiently, which can make it difficult to breathe, also known as dyspnea (Shiffman, 2015). This can also cause increased amounts of carbon dioxide in the blood which can put a person into respiratory acidosis.

There are two different types of pneumococcal pneumonia, lobar and bronchial. The bronchial type involves the alveoli and lager bronchioles and is most commonly found in infants, children, and elderly people. The lobar type involves a single lobe and the entire area becomes a mass. The lobar pneumonia is most commonly found in young adults (Todar, 2012).

Pneumococcal pneumonia has an incubation period of 1-3 days (“Pneumococcal disease”, 2012). This means that it can take 1-3 days from the time you are infected until you have any signs and symptoms. Some signs and symptoms of pneumococcal pneumonia include severe chest pain, fever, chills, shaking, rapid abnormal breathing, difficulty breathing, a productive cough, weakness, fast heart rate, bloody sputum, and cyanosis which is a blueish color of the skin due to decrease in oxygen. Nausea, vomiting, and headaches can occur but they are less common with pneumonia. Complications of pneumococcal pneumonia include pericarditis, empyema, atelectasis, lung abscess, and endobronchial obstruction (“Pneumococcal disease”, 2012).

S. pneumoniae can gain access to the Eustachian tube and cause otitis media (a middle ear infection). This occurs mainly in children under 2 years old because their Eustachian tubes are much shorter than an older person. S. pneumoniae causes inflammation of the middle ear which causes ear pain and can lead to possible temporary deafness (Talaro & Chess, 2012).

One fourth of people who have pneumonia also have meningitis. Symptoms of meningitis may include fever, vomiting, headache, irritability, lethargy, nuchal rigidity, seizure, cranial nerve sign, and even coma. The fatality rate with meningitis is about 30% but in elderly people it can be as high as 80%. Those who do survive this disease may have neurological impairments (“Pneumococcal disease”, 2012).

S. pneumoniae is a part of the viridans group, and one of the most serious complications of streptococcal infections is subacute endocarditis, which is infection and inflammation of the lining of the heart. Colonies of this bacteria start to form a biofilm called vegetation. This vegetation gets larger and starts to release amounts of bacteria into the circulatory system. These masses of bacteria form into clots, or emboli, and can travel to the lungs and brain and block off circulation which causes severe damage to the organs (Talaro & Chess, 2012).

In order to even diagnose a pneumococcal infection you must collect a specimen. This can be either a sputum sample, spinal or pleural fluid, or blood cultures. S. pneumoniae is a fastidious bacteria, meaning it has to have certain nutritional requirements and therefore must be cultured on a blood agar. Blood agars contain animal blood that can provide the bacteria with the nutrients needed. With these two things a gram stain can be done to help diagnose (Talaro & Chess, 2012).

Gram staining, which was invented by Hans Christian Gram over 130 years ago, is a way of using dyes on the bacteria to distinguish different characteristics and help to diagnose which type of bacteria it is. Right away you can tell whether the bacteria is going to be positive if it stains purple or negative if is stains red. Gram staining can also help to show the arrangement of the cells and their size and shape (Talaro & Chess, 2012).

S. pneumoniae is a gram positive bacteria, which means it can be easier to get rid of and would show up purple under a microscope. It is considered a facultative anaerobe, meaning that it does not need oxygen to survive but it can still live in its presence. It grows the best in the presence of 5% to 10% of carbon dioxide. This bacteria is sensitive and won’t live very long outside of its habitat.

S. pneumoniae has the ability to self-destruct due to autolysin. Autolysin is an enzyme that digests the cell wall (Kelly). If the bacteria is grown to the stationary phase in a lab, it will undergo lysis after about 18-24 hours. The colonies may start to appear plateau-typed but as autolysis begins they will collapse in the middle. The whole colony will be destroyed (Todar, 2012).

These microscopic cells would show up as lancet shaped and would be in pairs called diplococci and short chains (Talaro & Chess, 2012). Each cell is 0.5 to 1.25 micrometers in diameter. They don’t contain the enzyme catalase, which would break down hydrogen peroxide. They do however ferment glucose which is sugar, into lactic acid (Todar, 2012).

Most strains of S. pneumoniae are encapsulated which makes them pathogenic to humans. They will appear to be smooth if the bacterial cells are encapsulated. If they appear to be rough then they are not encapsulated and are nonvirulent (Talaro & Chess, 2012). These capsules are made up of polysaccharides. A polysaccharide is a carbohydrate molecule that is made up of sugar.

They also protect the cells against phagocytosis. Phagocytosis means the cells are trying to be devoured by leukocytes. Leukocytes are white blood cells that fight to attack infectious diseases. However they can’t be because of their protective capsules which makes this bacteria virulent and difficult to get rid of (Todar, 2012). These organisms will not be found in animals or insects. There have been 90 different stereotypes identified, which is why this bacteria can be so hard to treat (“Pneumococcal disease”, 2012).

A way to distinguish between stereotypes is by use of the quellung reaction. The bacteria is mixed with a specific antiserum and then observed under a micro scope at 1000X total magnification. They are looking for capsular swelling to determine specific capsular types (Todar, 2012).

The S. pneumoniae cells are not motile and don’t form spores. Their cell walls are about six layers thick and are made up of peptidoglycan with teichoic acid (Todar, 2012). According to Talaro and Chess (2012), a peptidoglycan is a polysaccharide that is combined with peptide fragments to provide support for the structure of the cell wall. The teichoic acid provides maintenance and enlargement for the cell during division.

The S. pneumonia cells have hair like structures on them that are called pili. These are cause colonies in the upper respiratory tract and nasopharynx (Todar, 2012). Pili are considered appendages and make it so the cells can interact with one another (Talaro & Chess, 2012). This is why the pili are responsible for forming colonization.

There is a specific way to classify and name living things, it’s called taxonomy and was created by Carl von Linne. It starts with domain which is based on the cell type; it will be one of three, eukaryote, bacteria, or archaea. Next comes the kingdom, which is then divided into phylum. Then it is divided even further into class, order, family, genus, and finally species (Talaro & Chess, 2012).

S. pneumonia falls in to the bacteria domain. It belongs to the phylum Firmicutes, and the class Bacilli. The order is Lactobacillales, the family is Streptococcaceae, the genus and species are Streptococcus pneumonia (Kelly). When you look at the classification as a whole it reads Bacteria Firmicutes Bacilli Lactobacillales Streptococcaceae Strepococcus pneumoniae.

In conclusion S. pneumoniae is a gram positive, lancet shaped diplococci, that is arranged in short chains. It is part of the normal flora in 5% to 50% of the population and usually does no harm to the body. If it is aspirated into the lungs or one comes in direct contact with another infected person’s droplets then it can cause infection. This pathogen causes bacterial pneumonia, meningitis, and ear infections among other types of infections.

There are 90 different strains and some are encapsulated making them virulent and harder to get rid of. The best way to treat pneumococcal disease is with penicillin, however some are resistant to this antibiotic. Getting a pneumococcal vaccine can help prevent pneumococcal infections. One of the best preventions of infection, that requires little effort, is washing your hands.


Kelly, C. Pneumococcal disease. Retrieved from

(2012) Pneumococcal disease. The pink book. Retrieved from

Schiffman, G. (2015). Bacterial pneumonia. Retrieved from

Talaro, K.P., & Chess, B. (2012). Foundations in microbiology (8th ed.). United States of America: The McGraw-Hill Companies, Inc.

Todar, K. (2012). Todar’s online textbook of bacteriology (Streptococcus pneumonia). Retrieved