Characteristics of Streptococcus Pneumoniae

According to George Brooks, M.D., Professor of Laboratory Medicine and Microbiology and Immunology at the University of California, Streptococcus pneumoniae is normally found in 5 to 40 percent of the population. It has mechanisms ready and waiting to be used to cause disease.

What is it?

Streptococcus pneumoniae is a gram positive diplococci bacterium. Bacteria can be classified by microbiologists with the use of a staining process called a Gram stain. Streptococcus pneumoniae is gram positive because it keeps the first stain that is used in the Gram stain process. It is called diplococci because it is round (cocci) and arranged in twos.

How Does it Cause Disease?

The main reason why Streptococcus pneumoniae can cause disease is because it has a capsule that surrounds it and protects it from your immune system. In addition to the capsule, it has an enzyme called IgA1 protease. You have antibodies called IgA that defend your respiratory system against foreign substances; IgA is in the mucous membrane that lines your respiratory system. Streptococcus pneumoniae uses the IgA1 protease to destroy your IgA antibodies, so it can live in the mucous membrane of your upper respiratory system. It also has a substance called pneumolysin O that damages your respiratory lining. It will then multiply.

Who is Susceptible to Infection?

Dr. Brooks writes in “Jawetz, Melnick, & Adelberg’s Medical Microbiology,” that since so many people have Streptococcus pneumoniae in their respiratory tracts but are not sick, their immune systems must be working. This also means if you get sick, something has made you susceptible to be infected. Such factors include alcoholism, illegal drugs, viral infections, heart failure, malnutrition and sickle cell anemia.

What Diseases Does it Cause?

The diseases caused by Streptococcus pneumoniae include otitis media (the inflammation of your middle ear), sinusitis (the inflammation of your sinuses) and bronchitis (the inflammation of your bronchi). It also causes meningitis. According to John Bartlett, M.D., Professor of Medicine at John Hopkins University School of Medicine, bacteria is the main organism that causes pneumonia if you are over the age of 30. Streptococcus pneumoniae is the most common bacteria to cause it.


Otitis media is usually contracted by children. They may have a fever, be irritable and pull on the affected ear. Sinusitis can cause fever, nasal congestion, headache and pain around your upper teeth. With bronchitis, you may have cough and difficulty breathing. Pneumonia usually causes sudden chills, fever, sharp pain, difficulty breathing and cough. You will also spit up phlegm, called sputum, which will have a rusty color. Meningitis causes fever, chills, headache and mental confusion.

About this Author

Based in North Carolina, Ruth Coleman has written articles and manuals for 25 years. Her writing has appeared in community newspapers, places of employment and comprises work done in medical college, of which she is a recent graduate. Ruth Coleman holds a Bachelor of Science in biology from Salem College, and is the recipient of numerous academic awards.