Streptococcus pneumoniae


00:00 / 00:00



Streptococcus pneumoniae


Introduction to bacteria

Bacterial structure and functions

Gram positive bacteria

Staphylococcus epidermidis

Staphylococcus aureus

Staphylococcus saprophyticus

Streptococcus viridans

Streptococcus pneumoniae

Streptococcus pyogenes (Group A Strep)

Streptococcus agalactiae (Group B Strep)


Clostridium perfringens

Clostridium botulinum (Botulism)

Clostridium difficile (Pseudomembranous colitis)

Clostridium tetani (Tetanus)

Bacillus cereus (Food poisoning)

Listeria monocytogenes

Corynebacterium diphtheriae (Diphtheria)

Bacillus anthracis (Anthrax)


Actinomyces israelii

Gram negative bacteria

Escherichia coli

Salmonella (non-typhoidal)

Salmonella typhi (typhoid fever)

Pseudomonas aeruginosa


Klebsiella pneumoniae


Proteus mirabilis

Yersinia enterocolitica

Legionella pneumophila (Legionnaires disease and Pontiac fever)

Serratia marcescens

Bacteroides fragilis

Yersinia pestis (Plague)

Vibrio cholerae (Cholera)

Helicobacter pylori

Campylobacter jejuni

Neisseria meningitidis

Neisseria gonorrhoeae

Moraxella catarrhalis

Francisella tularensis (Tularemia)

Bordetella pertussis (Pertussis/Whooping cough)


Haemophilus influenzae

Haemophilus ducreyi (Chancroid)

Pasteurella multocida


Mycobacterium tuberculosis (Tuberculosis)

Mycobacterium leprae

Mycobacterium avium complex (NORD)

Other bacteria

Mycoplasma pneumoniae

Chlamydia pneumoniae

Chlamydia trachomatis

Borrelia burgdorferi (Lyme disease)

Borrelia species (Relapsing fever)


Treponema pallidum (Syphilis)

Rickettsia rickettsii (Rocky Mountain spotted fever) and other Rickettsia species

Coxiella burnetii (Q fever)

Ehrlichia and Anaplasma

Gardnerella vaginalis (Bacterial vaginosis)


Streptococcus pneumoniae


0 / 39 complete

USMLE® Step 1 questions

0 / 5 complete

High Yield Notes

6 pages


Streptococcus pneumoniae

of complete


USMLE® Step 1 style questions USMLE

of complete

A 34-year-old man presents to his primary care physician for evaluation of sinus pressure. The patient has had a stuffy nose with purulent nasal discharge for the past two weeks. In addition, he has been experiencing headaches and ear fullness. His symptoms began improving around 11-12 days after onset but then took a turn for the worse. Past medical history is notable for type II diabetes mellitus, for which he takes metformin daily. Temperature is 38.9°C (102°F), pulse is 101/min, respirations are 19/min, and blood pressure is 132/71 mmHg. Physical exam demonstrates tenderness to palpation over the bilateral maxillary sinuses. Which of the following organisms is the most likely cause of this patient’s clinical presentation?

External References

First Aid









Streptococcus pneumoniae p. , 134

Otitis media

Streptococcus pneumoniae p. , 134

Pneumonia p. 707

Streptococcus pneumoniae p. , 134

Streptococcus pneumoniae p. , 134

α-hemolysis p. 133

bacterial meningitis p. 727

chloramphenicol p. 189

cystic fibrosis p. 176

encapsulated bacteria p. 125

Gram-positive testing p. 132

IgA protease and p. 127

immunodeficient patients p. 116

influenza p. 166

IV drug use and p. 177

meningitis p. 177

penicillin G/V for p. 184

pneumonia p. 176, NaN

postviral infection p. 176

splenic dysfunction p. 96

transformation in p. 128

Virulence factors

Streptococcus pneumoniae p. , 134


Content Reviewers

Rishi Desai, MD, MPH

Filip Vasiljević, MD


Evan Debevec-McKenney

Elizabeth Nixon-Shapiro, MSMI, CMI

Robyn Hughes, MScBMC

Evode Iradufasha, MD

Jake Ryan

Streptococcus pneumoniae or Strep. pneumoniae can be broken down into strepto- which means chain, -coccus, which means round shape, and pneumoniae, which refers to the fact that it causes pneumonia - no surprises there.

So, Strep pneumoniae are round bacteria that tend to grow in chains, usually in lancet-looking pairs called diplococci.

They’re the most common cause of community-acquired pneumonia - meaning pneumonia acquired somewhere other than the hospital.

Ok now, a little bit of microbe anatomy and physiology.

Strep pneumoniae has a thick peptidoglycan cell wall, which takes in purple dye when Gram stained - so this is a gram-positive bacteria.

They’re non-motile and don’t form spores, and also, they’re facultative anaerobes, meaning that they can survive in both aerobic and anaerobic environments.

Finally, they’re catalase negative - which means they don’t produce an enzyme called catalase.

Ok, now, when cultivated on a medium called blood agar, Strep pneumoniae colonies cause alpha hemolysis, also called green hemolysis, because they produce hydrogen peroxide, which partially oxidizes initially red hemoglobin in the blood agar to green methemoglobin.

Other Streptococcus species, like Strep viridans, are also alpha hemolytic.

So, an optochin test is done to distinguish Strep pneumoniae. That’s where a few drops of optochin are added to the culture.

Strep pneumoniae are optochin sensitive, meaning the bacteria dies after adding optochin, whereas Strep viridans are optochin resistant - meaning they survive.

Now, Strep pneumoniae has a number of virulence factors, that are like assault weaponry that help it attack and destroy the host cells, and evade the immune system.

So first, Strep pneumoniae is encapsulated, meaning it’s covered by a polysaccharide layer called a capsule.

The capsule has pili and fimbriae, which are hair-like extensions that help it attach to a host cell.

Once attached to a mucosal surface like in the nasopharynx or the middle ear, Strep pneumoniae can multiply and produce biofilms.


Streptococcus pneumoniae, or pneumococcus, is an encapsulated, gram-positive, and catalase-negative bacterium. It is found asymptomatically colonizing the nasal cavities and sinuses, but they can take advantage of a weakened immune system, especially in very young or very old individuals, or in those with diabetes, HIV infection, cancer, splenectomy, or those with sickle cell disease.

Streptococcus pneumoniae can cause diseases such as rhinosinusitis, otitis media, pneumonia, and meningitis. Symptoms vary depending on the type but can include fever, chills, coughing, chest pain, and difficulty breathing. The treatment of infection with Strep pneumoniae involves the use of Penicillins, but in the case of resistant strains, fluoroquinolones, third-generation cephalosporins, and vancomycin can be used.


Copyright © 2023 Elsevier, except certain content provided by third parties

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.