Streptococcus pneumoniae

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Streptococcus pneumoniae



Streptococcus pneumoniae


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Streptococcus pneumoniae

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A 65-year-old man comes to the emergency department for evaluation of three days of dyspnea, fever, and cough. Past medical history is significant for gastroesophageal reflux disease, dyslipidemia, HIV, and two episodes of Pneumocystis carinii pneumonia. The patient is compliant with antiretroviral therapy and his last CD4 count was 250 cells/microL. Current medications include tenofovir-emtricitabine and dolutegravir, atorvastatin, and aspirin. The patient is sexually active with men and women and uses condoms consistently. The patient does not use intravenous drugs, alcohol, or tobacco. The patient owns two parrots and a cat. Temperature is 38.11°C (100.0°F), pulse is 100/min, respirations are 20/min, and blood pressure is 130/75 mmHg, SpO2 is 92% on room air. Physical examination reveals anterior and posterior cervical lymphadenopathy as well as rales over the right anterior and posterior chest. A Chest x-ray is depicted below. Which of the following is the most likely organism implicated in this patient's current clinical condition?

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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


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.


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