What Organism Is Causing this Pneumonia?

Session 35

Infectious Disease! A young man presents with increasing SOB and green sputum. Sputum culture shows α-hemolytic gram-positive cocci in chains. Name that bug! We’re joined by Dr. Mike Natter from BoardVitals. Find him on Instagram @mike.natter.

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[04:45] Question of the Week:

A 35-year-old man presents to his primary care physician a three-day history of increasing shortness of breath and a productive cough with green sputum. He has no significant past medical history.

Physical exam reveals decreased breath sounds and dullness to percussion in the right lower lung field. A sputum sample is obtained and sent for gram staining. It demonstrates large numbers of gram-positive cocci in chains.

When these cells are cultured on a blood agar plate, an alpha-hemolytic reaction is observed. Based on these microbiology results, which of the following is the most likely diagnosis:

(A) Haemophilus influenza pneumonia

(B) Klebsiella pneumonia

(D) Streptococcus agalactiae pneumonia

(E) Streptococcus pneumoniae

[08:26] Thought Process Behind the Correct Answer

A 35-year-old guy with no medical history then has picked this in the community. He’s immunocompromised, not a child, and all these other things. It means he’s going to likely pick up the most common form of pneumonia in the community which is Streptococcus pneumoniae.

From a micro standpoint, there are two things to think about Streptococcus pneumoniae. They’re gram-positive cocci in chains. And on the blood agar, it’s going to be alpha-hemolytic. Look for ways to tap this into your memory. Draw a picture or create an affiliation. Think of s story.

'However you want to find a way to tap that into your memory – draw a picture, create an affiliation, think of a story – those things are definitely worth memorizing for test purposes.'Click To Tweet

[09:44] Understanding the Other Answer Choices

With Haemophilus influenza pneumonia, think of a young kid with inner ear infections. These are typically going to be seen in young kids or immunocompromised patients.

Klebsiella pneumonia is seen on immunocompromised folks. It’s characterized by currant jelly sputum.

Staphylococcus aureus pneumonia is really bad. This is not someone who’s just going to be strolling around. You can get real sick with this. It’s gram-positive. It’s a bacillus, not a cocci. This is going to help you differentiate this from Strep.

Streptococcus agalactiae is what neonates get as they pass through the birth canal. It’s a pathogen causing meningitis. You can get pneumonia, but very rare. It’s also betahemolytic so it might be difficult to differentiate just based on that. It’s known as the Group B strep that women are tested for before they give birth.

[13:20] More About Streptococcus Pneumoniae

Streptococcus pneumoniae is the most common type of pneumonia which you will see in the community almost all the time. It’s very much affiliated with the alpha-hemolytic reaction as well as the gram-positive cocci in pairs.

It can be very easily treated with a penicillin G or amoxicillin. If you’re allergic to penicillin, you can do a third-generation cephalosporin. Or if you really need penicillin, you can desensitize someone. But for strep pneumonia, there are other options.