Microbiology-Typical CAP Flashcards
How does hospital-acquired pneumonia typically differ from community acquired pneumonia?
In hospital acquired pneumonia is usually caused by enteric gram-negative rods (Klebsiella pneumoniae and e. coli)
Your neighbor decides to not get a flu shot and comes down with the flu. A week later he is still sick, complaining of fever, chills and chest pain. When you take him to the ED, CXR reveals right lower lob consolidation. What is the most likely pathogen causing this patient’s symptoms? What other condition is often caused by this pathogen?
Strep pneumoniae is the most common cause of secondary bacterial pneumonia after influenza infection. This is due to epithelial damage by the influenza virus that makes a nice seeding ground for strep pneumoniae. It also often results in otitis media.
A patient comes to the ED with fever, chills and pleuritic chest pain. Blood test reveal elevated CBC and a gram-positive, catalase-positive and coagulase positive rod. CXR shows left middle lobe consolidation. What pathogen is causing pneumonia in this patient?
Community acquired staph aureus.
A patient comes to the ED with fever, chills and pleuritic chest pain. Blood test reveal elevated CBC and a small gram-negative rod that only grows on chocolate agar. He has a history of COPD. CXR shows left middle lobe consolidation. What pathogen is causing pneumonia in this patient?
Community acquired H. influenzae. It needs X and V to grow and thus will only grow on chocolate agar.
A 47 year old female presents to your clinic with dry cough, headache and fatigue. Her WBC is elevated with a left shift and CXR shows a diffuse pattern. What are likely pathogens causing her condition?
This is atypical community acquired pneumonia or “walking pneumonia”. This is often caused by mycoplasma pneumoniae, chlamydia pneumoniae and legionella pneumophila.
What pathogens cause sub acute pneumonias?
Tb or fungal infections.
What determines if strep pneumoniae can cause disease or not?
Only the encapsulated form (glistening as seen below) can cause disease.
Your neighbor decides to not get a flu shot and comes down with the flu. A week later he is still sick, complaining of fever, chills and chest pain. When you take him to the ED, CXR reveals right lower lob consolidation. His blood culture is shown below and is catalase-negative. What is the most likely pathogen causing this patient’s symptoms?
Note the alpha-hemolytic (green color) diplococci. This combined with the fact that strep pneumoniae is the most common cause of secondary bacterial pneumonia after influenza makes it the most likely pathogen.
How does the laboratory differentiate between the alpha-hemolytic strep viridans that causes endocarditis and the alpha-hemolytic strep pneumoniae that causes pneumonia?
Strep pneumoniae is sensitive to optochin (bile salt that triggers autolytic enzymes) and viridans is not.
Why do encapsulated organisms have a higher survival rate in the blood stream and are thus more virulent?
It allows them to avoid complement by interfering with C3b deposition. Absence of C3b recognition = no recognition by PMNs.
Why are antibodies a successful mode of elimination of encapsulated bacteria?
Each capsule is unique. The Fab portion of the antibody binds to the capsule and the Fc region binds to the phagocyte, triggering phagocytosis of the encapsulated bacteria.
Why is strep pneumoniae less likely to cause pneumonia in someone who does not have influenza?
There is no epithelial damage that makes a good seeding ground for strep pneumoniae and you body gets rid of it quickly.
What are the predisposing factors to getting pneumococcal pneumonia?
Viral infection, Compromised pulmonary function (alcoholism, general anesthesia), Age (elderly and <2), ethnicity/race. Impaired immunity and finally a more virulent serotype of strep pneumoniae.
A 72 year old female comes to your clinic with a sudden onset of chills, fever, pleuritic pain and rusty-colored sputum. He has a history of alcoholism and his chest x-ray is shown below. Where is the oldest lesion seen in this patient’s lung and what would you suspect to find on a blood culture?
The oldest lesion would be in the center of the consolidated left lobe. On blood culture you would expect to find a gram-positive, catalase-negative, alpha-hemolytic, optochin sensitive, bile soluble diplocci, i.e. strep pneumoniae.
Death occurs in 14% of patients who get pneumococcal pneumonia. What is the usual cause of their death?
Pneumonia, bacteremia, meningitis and otitis media.
What is PCV13?
Pneumococcal conjugate vaccine that is specific for 13 different serotypes of strep pneumoniae. This is an expensive vaccine because it is a conjugate (protein/carbohydrate T-dependent antigen) which is necessary for young children because their immune systems don’t do a great job at recognizing polysaccharides (T-independent antigens).
