QuestionSBA
QuestionChoice
Previously known as *Pneumocystis carinii*, this yeast-like fungus is an opportunistic agent and a common cause of pneumonia in patients who have HIV.
10003498
c
*Pneumocystis jirovecii*
QuestionChoice
This is a Gram-negative rod-shaped bacterium associated with pneumonia. It typically causes pneumonia in patients at high risk of aspiration. Alcoholism is also a well-known risk factor.
10003499
d
*Klebsiella pneumoniae*
QuestionChoice
This is a gram-negative cocci that can cause ear, upper respiratory tract, and lower respiratory tract infections. It is also known as *Branhamella catarrhalis*.
10003497
b
*Moraxella catarrhalis*
QuestionChoice
This patient has developed a community–acquired pneumonia (CAP). Other potential differentials include pulmonary embolism, acute bronchitis and acute exacerbation of COPD. However, this patient's symptoms - particularly the fever, sputum, low oxygen saturations, cough and now a cavitating lesion - point towards a diagnosis of CAP with cavitation.

Furthermore, *Staphylococcus aureus* and *Streptococcus pneumoniae* are the only answer choices that are gram-positive cocci. However, of the two, *Staphylococcus aureus* is arranged in grape-like clusters or 'clumps', whereas Streptococci are arranged in chains or pairs (diplococci).
10003496
a
*Staphylococcus aureus*
QuestionChoice
This is a Gram-positive spherical bacteria, usually found in pairs (diplococci). *Streptococcus pneumoniae* is the most common cause of community-acquired pneumonia.
10003500
e
*Streptococcus pneumoniae*
Concept
Chapter
2693
3709
Pneumonia
Topic
132
Respiratory
13246
A 39-year-old woman presents to A&E with a one-week history of dyspnoea and cough, bringing up increasing amounts of sputum.

She has a fever, a respiratory rate of 26 breaths per minute and is saturating 92% on room air.

A chest x-ray shows a cavitating lesion in the right middle zone. Microscopy shows Gram-positive cocci.

She has not been in contact with any unwell persons nor does she have a history of tuberculosis. She is a known IV drug user.

What is the most likely causative organism of this woman's symptoms?
a