Case 65. MRSA pneumonia (78 y-o M)
    Cavity-forming pneumonia (lung abscess) seen after surgical replacement for aortic dissection    
Key words : 
MRSA, Staphylococcus aureus, lung absces, hospital-acquired infection    
opportunistic infection
Transbronchial infection of MRSA often provokes cavitation in the lung (gross findings).   Coccal colonies are densely surrounded by neutrophils (HE). Strong basophilia of the bacteria in H&E preparation indicates Gram positivity.
The coccal colonies are uniformly Gram-positive (Gram). Microbial culture of the lung tissue obtained at autopsy confirmed nosocomial infection of MRSA.   Reference case 65A
Another autopsy case of hospital-acquired MRSA pneumonia in a post-operative patient of esophageal cancer (68 y-o M). Marked proliferation of cocci are seen in the alveolar space (HE). In this case, microbial culture was not performed at autopsy.
Reference case 65A
MRSA identification by a monoclonal antibody to penicillin-binding protein-2' (PBP2') (immunostaining after heating pretreatment). The detection of immunoreactive PBP2' strongly indicates MRSA infection.
  Reference case 65B
Incidental terminal aspiration of MRSA colonies into the lung, leading to a culture-positive result (HE). Morphologic study can easily distinguish MRSA-induced infection from the carrier state of MRSA without provoking clinical manifestation.