This tissue gram stain of an acute pneumonia demonstrates dark purple dot-like gram positive cocci that have been eaten by the numerous PMN's exuded into the alveolar space. Opsonins such as IgG and C3b facilitate the attachment of PMN's to offending agents such as bacteria so that the PMN's can phagocytose them. An elevated serum procalcitonin level is a marker of severe sepsis.

Question: What organisms may be implicated?

AnswerCommon gram positive cocci causing pneumonia include streptococci (Streptococcus pneumoniae, Enterococcus) and Staphylococcus aureus.



Zinc is a key micronutrient for both microbial pathogens and human host cells, particularly immune cells. Zinc can be concentrated by phagocytic cells, particularly neutrophils containing a cytoplasmic protein call calprotectin. These phagocytes can then signal T lymphocytes for an adaptive immune response, and they can concentrate free zinc toxic to microbes. Measurement of calprotectin can provide a means for assessing the magnitude of an inflammatory reaction, such as stool calprotectin measurement to gauge inflammatory bowel disease.