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2518 Microbiology

A 9-year-old child is brought to the emergency room with the chief complaint of enlarged, painful axillary lymph nodes. The resident physician also notes a small, inflamed, dime-sized lesion surrounding what appears to be a small scratch on the forearm. The lymph node is aspirated and some pus is sent to the laboratory for examination. A Wahin-Starry silver impregnation stain reveals many highly pleomorphic, rod-shaped bacteria. The most likely cause of this infection is

AY. pestis
BMycobacterium scrofulaceum
CB. canis
DBaonella henselae
Microbiology
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2520 Microbiology

A superantigen is a bacterial product that –

ABinds to B7 and CD28 costimulatory molecules
BBinds to the beta chain of TCR and MHC class II molecules of APC stimulating T cell activation
CBinds to the CD4+ molecule causing T cell activation
DIs presented by mactrophages to a larger-than-normal number of T helper CD4 + lumphocytes
Microbiology
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