A clinical microbiology laboratory is using flow cytometry to analyze lymphocyte subsets in a patient with suspected immunodeficiency. Which of the following cell surface markers is typically used to identify helper T cells?

A clinical isolate of Klebsiella pneumoniae from a patient with a refractory urinary tract infection exhibits resistance to carbapenems (imipenem, meropenem, ertapenem). PCR analysis reveals the presence of the blaKPC gene. Which of the following enzymatic mechanisms is responsible for this resistance?

A Gram-positive rod is isolated from the blood culture of a neonate with sepsis. The organism exhibits weak beta-hemolysis on sheep blood agar, is catalase-positive, hydrolyzes esculin in the presence of bile, and demonstrates characteristic "tumbling" motility in a wet mount prepared from a broth culture incubated at 25° C. Which organism is most likely? 

During an investigation of a foodborne outbreak linked to a church supper, 80 people ate the suspected chicken dish, and 32 subsequently developed gastroenteritis. Among 50 people who did not eat the chicken dish, 5 developed similar symptoms. What is the attack rate among those who ate the chicken dish? 

A microbiology laboratory is processing a stool sample for ova and parasites. A large (approximately 100 µm), thick-shelled, oval egg with a flattened side is observed. This egg MOST likely belongs to: