Find the Gold Standard!

A 35-year-old diabetic woman presents to her gynecologist with complaints of burning on urination for the past 2 days. Dipstick test of her urine demonstrates markedly positivity for leukocyte esterase, but no reactivity for nitrite. Urine culture later grows out large numbers of organisms. Which of the following bacteria are most likely to be responsible for this patient's infection?

A. Enterobacter sp.
B. Enterococcus faecalis
C. Escherichia coli
D. Klebsiella pneumoniae
E. Pesudomonas aeruginosa



The gold standard in this question is not the culture, because all five of these bugs will grow on agar. Here the gold standard is the "no reactivity for nitrite." Production of nitrites is typically found in gram negatives when the converted nitrate to nitrite (via reductase). So this question boils down to which one of the bugs is the gram positive? Enterococcus (B) is the answer to the question, but I wanted to bring the trickiness of the name Enterococcus to everyones attention. It sounds too similar to the gram negatives sp. Enterobacter. I have confused these two since I opened my first micro book. Nowadays, I consciously slow down my reading whenever I see the word "entero." Enterotoxin and endotoxin are often confused as well. So be careful!