A 40-year-old man has been bothered by oral candidiasis, fever, and diarrhea for the past year. On physical examination, he has muscle wasting. His weight is 70% of normal for his height and age. He has generalized nontender lymphadenopathy, but no hepatosplenomegaly. He developed three irregular, 1- to 2-cm, reddish-purple, nodular skin lesions on his forearm in the past 3 months. Laboratory findings show hemoglobin, 12.2 g/dL; hematocrit, 36.5%; MCV, 85 mm3; platelet count, 188,000/ mm3; and WBC count, 2460/ mm3 with 82% segmented neutrophils, 4% bands, 6% lymphocytes, 6% monocytes, and 2% eosinophils. Infection with which of the following organisms is most likely to produce these findings?