A 10-year-old boy is brought to the clinic by his mother. She noted that his face is swollen, and he told her that his urine was cloudy and reddish. He has a history of falling and abrading the skin of his right thigh 2 weeks ago. The next day, the skin became red, hot, and tender; the infection was treated with a topical antibiotic ointment. The cellulitis gradually healed.

What organism is the most likely cause of this patient's disease?
a. Staphylococcus aureus
b. Streptococcus pyogenes
c. Escherichia coli
d. Pseudomonas aeruginosa