Which antibiotic was used for the first successful treatment of a patient with sepsis in 1942?

The correct answer is penicillin, which marked a significant milestone in medical history as the first antibiotic successfully used to treat sepsis in a patient in 1942. Penicillin, discovered by Alexander Fleming in 1928 and later mass-produced during World War II, changed the landscape of medicine by providing an effective means to combat bacterial infections. Its introduction allowed for the effective treatment of various bacterial diseases, including life-threatening conditions like sepsis, which is the body's extreme response to an infection that can lead to tissue damage and organ failure.

The other options listed, while important antibiotics in their own right, were either developed later or not primarily recognized for their role in the treatment of sepsis during that time period. Cephalexin, a type of cephalosporin antibiotic, was developed in the 1960s. Tetracycline also came into use after penicillin and was introduced in the late 1940s. Erythromycin, discovered in the early 1950s, became another important antibiotic but came later than penicillin and was not the first to demonstrate efficacy against sepsis. Thus, penicillin stands out as the breakthrough treatment that transformed medical approaches to microbial infections in the early 20th century.