A superinfection is defined as an infection that comes second to an initial infection and is often caused by the elimination of normal flora by an antibiotic.

Normal flora are the microorganisms that normally live in the human body and help prevent the growth of harmful pathogens.

When an antibiotic kills the normal flora, it creates an opportunity for other microorganisms to overgrow and cause a new infection.

Choice A is wrong because a resistant infection is an infection that does not respond to an antibiotic due to the presence of resistant bacteria.

Resistance can occur when bacteria mutate or acquire genes that make them able to survive the antibiotic.

Choice C is wrong because a nosocomial infection is an infection that is acquired in a hospital or health care setting.

Nosocomial infections can be caused by various factors, such as exposure to contaminated equipment, poor hygiene practices, or transmission from other patients or staff.

Choice D is wrong because an allergic reaction is an immune response to a foreign substance that is not harmful.

Allergic reactions can occur when a person is sensitive to an antibiotic or any other drug.

Symptoms of an allergic reaction may include rash, itching, swelling, or difficulty breathing.