What is a delayed reaction that can occur with PCNs?

The correct choice is superinfections, such as Clostridium difficile colitis, because these reactions can occur as a result of antibiotic treatment, including penicillin (PCN). Delayed reactions typically encompass adverse effects that are not immediate and can arise from alterations in the normal microbiota due to the antibiotic's action. Penicillins can disrupt the balance of gut flora, allowing opportunistic pathogens like C. diff to proliferate, which can lead to gastrointestinal symptoms associated with colitis.

The other options represent different types of reactions. Allergic rhinitis is an immediate hypersensitivity reaction that does not qualify as a delayed response. Anaphylaxis is a severe and rapid allergic reaction, also immediate, which occurs shortly after exposure to the allergen. A rash on the face could be associated with drug hypersensitivity but can occur relatively quickly after administering the drug rather than being classified as a delayed reaction. Therefore, superinfections are the most fitting delayed response associated with penicillin use.