Which microorganism is responsible for causing antibiotic-resistant infections?

The correct choice is bacteria because they are the primary microorganisms known to develop antibiotic resistance. This process occurs through various mechanisms, such as mutations or the horizontal transfer of resistance genes between bacteria, often exacerbated by the overuse or misuse of antibiotics. As a result, infections caused by antibiotic-resistant bacteria can become difficult to treat, leading to longer hospital stays, higher medical costs, and an increased risk of mortality.

While fungi, protozoa, and viruses can also cause infections, they typically do not exhibit antibiotic resistance in the same context as bacteria. Fungal infections may resist antifungal agents, and certain protozoa are resistant to specific treatments, but the term "antibiotic resistance" is conventionally associated with bacterial infections. Viruses, on the other hand, are not susceptible to antibiotics at all, as they possess a different structure and life cycle that is not affected by these medications. Thus, when discussing antibiotic-resistant infections, bacteria are the microorganisms of primary concern.