A drug that is a fifth-generation cephalosporin which is the first in its class effective against MRSA is:

A. Macrophage: This is the correct answer. An activated monocyte is also known as a macrophage. Monocytes are white blood cells that can mature into macrophages when they move into tissues. Macrophages play a crucial role in the immune system by phagocytosing (engulfing and digesting) pathogens and cellular debris.

B. Lymphocyte: Lymphocytes are another type of white blood cell that plays a central role in the immune system. They include B cells, T cells, and natural killer cells. Lymphocytes are primarily involved in adaptive immune responses, such as antibody production (B cells) and cell-mediated immune responses (T cells).

C. Plasma Cell: Plasma cells are a type of B cell that produces antibodies (immunoglobulins). They are involved in the adaptive immune response, specifically in the production of antibodies that target specific pathogens.

D. Polymorphonuclear Leukocyte: This term typically refers to a group of white blood cells that have a multi-lobed nucleus. Neutrophils, eosinophils, and basophils are examples of polymorphonuclear leukocytes. They are involved in innate immune responses, including the phagocytosis of pathogens.

A. "Bactericidal and bacteriostatic are used interchangeably."
Explanation: This statement is incorrect. Bactericidal and bacteriostatic are two distinct categories of antibiotics with different mechanisms of action.

B. "Bactericidal drugs are directly lethal to bacteria, and bacteriostatic drugs work to slow bacterial growth but do not cause cell death."
Explanation: This statement is correct. Bactericidal drugs kill bacteria directly, leading to their death, while bacteriostatic drugs inhibit bacterial growth without causing immediate cell death.

C. "Bacteriostatic drugs are directly lethal to bacteria, and bactericidal drugs work to slow bacterial growth but do not cause cell death."
Explanation: This statement is incorrect. It is the opposite of the correct explanation. Bacteriostatic drugs do not directly kill bacteria, and bactericidal drugs do cause bacterial death.

D. "A bactericidal drug can cause death to the host, whereas a bacteriostatic drug only affects bacteria."
Explanation: This statement is not entirely accurate. While some bactericidal drugs can be more toxic to the host, it depends on the specific drug and its dosage. Bacteriostatic drugs, on the other hand, generally do not directly harm the host. The primary distinction between the two categories is their impact on bacterial growth and survival.