Which among the following is not a broad-spectrum antibiotics?

Penicillin

The correct answer (3) Penicillin.

Penicillin is a narrow-spectrum antibiotic while the others are broad-spectrum antibiotics:

Penicillin

Penicillin is a beta-lactam antibiotic, which means that it works by inhibiting the synthesis of bacterial cell walls. Cell walls are essential for the survival of bacteria, as they provide them with protection from osmotic pressure and mechanical stress. Penicillin is only effective against bacteria that have cell walls, such as Gram-positive bacteria. Gram-negative bacteria also have cell walls, but they have an additional outer membrane that makes them resistant to penicillin.

Ofloxacin

Ofloxacin is a fluoroquinolone antibiotic, which means that it works by inhibiting the activity of DNA gyrase, an enzyme that is essential for bacterial DNA replication. Fluoroquinolones are broad-spectrum antibiotics because they are effective against a wide range of bacteria, including both Gram-positive and Gram-negative bacteria.

Vancomycin

Vancomycin is a glycopeptide antibiotic, which means that it is a large molecule that consists of a sugar chain linked to a peptide chain. Vancomycin works by inhibiting the synthesis of bacterial cell walls. It is a broad-spectrum antibiotic because it is effective against a wide range of bacteria, including both Gram-positive and Gram-negative bacteria.

Chloramphenicol

Chloramphenicol is a bacteriostatic antibiotic, which means that it stops bacteria from growing. It works by inhibiting protein synthesis in bacteria. Chloramphenicol is a broad-spectrum antibiotic because it is effective against a wide range of bacteria, including both Gram-positive and Gram-negative bacteria.