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

Vancomycin

The correct answer is option 2. Vancomycin.

Here is an explanation of each antibiotic's spectrum of activity:

1. Ofloxacin

Broad-spectrum: Ofloxacin is a fluoroquinoloneantibiotic. It works by inhibiting bacterial DNA gyrase and topoisomerase IV, which are essential for DNA replication and repair. This mechanism allows it to be effective against a wide variety of Gram-negative and Gram-positive bacteria, making it broad-spectrum.

Commonly used to treat infections like urinary tract infections, respiratory tract infections, and skin infections.

2. Vancomycin

Narrow-spectrum: Vancomycin is primarily effective against Gram-positive bacteria, particularly Staphylococcus aureus (including MRSA) and Streptococcus species. It works by inhibiting bacterial cell wall synthesis.

Although it is powerful against certain resistant organisms like MRSA, its action is limited to Gram-positive bacteria, which makes it a narrow-spectrum antibiotic.

It does not work against most Gram-negative bacteria.

3. Penicillin

Broad-spectrum: Penicillin is one of the first antibiotics ever discovered and is typically used to treat infections caused by Gram-positive bacteria (like Streptococcus and Staphylococcus). However, amoxicillin and ampicillin (extended-spectrum penicillins) are considered broad-spectrum because they can also be effective against some Gram-negative bacteria.

While classical penicillins mainly target Gram-positive organisms, broader forms of penicillin are effective against a wider variety of bacteria.

4. Chloramphenicol

Broad-spectrum: Chloramphenicol is an antibiotic that inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. It has broad-spectrum activity and can target a wide range of Gram-positive and Gram-negative bacteria.

Chloramphenicol is used to treat infections like meningitis, typhoid fever, and certain types of eye infections. However, due to its potential for serious side effects, it's often reserved for more serious infections when other antibiotics are ineffective or unavailable.

Why Vancomycin is Not Broad-Spectrum:

Vancomycin primarily targets Gram-positive bacteria. It is particularly effective against MRSA (Methicillin-resistant Staphylococcus aureus) and Clostridium difficile infections but is largely ineffective against Gram-negative organisms.

Gram-negative bacteria have a more complex outer membrane, which acts as a barrier to vancomycin and many other antibiotics.

Vancomycin's limited spectrum (mainly targeting Gram-positive bacteria) makes it narrow-spectrum, unlike ofloxacin, penicillin, or chloramphenicol, which can act on a broader range of bacterial species.

Vancomycin is classified as a narrow-spectrum antibiotic, primarily effective against Gram-positive bacteria, particularly resistant strains like MRSA.

Ofloxacin, penicillin, and chloramphenicol are considered broad-spectrum antibiotics, as they target a wider range of both Gram-positive and Gram-negative bacteria.