Which of the following is a narrow-spectrum antibiotic?

Streptomycin is considered a narrow-spectrum antibiotic primarily effective against specific types of bacteria, particularly gram-negative organisms and some mycobacteria. This targeted action means it is used for treating infections caused by these particular pathogens, making its use more specialized compared to broad-spectrum antibiotics, which target a wider range of bacteria.

Narrow-spectrum antibiotics like streptomycin are advantageous because they minimize disruption to the normal flora of the body and reduce the risk of developing antibiotic resistance. This characteristic is critical in the management of infections caused by well-defined pathogens, such as those seen in tuberculosis or certain bacterial infections.

In the context of the other options, tobramycin, ciprofloxacin, and levofloxacin are broader-spectrum antibiotics. They cover a wider range of bacteria, including both gram-positive and gram-negative organisms, which is why they are utilized for a variety of infections, making them distinctly different from the narrow-spectrum action of streptomycin.