Final answer:
Bacteria can be resistant to antimicrobials due to the activity of efflux pumps, which actively transport antimicrobials out of the cell, preventing drug accumulation and contributing to multidrug resistance.
Step-by-step explanation:
Some bacteria are resistant to antimicrobials due to the activity of efflux pumps, which remove many of them. Efflux pumps are intrinsic membrane proteins that actively transport an antimicrobial drug out of the cell, thereby preventing the accumulation of the drug to a level that would be antibacterial.
This resistance mechanism is commonly effective against a wide range of antimicrobials in multiple classes, including B-lactams, tetracyclines, and fluoroquinolones. It is quite common for a single efflux pump to have the ability to translocate multiple types of antimicrobials, a phenomenon known as multidrug resistance.