ABC transporters utilize the energy of ATP hydrolysis to transport various substrates across cellular membranes. In prokaryotes, importers mediate the uptake of nutrients into the cell. The substrates that can be transported include ions, amino acids, peptides, sugars, and other molecules that are mostly hydrophilic. The membrane-spanning region of the ABC transporter protects hydrophilic substrates from the lipids of the membrane bilayer thus providing a pathway across the cell membrane. Transporters are extremely vital in cell survival such that they function as protein systems that counteract any undesirable change occurring in the cell. For instance, a potential lethal increase in osmotic strength is counterbalanced by activation of osmosensing ABC transporters that mediate uptake of solutes. Other than functioning in transport, some bacterial ABC proteins are also involved in the regulation of several physiological processes. ABC transporters are known to play a crucial role in the development of multidrug resistance.