Final answer:
Bacteria defend against phage infection using restriction endonucleases and an adaptive immune system like the CRISPR-Cas system. Bacteriophages can also be used in phage therapy, offering a potential solution to antibiotic-resistant bacterial infections, like MRSA, by targeting and killing specific bacteria without affecting beneficial microbiota.
Step-by-step explanation:
Bacteria have evolved various defense mechanisms to protect against phage infection. One such defense is the use of restriction endonucleases, which recognize and digest foreign phage DNA, thereby protecting the bacteria from infection. Additionally, bacteria utilize an adaptive immune system known as the CRISPR-Cas system, where they integrate segments of phage DNA as spacers into their genomes to 'remember' past infections. If the same phage attempts to infect the bacteria again, the CRISPR system can rapidly destroy the incoming phage DNA to prevent the infection.
In the realm of medicine, bacteriophages have been harnessed for phage therapy, particularly as an alternative to antibiotics in the treatment of antibiotic-resistant bacteria like MRSA. This is done by using specific bacteriophages that infect and kill the bacteria without harming the beneficial normal microbiota of the body. The U.S. Food and Drug Administration has approved the use of bacteriophages to spray meats in an effort to eliminate foodborne pathogens like Listeria, confirming the safety of bacteriophages under certain conditions.