Final answer:
The statement that only phages are capable of immunity is false; both bacteria and multicellular organisms have immune systems. Phage therapy, which uses phages to target specific bacteria, is a promising alternative to antibiotics. The lytic and lysogenic cycles are key to understanding how bacteriophages interact with host cells.
Step-by-step explanation:
The statement that only phages are capable of immunity is false. Phages, or bacteriophages, are viruses that infect bacteria, not immune entities themselves. However, bacteria possess a form of adaptive immunity known as CRISPR-Cas, which allows them to 'remember' past phage infections and defend against them. In addition, all multicellular organisms, including humans, have complex immune systems that include a variety of cells capable of phagocytosis, which is the process of engulfing and digesting pathogens and other particles.
Scientists have indeed identified viruses that can infect fungal cells, proving that the range of viruses extends beyond just phages. It is also true that there are different types of immune system cells, such as macrophages and neutrophils, capable of carrying out phagocytosis. And substances like semen can function as chemical barriers that protect against pathogens by creating environments hostile to them.
Phage therapy takes advantage of the specificity of phages: a phage infects and kills only a particular type of bacterium, leaving the body's beneficial microbiota intact, unlike broad-spectrum antibiotics. This therapy has been used in parts of Eastern Europe and the former Soviet Union as an alternative to antibiotics, especially useful against multi-drug-resistant bacterial strains. However, it's important to note that phages can sometimes increase bacterial virulence, such as in the case of MRSA.
The lytic and lysogenic cycles are two pathways that bacteriophages can follow when infecting bacterial cells. In the lytic cycle, phages are produced and released into the environment following the lysis of the host cell. On the other hand, the lysogenic cycle involves the incorporation of phage DNA into the host genome without immediate lysis.
Additionally, bacteria using the CRISPR system may acquire spacer DNAs that provide a record of past viral infections, thus conferring a form of memory to the bacterial immune defense.