Answer: Their quick growth and reproduction rates, which also leads to antibiotic resistance
Explanation:
Bacteria are single-celled prokaryotic organisms (whose genetic material is not condensed inside a membranous nucleus) that reproduce mostly via asexual reproduction, where one cell originates a new one via mitosis. Bacteria can establish colonies very rapidly once the conditions for their reproduction are guaranteed. When bacteria infect a host, the infected surface has the nutrients that the colonies require to reproduce. Because they have very quick reproduction rates, their evolvability, the capacity to change and adapt to new conditios, is also higher.
The most effective way to deal with bacterial infections is with antibiotics, molecules that interfere with the cell metabolism of the bacteria. This is possible to administrate to animals and plants because they are eukaryotes, a different type of cell.
Antibiotics mostly target growth processes, because reaching an optimal growth is a requisite to ensure mitosis. Most antibiotics target the bacterial cell wall, such as penicillins and cephalosporins, but others such as polymixins target the cell membrane. The structure of the cell wall and cell membrane is essential for the bacteria to let the nutrients in. Other antibiotics target essential enzymes that let the bacteria perform their metabolism, such as rifamycins that block the synthesis of proteins, lipiarmycins that block the transcription of RNA, or quinolones that block DNA replication. These antibiotics are called bactericidal, because their main goal is to kill the bacteria withouth lethally harming the host.
Although some antibiotics are synthetic, most of them are naturally produced by other bacteria or fungi as a defense mechanism. This allows one colony of bacteria of one species to reduce the population of another competing species. Antibiotics in the natural world are a consequence of antagonistic relationships between species.
Because of their high rates of evolvability and antibiotics being produced by bacteria, some bacteria can acquire resistance towards antibiotics if only a few cells survive the antibiotics course. Moreover, bacteria can transfer this resistance to other cells of the same species, spreading genes that confer resistance more quickly.
