Bacteria are capable of reproducing in a variety of ways. Binary fission is most similar to mitosis in animals, and does not involve any genetic recombination. DNA is replicated and passed to identical daughter cells.

In contrast, the other listed methods involve the incorporation of foreign DNA into the bacteria genome. In conjugation, plasmids are exchanged between bacteria via a sex pilus. In transformation the bacterium is capable of incorporating DNA directly from its surrounding environment. In transduction, a bacteriophage vector is used to introduce foreign DNA into the bacterial cell.

Peptidoglycan is most well-known for its role in the formation of bacterial cell walls. By inhibiting the production of peptidoglycan, penicillin prevents bacteria from fully developing and is very effective at treating bacterial infections.

Anti-histamines an anti-inflammatory medications can be used to help prevent the autoimmune response that triggers allergic reactions. Fungicides are used to kill fungal infections. Viruses are harder to treat, as they are not technically alive and cannot be "killed."

Bacteria are single-celled organisms that reproduce by binary fission, in which identical copies of the original cell are produced.

Viruses require living cells in order to multiply. The viruses invade cells and redirect the host organelles from their normal functions to instead replicate the virus. Fungi are very different from bactria in that their structure is more complex (eukaryotic) and they reproduce by budding (among other mechanisms). Protozoa include unicellular animal-like microorganisms. Common protozoan infections include malaria and sleeping sickness. Helminths are worm-like animals, including pinworms and tapeworms. 

Endospores are produced by gram-positive bacteria and can lie dormant for years. Endospores are crucial to growth of gram-positive bacteria because they resist harsh conditions such as extreme temperatures, ultraviolet radiation, and many chemicals. Endospores are not used by fungi by any means. They are also uninvolved in the reproductive processes of bacteria. 

The main reaction that happens during a gram stain is the detection of the presence of peptidoglycan. Most bacterial cell walls contain peptidoglycan, but in varying amounts. If the cell contains large amounts of peptidoglycan, it will retain the crystal violet dye and display a purple coloration (this is gram-positive). If the cell does not contain a large quantity of peptidoglycan, it will display the counterstain and appear pink (this is gram-negative).

The gram-stain does not dictate whether or not a species belongs to the domain archaea. Archaea cell walls do not contain peptidoglycan and will not react to the stain. Note that archaea and bacteria are different domains altogether, though they share some similar characteristics.

There are three principal forms of bacteria. Spherical bacteria are termed cocci. Rod-shaped bacteria are called bacilli. Spiral bacteria are rigid (spirilla), flexible (spirochetes), or curved (vibrios). 

Streptococcus, the causative agent of strep throat, is a genus of gram-postitive (purple staining) cocci (spheres), in which the cells tend to form chains. Bacteria are described by a combination of their response to gram stain and their appearance. For example, "gram-positive streptococcus" indicate chains of spheres that stain purple. 

The peptidoglycan layer of bacteria retains the Gram stain. In general, Gram-negative bacteria are more virulent than Gram-positive bacteria. This is due in part to an outer layer of lipopolysaccharides present on Gram-negative bacteria that invokes immune responses (particularly via a component called lipid-A), and are somewhat more difficult to target with antibiotics.