Staphyloccocus aureus are Gram positive cocci. Chlamydia trachomatis and Rikettsia prowazekii are both classified as Gram negative rods and Neisseria meningitidis are Gram negative cocci.

All of the bacteria listed are Gram positive except Salmonella, which is a Gram negative facultative rod. 

The Gram stain is a test used to help classify bacteria based on the presence of peptidoglycan in the cell wall. Bacteria with a thick peptidoglycan cell wall will stain dark purple, and are termed Gram positive. On the other hand, if there is no peptidoglycan cell wall (or a very thin one), it will show up as pink. This is termed Gram negative. This distinction is particularly important when prescribing classes of antibiotics, as the cell wall is commonly targeted by antibiotics. 

A nosocomial infection is an infection that is transmitted from one person to another inside the hospital or other healthcare facility. It is often a result of healthcare workers failing to preform adequate hand hygiene and standard precautions. Those most at risk for infection are those who are immunocompromised (chemotherapy patients), those with breaks in skin integrity (wounds), and those with invasive devices (PICC lines, urinary catheters, invasive monitoring). 

A pathogenic bacteria is a disease-causing bacteria. They may secrete toxins to make a host ill or reproduce inside the host's own cells. Bacteria may have cell walls, although some do not. Similarly, some bacteria may have flagella and others do not. It is typical for viruses to have a capsid (protein coat). Some viruses such as the human immunodefficiency virus (HIV) have envelopes, which makes it difficult for the immune system to detect and destroy them.  

C. difficile is an endospore-forming bacteria. While in the endospore (or dormant) stage, C. difficile spores are highly resistant to disinfectants. This renders sterilization procedures less effective in a hospital setting and leads to a higher frequency of infection. While route of transmission and hospital sanitation are important factors in C. difficile transmission, it is their endospore formation that gives these bacteria a level of resistance above other fecal-oral species present in a hospital setting.

Antibiotics work exclusively against bacteria. They are not effective against fungal infections, and they are not effective against viruses such as influenza, rotovirus, or rhinovirus (the most frequent cause of the common cold). 

Pili are short, hairlike structures on the surface of some bacteria. Conjugative pili can form a sort of tube between bacterial cells, allowing for the transfer of DNA from one bacteria to another.

Flagella are whip-like structures that allows bacteria to move within a fluid medium. Cilia are hair-like structures found primarily on the surface of mammalian cells, but are also found on bacterial cells, where they aid in attachment. A bacterial capsule is a polysaccharide layer outside the cell envelope that does not take part in bacterial conjugation, and may secrete "slime" which protects the bacteria from the surrounding environment.

The process of asexual reproduction in which a single-celled organism divides into two cells of the same size is called binary fission. This occurs among prokaryotes and is the primary method of reproduction in bacterial species. Mitosis and meiosis are forms of cell division among eukaryotic cells. Conjugation is not a method of bacterial reproduction; rather, it is a method by which joined bacteria may transmit DNA, especially genes on plasmids that confer resistance. 

Gram negative strains of bacteria possess more lipopolysaccharide than do Gram positive strains. This higher proportion of lipopolysaccharide lies on the exterior of Gram negative bacteria's outer membranes of their cell walls. Gram negative bacteria have significantly less peptidoglycan than do Gram positive strains, which accounts for their observable chromatic differences when using the Gram stain technique. Specifically, the this thin layer of peptidoglycan in Gram negative bacteria fails to retain crystal violet during Gram staining, especially after iodine is added, which acts as a mordant. Subsequent staining with safranin gives Gram negative bacteria a pink or light red color when viewed under a light microscope. Teichoic acid, present in Gram positive bacteria only, functions to increase the rigidity of the cell wall. Murein is another name for peptidoglycan.