- NAD (Nicotinamide adenine dinadeotide)
- A coenzyme necessary to transfer hydrogen atoms.
- Naturally acquired active immunity
- A type of immunity produced when an organism is exposed to an infectious agent.
- Naturally acquired passive immunity
- A type of immunity produced when antibodies, made by a pregnant woman’s immune system, are transferred across the placenta to her fetus or in the colostrum of her breast milk.
- Necrosis
- The death of a defined area of tissue.
- Negri bodies
- Oval or round bodies in the nerve cells of dead rabid animals, seen within the hippocampus of the brain of individuals who have died of rabies.
- Neisseria
- A species of bacteria from the family Neisseriaceae producing diseases commonly referred to as meningococcus and gonorrhea.
- Nematodes
- Unsegmented threadlike worms of the class Nematoda, phylum Aschelminthes; in some classifications, they are sometimes known as Nemathelminthes or a class of that phylum. There are about 12,000 classified species, but an estimated 200,000 plus are known to exist. Nematodes commonly include such worms as the roundworm, pin worm, and hookworm, but not tapeworms (Cestodes) or flukes (Trematodes). They are multicellular organisms and larger than Protozoa.
- Nervous system
- Consists of the brain, optic nerves, and spinal cord.
- Neurocysticerocosis
- An infection of the brain, spinal cord, or eye caused by the larval form of the pork tapeworm Taenia solium.
- Neutrophile
- A granulocyte that is heavily involved in the inflammatory response and a major component of pus.
- Neurotoxin
- A toxin that acts on nervous system tissues.
- Night soil
- The name given to human excretement used as fertilizer.
- Nitrifying
- A type of bacteria responsible for the oxidation of ammonia.
- NK (natural killer)
- A type of T cell operating, within the first day or two of an infection, as part of the early defence system. Unlike other T cells, the NK cell does not recognize individual antigens, but kills cells that are not displaying MHC class 1 labels. These are ones usually infected with viruses.
- Nongonococcal urethritis
- A gonorrhea-like sexually transmitted disease most often caused by Chlamydia trachomatis and mycoplasmas.
- Nosocomial
- An infection acquired in a hospital.
- Nonspecific
- A type of defence against pathogens operating regardless of the invading agent.
- Nonspore-forming, nonfermentative, Gram-negative bacilli
- A large number of genera of bacteria that usually produce disease only in the immune compromised. Their natural habitat is the environment, but they are able to produce disease in humans. They can be motile or nonmotile, but the most distinguishing characteristic is that they are nonfermentive, which means they lack the anaerobic breakdown of carbohydrates. They do utilize carbohydrates, but do so without producing the acid or alcohol end products necessary for fermentation. Another common feature in this group is that they produce similar infections, but are not known for a particular disease. They are also responsible for about 15% of the nosocomial infections, as urinary tract infections stemming from the use of indwelling catheters, infections acquired in burn units, bacteremia and pneumonia. This group is often resistant to many antimicrobials, so therapy is difficult. The most frequently involved genera in the clinical setting includethe following: Pseudomonas, Acinetobacter, Alcaligenes, Moraxella, and Eikinella. Often referred to as “water bugs,” this group of bacteria is fond of standing moisture, and pose a particular threat through the use of various breathing apparatuses where water droplets can stagnate if proper cleaning is not done. Other potential water contamination units include vessels used to heat babies’ bottles, vases that hold flowers, sumps for humidifiers, whirlpools, and drinking fountains or dispensers.
- Non-spore forming bacterial diseases
- Include: Bacteroides (Gram-positive bacilli), particularly B. fragilis, are responsible for over 90% of the infections involving abdominal abscesses. These often occur after fecal material enters the abdominal cavity as a result of injury, surgery, appendicitis, or cancer. These bacteria are also responsible for abscesses of the female reproductive organs following abortions, surgery, cancer, extensive medical manipulations, prolonged labor, intrauterine contraceptive devices, and gonorrhea. PID (pelvic inflammatory disease) is also associated with these bacteria. More than half of all liver abscesses are caused by these anaerobic bacteria, and 90% of all respiratory tract infections have cultures positive for non-spore-forming anaerobes. Infections may also develop in the skin, muscle, and connective tissue following injury, surgery, or lack of blood supply, and from human bites. Septicemia can result from an invasion of the bloodstream by non-spore-forming bacteria, which happens in about 10% of the cases. Brain abscesses can also be caused by bacteroides and anaerobic cocci. Treatment of these conditions is often difficult, but usually involves drainage or surgical removal of dead tissue. Antibiotic treatment is also difficult since many of these organisms are resistant to penicillins and most cephalosporins.
- Nucleoid
- The aggregated mass of DNA that makes up the chromosome of prokaryotic cells.
