N-acetylmuramic acid : An acetylated amino sugar bearing a lactyl group. Together with N-acetylglucosamine, it forms the polysaccharide backbone of murein, the rigid, cross-linked polymer that forms the rigid portion of a eubacterial cell wall.

NaCl : Sodium chloride.

Nagler test : A test once widely used to presumptively identify Clostridium perfringens. It is used less often in today's laboratories because it is not specific for C. perfringens. The Nagler test employs an antitoxin that will neutralize the lecithinase produced by C. perfringens (and three additional Clostridium spp.)

NaHCO3 : Sodium bicarbonate.

Na2HPO4 : Sodium phosphate.

NaOH : Sodium hydroxide.

Nanophyetus salmincola : A digenetic trematode (acquired by ingestion of raw, undercooked, or smoked salmon), human infections have now been reported from North America. Symptoms include gastrointestinal complaints or unexplained eosinophilia. Eggs were also recovered from the stool specimens.

Nares : External openings of nose (i.e., nostrils).

Nasopharyngeal : Pertaining to the part of the pharynx above the level of the soft plate.

Natural killer (NK) cell : A specialized lymphocyte that recognizes and destroys foreign cells or infected host cells in a nonspecific manner.

NB : Northern Blot (RNA hybridization).

Necropsy : See Autopsy.

Necrosis : Pathological death of a cell or group of cells.

Necrotizing fascitis : A very serious, painful infection involving the fascia (membranous covering) of one or more muscles; may spread widely in short periods of time since there is no anatomic barrier to spread in this type of infection.

Negri bodies : Characteristic virally-induced inclusions present in rabies-infected brain cells.

Neonatal : First 4 weeks after birth.

NEPH : Nephelometry.

Nephelometry (NEPH) , is used to quantitate antigen by analyzing increases in turbidity, as measured by increasing scatter of laser light. The interaction of specific antibodies in the reagent with the antigen from the sample results in the formation of antigen-antibody complexes which are rendered insoluble by the presence of precipitating reagents. Most modern nephelometers compare the rate of formation of antigen-antibody complexes (determined by computer analysis of laser light scatter data) to that of known antigentic standards in order to measure precisely the protein antigens (some of which are actually immunoglobulins) present in moderate concentrations.

Nephrosis : Degeneration of renal tubular epithelium.

Neuropathy : Diseases or disorders affecting the cranial nerves or the peripheral or autonomic nervous systems.

Neuritis : Inflammation of a nerve; most often not caused by and infectious agent.

Neurotrophic : Having a selective affinity for nerve tissue. Rabies is caused by a neurotrophic virus.

Neutralization (NT) , is similar to complement fixation but is applicable only in certain pathogenic situations where the antibody being measured is directed against a hemolysin (a bacterial toxin capable of directly lysing erythrocytes). In these situations, the hemosylin and reagent erythrocytes are added, and if the antibody to the hemosylin is present, the lysis of RBC's will not occur. As in Complement Fixation (CF), crude quantitation is afforded by serial dilution which may be quantitatively compared to established standard material dilutions.

Neutropenia : Abnormally low numbers of neutrophils in the circulating blood.

Neutrophilic : Growing best at pH values near 7.

NFB : Glucose nonfermenting gram-negative bacteria.

NGU : Nongonococcal urethritis.

Nick translation : Use of enzymes to break DNA and repolymerize small sections of the molecule, usually for purposes of labeling the DNA with a radioactive nucleotide.

Nicotinamide adenine dinucleotide (NAD) : An important coenzyme, functioning as a hydrogen carrier in a wide range of redox reactions; the H is carried on the nicotinamide residue. The oxidized form of the coenzyme is written NAD+, the reduced form as NADH (or NADH+H+).

Nicotinamide adenine dinucleotide phosphate (NADP) : An important coenzyme, functioning as a hydrogen carrier in a wide range of redox reactions; the H is carried on the nicotinamide residue. The oxidized form of the coenzyme is written NADP+, the reduced form as NADPH. Many oxidoreductases are specific for either NAD or NADP, although some can function with either. As a broad generalization, NADP is more commonly associated with biosynthetic reactions, NAD with catabolic and energy-yielding reactions.

Nicotinic acid (niacin) : A white crystalline acid that is a component of the vitamin B complex.

NIH : National Institute of Health.

NIOSH : National Institute for Occupational Safety and Health.

Nitrate : Any salt of nitric acid, having the molecular formula NO3-.

Nitrate test : Any test that detects an organism's ability to reduce nitrate to nitrite.

Nitrification : The conversion of ammonia (NH3) to nitrate (NO3-).

Nitrifying bacteria : Chemolithotrophs capable of carrying out the transformations from NH3 to NO2- or NO2- to NO3-.

Nitrogenase : The enzyme complex catalyzing the reaction of nitrogen fixation.

Nitrogen fixation : Reduction of dinitrogen gas (N2) to ammonia (NH3) by the enzyme nitrogenase.

NMR : Nuclear magnetic resonance.

Nocturnal : Pertaining to the dark portion of a 24h day; active at night (filariasis).

Nodular Body : One or more closely intertwined hyphae forming a rounded ball-like form.

Nodule : A small, hard node that can be felt by touch (onchocerciasis, coenurosis, cysticercosis, myiasis).

Nomenclature : The system of naming things (e.g. organisms).

Nonphotochromogens : Slow-growing, nonpigmented mycobacteria.

Nonpolar : Possessing hydrophobic (water repelling) characteristics and not easily dissolved in water.

Nonpresumptive identification : Any of the methods pertaining to valid identification regardless of methods used to obtain identification. May include conventional biochemical testing, gas-liquid-chromotography, or various molecular biology techniques.

Nonselective media : Also known as enrichment media, it contains all of the necessary nutrients for the growth if all organisms. No inhibitory factors are contained in these media.

Nonsense mutation : A mutation that changes a sense codon into one which does not code for an amino acid.

Nonseptate : Lacking septa or cross-walls (coenocytic).

Nonsporulating : Does not produce spores.

Nonsterile sites : An anatomic site usually inhabited by (colonized with) members of the indigenous microflora (e.g. the skin, oral cavity, distral urethra, vagina, and gastrointestinal tract). (Improperly collected specimens form non sterile sites are unsuitable for anaerobic bacteriology.)

Nonsulfur purple bacteria : A group of phototrophic prokaryotes containing bacteriachlorophylls a or b which grow best as photohetertrophs and have a relatively low tolerance for hydrogen sulfide (H2S).

Nonsuppurative sequelae : Complications, caused by a previous attack a disease, that do not contain or drain pus.

Normotensive : Normal blood pressure; the usual readings in adults are seen between 90/50 and 150/90 Hg.

Northern Blot (NB) , uses techniques similar to the Southern blot described above. Messenger-RNA from the specimen is separated by electrophoresis and blotted to a specifically modified paper support to result in covalent fixing of the mRNA in the electrophoretic positions. Radiolabeled single-stranded DNA fragments complementary to the specific mRNA being sought are then hybridized to the bound mRNA. If the specific mRNA is present, the radioactivity is detected by autoradiography. The derivation of this technique from the Southern blot used for the DNA detection has led to the common usage of the term "Northen blot" for the detection of specific mRNA.

Nosocomial : Pertaining to or originating in hospital, as nosocomial infection.

Nosocomial infection : An infection occurring in a patient in a hospital or other healthcare facility in whom it was not present or incubating at the time of admission; or the residual of an infection acquired during a previous admission. Includes infections acquired in the hospital but appearing after discharge, and also such infections among the staff of the facility (Synonym hospital-acquired infection).

Nt : Neutralization.

Nuchal rigidity : Stiffness of the neck, often associated with meningeal infection.

Nucleic acid hybridization : Process by which the single-stranded probe unites with complementary DNA in an unknown sample.

Nucleic acid : A polymer of nucleotides, see also DNA and RNA.

Nucleic acid probe : Piece of labeled single-stranded DNA used to detect complementary DNA in clinical material or a culture and thus to specifically identify the presence in these materials of an organism identical to that used to make the probe.

Nucleocapsid : Name of viral particle that includes virus nucleic acid core enclosed in the protein capsid coat.

Nucleoid : The aggregated mass of DNA that makes up the chromosome of prokaryotic cells.

Nucleoside : A nucleotide without the phosphate group.

Nucleotide : A monomeric unit of nucleic acid, consisting of a sugar (ribose), a phosphate, and a nitrogenous base.

Nucleus : A cellular inclusion composed of chromatin; morphology often used to help identify intestinal protozoa (Entamoeba and Dientamoeba spp.).

Numerical taxonomy : The grouping by numerical methods of taxonomic units into taxa based on their character states.

Nutrient : A substance taken by a cell from its environment and used in catabolic or anabolic reactions.

Nutrient agar : The solid version of nutrient broth supplemented with agar.

Nutrient broth : A general-purpose liquid basal medium composed of, e.g., beef extract and peptone, which allows many types of microorganisms to grow.