0.5 Glossary  (Page 4/18)

D

• dacryocystitis inflammation of the lacrimal sac often associated with a plugged nasolacrimal duct
• daptomycin cyclic lipopetide that disrupts the bacterial cell membrane
• darkfield microscope a compound light microscope that produces a bright image on a dark background; typically a modified brightfield microscope
• death phase (decline phase) phase of the growth curve at which the number of dying cells exceeds the number of new cells formed
• decimal reduction time (DRT) or D-value amount of time it takes for a specific protocol to produce a one order of magnitude decrease in the number of organisms; that is, death of 90% of the population
• decolorizing agent a substance that removes a stain, usually from some parts of the specimen
• deeply branching bacteria bacteria that occupy the lowest branches of the phylogenetic tree of life
• definitive host the preferred host organism for a parasite, in which the parasite reaches maturity and may reproduce sexually
• degeneracy redundancy in the genetic code because a given amino acid is encoded by more than one nucleotide triplet codon
• degerming protocol that significantly reduces microbial numbers by using mild chemicals (e.g., soap) and gentle scrubbing of a small area of skin or tissue to avoid the transmission of pathogenic microbes
• degranulation release of the contents of mast cell granules in response to the cross-linking of IgE molecules on the cell surface with allergen molecules
• dehydration synthesis chemical reaction in which monomer molecules bind end to end in a process that results in the formation of water molecules as a byproduct
• deletion type of mutation involving the removal of one or more bases from a DNA sequence
• Deltaproteobacteria class of Proteobacteria that includes sulfate-reducing bacteria
• denatured protein protein that has lost its secondary and tertiary structures (and quaternary structure, if applicable) without the loss of its primary structure
• dendrites branched extensions of the soma of a neuron that interact with other cells
• dengue fever mosquito-borne viral hemorrhagic disease; also known as breakbone fever
• dental calculus calcified heavy plaque on teeth, also called tartar
• dental caries cavities formed in the teeth as a result of tooth decay caused by microbial activity
• deoxyribonucleic acid (DNA) double-stranded nucleic acid composed of deoxyribonucleotides that serves as the genetic material of the cell
• deoxyribonucleotides DNA nucleotides containing deoxyribose as the pentose sugar component
• dermatophyte any fungus of the genera Microsporum, Epidermophyton, or Trichophyton , which feed on keratin (a protein found in skin, hair, and nails) and can cause cutaneous infections
• dermis the second layer of human skin, found between the epidermis and the hypodermis
• descriptive epidemiology a method of studying a disease outbreak using case histories, contact interviews, medical information, and other sources of information
• desensitization injections of antigen that lead to production of antigen-specific IgG molecules, effectively outcompeting IgE molecules on the surface of sensitized mast cells for antigen
• desiccation method of microbial control involving the removal of water from cells through drying or dehydration
• desquamation peeling and shedding of outermost skin
• diapedesis process by which leukocytes pass through capillary walls to reach infected tissue; also called extravasation
• diaphragm a component of a microscope; typically consists of a disk under the stage with holes of various sizes; can be adjusted to allow more or less light from the light source to reach the specimen
• differential interference-contrast microscope a microscope that uses polarized light to increase contrast
• differential media media that contain additives that make it possible to distinguish bacterial colonies based on metabolic activities of the organisms
• differential staining staining that uses multiple dyes to differentiate between structures or organisms
• diffraction the changing of direction (bending or spreading) that occurs when a light wave interacts with an opening or barrier
• dikaryotic having two separate nuclei within one cell
• dimorphic fungus a fungus that can take the form of a yeast or a mold, depending on environmental conditions
• dioecious refers to sexually reproducing organisms in which individuals have either male or female reproductive organs (not both)
• diphtheria serious infection of the larynx, caused by the toxigenic bacterium Corynebacterium diphtheriae
• diploid having two copies of each chromosome
• direct agglutination assay assay that can be used to detect the agglutination of bacteria by the action of antibodies in patient serum
• direct antihuman globulin test (DAT) another name for a direct Coombs’ test
• direct contact transmission movement of a pathogen between hosts by physical contact or transfer in droplets at a distance less than one meter
• direct Coombs’ test assay that looks for antibodies in vivo against red blood cells caused by various types of infections, drug reactions, and autoimmune disorders
• direct ELISA enzyme-linked immunoabsorbent assay in which the antigens are immobilized in the well of a microtiter plate; only a single antibody is used in the test
• direct fluorescent antibody (DFA) test FA technique in which the labeled antibody binds to the target antigen
• direct hemagglutination assay test that determines the titer of certain bacteria and viruses that causes clumping of red blood cells
• direct microscopic cell count counting of cells using a calibrated slide under a light microscope
• direct repair (light repair or photoreactivation) light-dependent mechanism for repairing pyrimidine dimers involving the enzyme photolyase
• disaccharide one of two monosaccharides linked together by a glycosidic bond
• disease any condition in which the normal structure or function of the body is damaged or impaired
• disinfectant antimicrobial chemical applied to a fomite during disinfection that may be toxic to tissues
• disinfection protocol that removes potential pathogens from a fomite
• disk-diffusion method a technique for measuring of the effectiveness of one or more antimicrobial agents against a known bacterium; involves measuring the zone(s) of inhibition around the chemical agent(s) in a culture of the bacterium
• dispersion the separation of light of different frequencies due to different degrees of refraction
• disulfide bridge covalent bond between the sulfur atoms of two sulfhydryl side chains
• DNA gyrase (topoisomerase II) bacterial topoisomerase that relaxes the supercoiled chromosome to make DNA more accessible for the initiation of replication
• DNA ligase enzyme that catalyzes the formation of a covalent phosphodiester linkage between the 3’-OH end of one DNA fragment and the 5’ phosphate end of another DNA fragment
• DNA packaging process in which histones or other DNA binding proteins perform various levels of DNA wrapping and attachment to scaffolding proteins to allow the DNA to fit inside a cell
• DNA polymerase class of enzymes that adds nucleotides to the free 3’-OH group of a growing DNA chain that are complementary to the template strand
• DNA primers short, synthetic, single-stranded DNA fragments of known sequence that bind to specific target sequences within a sample due to complementarity between the target DNA sequence and the primer; commonly used in PCR but may be used in other hybridization techniques
• DNA probe a single-stranded DNA fragment that is complementary to part of the gene (DNA or RNA) of interest
• DNAse pathogen-produced nuclease that degrades extracellular DNA
• dosage amount of medication given during a certain time interval
• double immunodiffusion see Ouchterlony assay
• doubling time the time it takes for the population to double; also referred to as generation time
• droplet transmission direct contact transmission of a pathogen transferred in sneezed or coughed droplets of mucus that land on the new host within a radius of one meter
• drug resistance ability of a microbe to persist and grow in the presence of an antimicrobial drug
• dry-heat sterilization protocol that involves the direct application of high heat
• dura mater tough, outermost membrane that surrounds the brain
• dynein motor proteins that interact with microtubules in eukaryotic flagella and cilia
• dysentery intestinal inflammation that causes diarrhea with blood and mucus
• dysuria urination accompanied by burning, discomfort, or pain