TA : Tube agglutination.

T cells : Lymphocytes involved in cellular immunity. See T lymphocyte.

Tachycardia : Rapid heartbeat, usually more than 100 beats per minute (trypanosomiasis).

Tachycardia : Increased heart rate (>100 beats per min in adults).

Tachypnea : Increase in respiratory rate (>20 breaths per min in adults).

Taxis : Movement toward or away from a stimulus.

Taxon (plural taxa) : A group into which related organisms are classified.

Taxonomy : The study of scientific classification and nomenclature.

TB : Tuberculosis; tuberculin; tubercle bacillus.

TCA : Trichloroacetic acid.

T cell receptor : The antigen-specific receptor on the surface of T lymphocytes.

Td : Tetanus, diphtheria.

TDA(2DE) : Two-dimensional electrophoresis.

T-DNA : The segment of the Agrobacterium Ti plasmid which is transferred to plant cells.

TDM : Therapeutic drug monitoring, testing serum for levels of antibiotics or other therapeutic agents.

Teichoic Acid : A polymer composed of alternating units of ribitol-phosphate or glycerol-phosphate to which may be attached various sugars and amino acids.

Teleomorph : The sexual or perfect state.

TEM : Transmission electron micrograph.

Temperate virus : A virus, which upon infection of a host, does not necessarily cause lysis but whose genome may replicate in synchrony with that of the host. See lysogen.

T-M : Thayer-Martin (agar plate).

Tenesmus : Painful, unsuccessful straining in an attempt to empty the bowels.

Tenosynovitis : Inflammation of the tough sheath surrounding a tendon.

Terminal : At the end.

Terminal spore : An endospore located at the end of the cell.

Termination1 :Stop of mRNA synthesis (i.e., transcription) at the terminator site.

Termination2 : Stop of protein synthesis (i.e., translation) at the stop codon.

Terminator : The site on a DNA sequence at which the process of transcription stops.

Teratogenic : Concerning agents which cause the abnormal development of an embryo, commonly resulting in fetal death or birth defects.

Tertiary structure : The final folded structure of a polypeptide that has previously attained secondary structure.

TGC : Third-generation cephalosporin.

Thallus : The vegetative growth or somatic phase of a fungus.

Therapy, antimicrobial : Treatment of a patient for the purpose of combating an infectious disease.

Thermoacidophilic : Growing best at high temperatures under acidic conditions.

Thermocline : Zone of water in a stratified lake in which temperature and oxygen concentration drop precipitously with depth.

Thermolabile : Adversely affected by heat (as opposed to thermostable, not affected by heat).

Thermophilic : Growing best at high temperatures (above 45 degrees C.).

Thiamine : A vitamin of the vitamin B complex, found in yeast, meat, and bran, and necessary for carbohydrate metabolism.

Thoracentesis : Drainage of fluid from the pleural space.

Thoracic : Pertaining to the chest cavity.

Thrill : Tremor felt on palpation of a hydatid cyst (Echinococcus granulosus).

Thrombocytopenia : A decrease in the numbers of platelets.

Thrombosis : Clotting within a blood vessel that may lead to infarction of the tissues supplied by that vessel.

Thrush : A form of Candida infection that typically produces white plaquelike lesions in the oral cavity.

Tick-borne disease : The diseases transmitted by ticks such as Rocky Mountain spotted fever, Q fever, and Lyme disease.

tid : 3 times a day.

Tinea : Ringworm or a skin disease occurring in different locations on the body due to a fungus. Example: Tinea pedis.

Tinnitus : Ringing or buzzing in the ear not resulting from an external source.

Tiplasmid : A conjugative plasmid present in the bacterium Agrobacterium tumefaciens which can transfer genes into plants.

Titer : Level of substance such as antibody or toxin present in material such as serum; reciprocal of the highest dilution at which the substance can still be detected.

T-lymphocytes (or T cells) : Thymus-derived lymphocytes important in cell-mediated immunity.

Tlg : Tetanus immunoglobin.

TMP/SMX : Trimethoprim-sulfamethoxazole.

TNTC : Too numerous to mention.

Tolerance : A form of resistance to antimicrobial drugs; of uncertain clinical importance. See tolerant.

Tonsillitis : Inflammation of one or more tonsils, usually the palantine tonsil.

TORCH : Toxoplasmosis, rubella, cytomegalovirus infection, and herpes infection; acronym used for illnesses or tests.

Toxic shock syndrome : Acute shock resulting from host response to an exotoxin produced by Staphylococcus aureus.

Toxigenicity : The degree to which an organism is able to elicit toxic symptoms.

Toxin : A microbial substance able to induce host damage.

Toxoid : A toxin modified so that it is no longer toxic but is still able to induce antibody formation.

TPI : Treponema palladium immobilization test, a test for antibodies against the agent of syphilis that uses live treponemes.

Trachoma : Serious eye infection caused by Chlamydia trachomatis; often leads to blindness.

Transbronchial biopsy : During bronchoscopy, the removal of a small piece of lung tissue through the walls of a bronchus (airway).

Transcription : Synthesis of an RNA molecule complementary to one of the two strands of a double-stranded DNA molecule.

Transduction : Moving genetic material from one prokaryote to another via a bacteriophage or viral vector.

Transfection : The transformation of a prokaryotic cell by DNA or RNA from a virus. Used also to describe the process of genetic transformation in eukaryotic cells.

Transfer RNA (tRNA) : A type of RNA that carries amino acids to the ribosome during translation; contains anticodon.

Transformation1 : Transfer of genetic information into a prokaryotic cell via free DNA.

Transformation2 : A process initiated by infection with certain viruses, whereby a normal animal cell becomes a cancer cell.

Transgenic : Used to describe genetically modified plants or animals containing foreign genes inserted by means of recombinant DNA techniques.

Translation : The synthesis of protein using the genetic information in a messenger RNA as a template.

Transmission of infectious agents : Any mechanisms by which an infectious agent is spread from a source or reservoir to a person. These mechanisms are as follows

Transpeptidation : The formation of peptide bonds between the short peptides present in the cell wall polymer, peptidoglycan.

Transplacental : Crossing the placenta; pertaining to any substance which passes from the mother to the fetus or vice versa.

Transposable element : A genetic element that has the ability to move (transpose) from one site on a chromosome to another.

Transposition : The movement of a piece of DNA around the chromosome, usually through the function of a transposable element.

Transposon : Genetic material from a plasmid that can move between plasmids or from a plasmid to a chromosome; so-called "jumping genes."

Transposon mutagenesis : Insertion of a transposon into a gene; this inactivates the host gene leading to a mutant phenotype and also confers the phenotype associated with the transposon gene.

Transtracheal aspiration : Passage of needle and plastic catheter into the trachea for obtaining lower respiratory tract secretions free of oral contamination.

Transudate : Similar to exudate but with low protein content.

Traveler diarrhea : Diarrhea often related to giardiasis, cryptosporidiosis, or Cyclospora spp.

Tricarboxylic acid cycle (= TCA cycle, citric acid cycle, Krebs cycle) : A series of metabolic reactions by which pyruvate is oxidized completely to carbon dioxide, also forming NADH, which allows ATP production.

Trichome : A trichome is a row of cells which have remained attached to one another following successive cell divisions. The cells in the trichome are usually separated by septa but some of the adjacent cells can communicate with one another via small pores (microplasmodesmata) which are not found in a simple chain of bacterial cells such as chains of streptococci. The cells of a trichome may or may not be covered by a common sheath. Trichomes are formed by many cyanobacteria and, e.g., by species of Beggiatoa.

Trismus : Spasm of the jaw muscles.

Trophozoite : Feeding, motile stage of protozoa.

Tropism : Preferred environment or destination. In viral infection, preference for a particular tissue site (rabies viruses have a tropism for neural tissue).

Truncate : Cut off sharply; ending abruptly with a flattened edge.

Trypanosome : Slender, flagellate protozoan found in the blood of humans (Trypanosoma spp.); also referred to as trypomastigote (new term).

TSI : Triple sugar iron (agar tube).

TSS : Toxic shock syndrome.

TTA : Transtracheal aspiration.

Tuberculate : Having knoblike projections.

Tuberculin test : A test for previous infection with Mycobacterium tuberculosis.

Tumor : Excessive tissue caused by uncontrolled cell growth.

Tympanic membrane : The ear drum.

Typing : Methods of grouping organisms, primarily for epidemiological purposes (e.g., biotyping, serotyping, bacteriophage typing, and the antibiogram).

Tzanck test : Stained smear of cells from the base of a vesicle examined for inclusions produced by HSV or VZV.