Microbiology Terms Starting With T
Microbiology Glossary: T
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Thermophile
/ THER-moh-fyl / · Greek therme, heat; philos, loving
Thermophile is a microorganism that grows optimally at high temperatures, typically between 45 and 80 degrees Celsius, while hyperthermophiles grow best above 80 degrees Celsius.
Thermophiles stabilize proteins through tighter hydrophobic packing, additional ionic interactions, and chaperone systems that help prevent heat-induced unfolding. Their membranes resist high temperature through lipid compositions that maintain appropriate fluidity, including more saturated fatty acids in many bacteria and ether-linked isoprenoid lipids in many archaea. Thermus aquaticus, isolated from Yellowstone hot springs, produces Taq DNA polymerase, the heat-stable enzyme that made automated PCR practical.
Hyperthermophiles are a related but more extreme group, with organisms such as Pyrococcus furiosus growing near 100 degrees Celsius and some archaeal species growing above the normal boiling point of water under pressure.
Thermus aquaticus was isolated from a Yellowstone hot spring in 1966. Its DNA polymerase remains active after repeated heating to about 95 degrees Celsius, allowing PCR cycles to denature DNA without destroying the enzyme.
Are Enzymes Proteins? →High heat kills all microbes. Thermophiles grow best at temperatures that would injure or kill ordinary mesophilic microbes, although each species has its own upper limit.
Thermus aquaticus grows in hot spring environments where water temperatures commonly exceed 70 degrees Celsius. The organism grows best near 70 to 75 degrees Celsius, and its heat-stable polymerase enabled millions of laboratories to amplify DNA by PCR.
Toxoid
/ TOK-soyd / · Greek toxikon, poison; -oid, resembling
Toxoid is a bacterial toxin that has been chemically inactivated so it can no longer cause disease but still retains antigenic shape sufficient to stimulate protective antibody responses.
Toxoid vaccines are used when disease is caused mainly by a secreted bacterial toxin rather than by invasion of host tissues. Formaldehyde treatment alters the toxin enough to remove dangerous enzymatic or binding activity while preserving epitopes recognized by neutralizing antibodies. Diphtheria and tetanus vaccines use toxoids because antibodies that bind the toxins can prevent their effects even if bacteria enter the body.
Pertussis vaccines include inactivated pertussis toxin as one component, combined with additional Bordetella pertussis antigens to broaden protection. Booster doses are needed because antitoxin antibody concentrations decline over time.
Tetanus toxoid vaccination protects against the toxin, not against colonization of a wound by Clostridium tetani. That distinction is why wound cleaning and booster history both matter after injury.
Toxoid vaccines contain active toxin that causes the disease. Toxoids are inactivated toxins designed to provoke neutralizing antibodies without retaining toxic activity.
Immune System Fun Facts →The tetanus vaccine contains formaldehyde-inactivated tetanus toxoid derived from the neurotoxin of Clostridium tetani. Protective antitoxin levels are commonly maintained by booster vaccination about every 10 years in adults.
Transduction
/ tranz-DUK-shun / · Latin transducere, to lead across
Transduction is horizontal gene transfer in which a bacteriophage carries bacterial DNA from one bacterial cell to another.
Generalized transduction occurs when a lytic phage mistakenly packages a random fragment of host bacterial DNA instead of phage DNA and injects that fragment into a new cell. Specialized transduction occurs when a temperate prophage excises imprecisely from the bacterial chromosome and carries adjacent bacterial genes with it. Once transferred, the DNA may recombine with the recipient chromosome or be lost if it cannot replicate.
Transduction has shaped bacterial evolution by moving virulence genes, metabolic genes, and antibiotic resistance determinants, and it remains an important tool in bacterial genetics.
Some bacterial toxins are phage encoded. Diphtheria toxin, cholera toxin, and Shiga toxin are classic examples of virulence factors carried by bacteriophages or phage-related elements.
Bacterial Transduction →Bacterial transduction requires direct contact between two cells. A bacteriophage transfers DNA between bacteria, so donor and recipient cells do not need to touch.
Staphylococcus aureus can acquire virulence genes through phage-mediated transduction. In some strains, phages carry toxin genes that can convert a less harmful bacterium into a pathogen within a single gene-transfer event within a measurable window of 24 to 48 hours.
Transformation
/ tranz-for-MAY-shun / · Latin transformare, to change form
Transformation is horizontal gene transfer in which a bacterial cell takes up free DNA from its environment and incorporates or maintains that genetic material.
Natural transformation occurs in competent bacteria that express DNA-binding and uptake systems on their surface. Streptococcus pneumoniae, Haemophilus influenzae, Neisseria species, and Bacillus subtilis can take up environmental DNA and integrate homologous fragments into their chromosomes by recombination. In the laboratory, bacteria that are not naturally competent, such as many Escherichia coli strains, can be made artificially competent by calcium chloride heat shock or electroporation.
Transformation is foundational in molecular cloning because plasmid DNA introduced into bacteria can be replicated, selected, and purified for downstream genetic experiments.
Frederick Griffith discovered transformation in 1928 using Streptococcus pneumoniae. His experiment showed that a heritable factor from dead virulent bacteria could convert harmless bacteria into capsule-producing pathogenic cells.
Transformation means a bacterium changes shape. In microbiology, transformation means uptake of free DNA from the environment and acquisition of genetic traits encoded by that DNA.
Streptococcus pneumoniae can take up DNA released from nearby dead cells and recombine it into its chromosome. A DNA fragment only a few thousand base pairs long can change capsule type or antibiotic susceptibility if it carries the relevant genes.
Typhus
/ TY-fus / · Greek typhos (stupor, smoke)
Typhus is a group of acute febrile diseases caused by obligate intracellular bacteria of the genus Rickettsia, transmitted to humans by arthropod vectors including lice, fleas, and mites.
Rickettsiae invade the endothelial cells lining blood vessels, triggering vasculitis that produces the characteristic rash, fever, and organ damage seen across typhus diseases. Different species cause distinct clinical syndromes: Rickettsia prowazekii, spread by body lice, causes epidemic typhus, while Rickettsia typhi, spread by fleas, causes murine typhus. Epidemic typhus historically killed hundreds of thousands during wartime and famine, including an estimated 3 million deaths during World War I.
Diagnosis relies on serology or PCR, and doxycycline remains the treatment of choice for all rickettsial infections.
During Napoleon's retreat from Moscow in 1812, epidemic typhus killed more French soldiers than combat did, with some estimates placing louse-borne typhus deaths above 200,000 in that campaign alone.
How To Become An Infectious Disease Specialist? →Typhus and typhoid fever are the same disease with different names. Typhus is caused by Rickettsia bacteria transmitted by arthropods, while typhoid fever is caused by Salmonella enterica serovar Typhi and spreads through contaminated food and water.
Most Deadliest Bacterial Diseases →Epidemic typhus, caused by Rickettsia prowazekii, spreads through the feces of infected body lice rubbed into skin abrasions during scratching. Outbreaks have historically occurred in crowded, unsanitary conditions such as refugee camps, where louse infestation rates can exceed 80 percent of the population.