Tamil Nadu HSE First Year Microbiology flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Koch's postulates

Four criteria linking a microorganism to a disease: found in all diseased hosts, isolated in pure culture, reproduces disease when inoculated, and re-isolated from the experimental host.

Germ theory of disease

The concept, established by Pasteur and Koch, that specific microorganisms cause specific infectious diseases, replacing the earlier theory of spontaneous generation.

Chemolithotrophy

A nutritional mode in which microorganisms obtain energy by oxidising inorganic compounds such as ammonia, nitrite, sulphur, or iron, while using carbon dioxide as carbon source.

Peptidoglycan

A polymer of alternating N-acetylglucosamine and N-acetylmuramic acid cross-linked by short peptides, forming the rigid cell wall of bacteria and the target of penicillin.

Gram-negative outer membrane

An additional lipid bilayer outside the thin peptidoglycan layer, containing lipopolysaccharide that acts as endotoxin and porins that allow small molecules to pass.

Bacterial endospore

A dormant, highly resistant structure formed by Bacillus and Clostridium during nutrient depletion; it is dehydrated, contains dipicolinic acid, and survives boiling but not autoclaving.

Viral capsid

The protein coat, built from subunits called capsomeres, that surrounds and protects the viral nucleic acid and helps the virus attach to and enter host cells.

Generation time

The time required for a microbial population to double in number during exponential growth; it varies widely among species and depends on nutrients and conditions.

Selective medium

A culture medium containing substances that inhibit growth of unwanted microorganisms while allowing the desired organism to grow, such as MacConkey agar for Gram-negative bacilli.

Facultative anaerobe

An organism that grows best with oxygen but can also grow without it by using fermentation or anaerobic respiration, such as Escherichia coli and Staphylococcus aureus.

Serial dilution plate count

A viable counting method in which a sample is diluted in steps, plated, incubated, and colonies counted; results are expressed as colony-forming units per millilitre.

Plasmid

A small, self-replicating extrachromosomal circular DNA molecule in bacteria that can carry genes for antibiotic resistance, fertility, or metabolic functions.

Conjugation

Transfer of DNA from one bacterium to another through direct cell-to-cell contact via a sex pilus, typically moving a plasmid from an F-positive to an F-negative cell.

Transformation

Uptake of naked DNA from the environment by a competent bacterial cell, which may then express the newly acquired genes, as shown in Griffith's pneumococcal experiments.

Lac operon

An inducible operon in Escherichia coli whose structural genes for lactose metabolism are switched on only when lactose is present and glucose is scarce.

Point mutation

A change in a single DNA base pair that may be silent, cause a missense substitution, or create a nonsense stop codon, altering the protein produced.

Autoclave

Equipment using saturated steam under pressure, usually 121 degrees Celsius at 15 psi for 15 to 20 minutes, to sterilise media and glassware including bacterial spores.

Pasteurisation

Controlled heating of a liquid such as milk, either 63 degrees Celsius for 30 minutes or 72 degrees Celsius for 15 seconds, that kills pathogens without sterilising the product.

Bacteriostatic agent

A substance that inhibits the growth and multiplication of bacteria without killing them, so removal of the agent allows surviving cells to resume growth.

Membrane filtration

Passage of a liquid or gas through a filter with pores about 0.22 micrometres, physically removing bacteria and fungi but not reliably removing viruses.

Immunoglobulin G

The most abundant antibody class in blood and tissue fluid, the only one crossing the placenta, and the main mediator of long-term humoral immunity.

Passive immunity

Protection acquired by receiving preformed antibodies from another source, such as maternal IgG across the placenta or antiserum injection, giving rapid but short-lived defence.

Type IV hypersensitivity

A delayed, cell-mediated reaction mediated by sensitised T lymphocytes rather than antibody, exemplified by the tuberculin skin test and contact dermatitis.

Exotoxin

A heat-labile protein toxin secreted by living bacteria, such as tetanus or cholera toxin, which is highly specific and can be neutralised by a specific antitoxin.

Acid-fast staining

A staining method using carbol fuchsin with heat or phenol, then acid-alcohol decolourisation, that detects mycobacteria such as Mycobacterium tuberculosis in sputum.

Widal test

A tube agglutination test that detects antibodies against Salmonella typhi antigens in serum, used as an aid in diagnosing enteric fever.

Nitrogen fixation

Conversion of atmospheric nitrogen gas into ammonia by microorganisms such as Rhizobium, Azotobacter, and cyanobacteria, using the oxygen-sensitive enzyme nitrogenase.

Biological oxygen demand

The amount of dissolved oxygen consumed by microorganisms while decomposing organic matter in a water sample, used as an indicator of organic pollution.

Bioremediation

Use of microorganisms or their enzymes to break down or remove pollutants such as oil, pesticides, and heavy metals from soil, water, or air.

Food intoxication

Illness caused by a preformed toxin in food, produced by organisms such as Staphylococcus aureus or Clostridium botulinum, rather than by infection with living bacteria.

Probiotic

A live microorganism, commonly Lactobacillus or Bifidobacterium, that when consumed in adequate amounts confers health benefits by improving intestinal microbial balance.

Gram staining

A differential stain using crystal violet, iodine, alcohol decolouriser, and safranin counterstain that divides bacteria into purple Gram-positive and pink Gram-negative groups.