Microbiology Essentials: 300 Terms You Get Tested On

Most marks are lost between two organisms that look alike on one test and differ on another.

300 cardsLast updated 2026-08-31

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A negative Gram stain does not exclude mycobacteria, because their waxy wall resists the stain entirely. A positive result on an old culture does not confirm a gram-positive organism either, because older cells decolourise. Microbiology is full of tests that answer one question and quietly fail at another, and knowing which is which is most of the subject. This deck is 300 cards, one organism group, structure, process or technique per card, with the back giving the definition and, where it applies, a line on the organism or term it is confused with. The sections run from cell structure and staining through growth and metabolism, microbial genetics, control of microbes, viruses, fungi and parasites, and host interaction and immunity. No doses or treatment recommendations appear anywhere. The deck covers mechanisms of action, targets and resistance, which is what examinations test and what stays true regardless of local guidance. Once it is on a spaced-repetition schedule, the organisms you can already separate stop coming back and the pairs you keep confusing return until they stop being guesswork.

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What's inside

Showing 100 representative cards from the full 300-card deck.

Front	Back
Prokaryotic cell — what is it?	A cell without a membrane-bound nucleus or organelles. Prokaryotic does not mean simple. Prokaryotes have highly organised internal structure.
Coccus — what is it?	A spherical bacterial cell. Arrangement is a clue to identity, so it must be recorded along with shape.
Spirillum and spirochete — what is it?	Two kinds of helical bacterial cell. The difference in motility structure is what separates them, not the degree of coiling.
Peptidoglycan — what is it?	The polymer that gives bacterial cell walls their strength. It is found in bacteria but not in archaea, fungi or human cells.
Lipopolysaccharide — what is it?	A molecule in the outer membrane of gram-negative bacteria. It is released mainly when the cell dies, not secreted during growth.
Acid-fast cell wall — what is it?	A wall containing large amounts of waxy mycolic acid. These organisms stain poorly by the Gram method, so a negative Gram result does not exclude them.
Capsule — what is it?	A well-organised polysaccharide layer outside the cell wall. A capsule is not a slime layer, which is loose and easily washed away.
Flagellar arrangements — what is it?	The pattern of flagella on a bacterial cell. Arrangement is a taxonomic feature and does not indicate how fast the cell moves.
Fimbriae — what is it?	Short hair-like appendages used for attachment. Fimbriae are for attachment, not motility, and are far more numerous than flagella.
Endospore — what is it?	A dormant, highly resistant structure formed inside certain bacteria. An endospore is a survival structure, not a means of reproduction.
Germination — what is it?	The return of an endospore to an actively growing cell. A germinating cell loses its resistance, which is the basis of some sterilisation methods.
Nucleoid — what is it?	The region of a prokaryotic cell containing the chromosome. It is a region, not an organelle, and has no defined boundary.
Plasmid — what is it?	A small circular DNA molecule separate from the chromosome. Plasmids are usually not essential for growth, which is why they can be lost.
Simple stain — what is it?	A staining method using one dye to make cells visible. It gives no information about cell wall type or internal structure.
Gram stain — what is it?	The most widely used differential stain in bacteriology. Over-decolourisation makes gram-positive cells appear gram-negative.
Endospore stain — what is it?	A stain that reveals endospores within or outside cells. Unstained spores appear as clear areas in a simple stain, which can be mistaken for artefacts.
Flagella stain — what is it?	A method that thickens flagella so they become visible. Flagella are too thin to see with ordinary stains, so absence in a simple stain proves nothing.
Brightfield microscopy — what is it?	Microscopy in which specimens appear dark against a bright background. Unstained cells have too little contrast to be seen well this way.
Phase contrast microscopy — what is it?	Microscopy that converts differences in refractive index into contrast. It is not the same as darkfield, which relies on scattered light alone.
Electron microscopy — what is it?	Microscopy using a beam of electrons instead of light. Specimens must be processed and cannot be viewed alive.
Immersion oil — what is it?	Oil placed between the slide and the highest power objective. Using the oil objective without oil gives a blurred image that cannot be focused.
Binary fission — what is it?	The division of one bacterial cell into two. It produces two cells of equal size, unlike budding in some yeasts.
Bacterial growth curve — what is it?	The pattern of population change in a closed culture. The curve describes a batch culture, so a continuous culture behaves differently.
Stationary phase — what is it?	The period when new cells balance dying cells. The total count stays level while the viable count begins to fall.
Continuous culture — what is it?	A system in which fresh medium is added and culture removed continuously. It requires balancing flow rate against growth rate, or the culture washes out.
Obligate aerobe — what is it?	An organism that requires oxygen for growth. It grows only at the surface of a liquid medium tube.
Aerotolerant anaerobe — what is it?	An organism that does not use oxygen but is not harmed by it. It grows evenly throughout a tube, unlike a facultative anaerobe.
Psychrophile — what is it?	An organism that grows best at low temperatures. It can spoil refrigerated food, so refrigeration slows but does not stop all growth.
Thermophile — what is it?	An organism that grows best at high temperatures. Thermophiles do not cause human infection, since body temperature is too low for them.
Acidophile and alkaliphile — what is it?	Organisms adapted to low and high pH. Most bacteria are neutrophiles, so extreme pH values inhibit them.
Halophile — what is it?	An organism that requires high salt concentrations. Salt-tolerant organisms are not necessarily halophiles, which require salt rather than tolerate it.
Complex medium — what is it?	A medium whose exact chemical composition is not known. Batch to batch variation makes it unsuitable for precise nutritional studies.
Differential medium — what is it?	A medium that makes colonies of different organisms look different. A medium can be both selective and differential, and the two roles must be identified separately.
Streak plate — what is it?	A method for obtaining isolated colonies from a mixture. A colony arises from one cell only if separation was successful.
Colony forming unit — what is it?	A unit representing one viable cell or clump that produces a colony. A clump of cells produces one colony, so counts underestimate cell number.
Direct microscopic count — what is it?	Counting cells in a known volume under the microscope. It counts living and dead cells together unless a viability stain is used.
Chemoheterotroph — what is it?	An organism using organic compounds for both energy and carbon. It contrasts with autotrophs, which use inorganic carbon.
Photoautotroph — what is it?	An organism using light for energy and carbon dioxide for carbon. Photosynthetic bacteria do not all produce oxygen.
Glycolysis — what is it?	The pathway converting glucose into pyruvate. It is the shared starting point for both fermentation and respiration.
Fermentation end products — what is it?	The organic compounds produced by different fermentation pathways. Detecting acid production requires an indicator, since the product itself is invisible.
Anaerobic respiration — what is it?	Respiration using an inorganic molecule other than oxygen as the final acceptor. It is respiration, not fermentation, because an electron transport chain is used.
Catabolism and anabolism — what is it?	The breakdown of molecules for energy and the building of new ones. The two occur simultaneously, not in alternating phases.
Bacterial chromosome — what is it?	A single circular DNA molecule carrying the essential genes. A few bacteria have linear or multiple chromosomes, so the circular form is typical rather than universal.
R plasmid — what is it?	A plasmid carrying genes for antimicrobial resistance. Transfer of one plasmid can confer resistance to several unrelated agents at once.
Bacterial DNA replication — what is it?	Copying of the circular chromosome from a single origin. One origin serves the whole chromosome, unlike in eukaryotes.
Spontaneous mutation rate — what is it?	The frequency of mutations arising without an external agent. A culture of billions of cells will contain mutants even without any mutagen.
Frameshift mutation — what is it?	An insertion or deletion that shifts the reading frame. It has a far larger effect than a substitution at the same position.
Ames test — what is it?	A test using bacteria to screen chemicals for mutagenic activity. It detects mutagenicity, which correlates with but does not prove carcinogenicity.
Replica plating — what is it?	A technique transferring colony patterns from one plate to another. It was used to show that mutations arise before exposure to the selecting agent.
Horizontal gene transfer — what is it?	The movement of genetic material between organisms other than by descent. It differs from vertical transfer, which passes genes to offspring.
Competence — what is it?	The physiological state allowing a cell to take up external DNA. Laboratory treatments can force competence in species that lack it naturally.
Generalised transduction — what is it?	Transduction in which any part of the host chromosome can be transferred. Any gene can move, unlike in specialised transduction.
Conjugation — what is it?	The transfer of DNA between bacteria through direct contact. Conjugation requires cell contact, unlike transformation.
Transposon — what is it?	A DNA segment that can move to a new location in a genome. It moves within and between DNA molecules, so it is not confined to one chromosome.
Integron — what is it?	A genetic element that captures and expresses gene cassettes. It is a capture system, not a mobile element in itself, although it often sits on one.
Intrinsic resistance — what is it?	Resistance that is a natural property of a species. It is not acquired, so it is present in every member of the species.
Efflux pump — what is it?	A membrane protein that expels compounds from the cell. A single pump can produce resistance to several drug classes at once.
Genome sequencing in microbiology — what is it?	Determining the complete DNA sequence of an isolate. Carrying a resistance gene does not always mean the gene is expressed.
Sterilisation — what is it?	The removal or destruction of all microorganisms including endospores. Sterile is an absolute term. Almost sterile is not sterilisation.
Sanitisation — what is it?	Reducing microbial numbers to a level judged safe by public health standards. The standard is a defined reduction, not the elimination of all organisms.
Decimal reduction time — what is it?	The time required to kill ninety percent of a population. Microbial death is exponential, so no finite time gives absolute certainty of sterility.
Moist heat sterilisation — what is it?	The use of steam under pressure to kill microorganisms. Water must reach every surface, so packing and loading matter as much as time.
Dry heat sterilisation — what is it?	Sterilisation using hot air rather than steam. It is used for materials that steam would damage, such as powders and oils.
Desiccation — what is it?	The removal of water to prevent microbial growth. Many organisms survive drying and revive when moisture returns.
HEPA filtration — what is it?	High efficiency filtration of air to remove particles and organisms. It removes organisms from air but does not kill them, so filters remain contaminated.
Phenolics — what is it?	A group of disinfectants that disrupt membranes and denature proteins. Their strong odour and tissue irritation limit where they can be used.
Aldehydes — what is it?	Agents that cross-link proteins and nucleic acids. Their toxicity and irritant vapour require careful handling and ventilation.
Antimicrobial drug — what is it?	A substance used to treat infection by inhibiting or killing microorganisms. Selective toxicity is hardest to achieve against eukaryotic pathogens.
Nucleic acid synthesis inhibitors — what is it?	Agents that block bacterial DNA replication or transcription. Single point mutations in the target enzyme readily confer resistance.
Disc diffusion susceptibility test — what is it?	A method measuring the zone of inhibition around an impregnated disc. A larger zone does not always mean a better clinical choice, since criteria differ by agent.
Virus — what is it?	An obligate intracellular agent consisting of nucleic acid in a protein coat. A virus is not a cell and cannot be cultured on agar.
Naked virus — what is it?	A virus without a lipid envelope. Alcohol-based agents are less reliable against these viruses.
Attachment — what is it?	The binding of a virus to a specific receptor on the host cell. Binding requires a matching receptor, which is why viruses show tissue preferences.
Eclipse period — what is it?	The interval when no infectious virus can be recovered from the cell. The virus is present but disassembled, so absence of particles does not mean absence of infection.
Bacteriophage — what is it?	A virus that infects bacteria. The phage particle itself does not enter the cell in many cases.
Prophage — what is it?	A phage genome integrated into a bacterial chromosome. It can carry toxin genes, so its presence may change the pathogenicity of the host.
Latency — what is it?	The persistence of a virus in a cell without producing new particles. The absence of symptoms does not mean the virus has been cleared.
Antigenic drift — what is it?	Gradual change in viral surface proteins from accumulated mutations. It produces small yearly changes rather than a sudden new virus.
Prion — what is it?	An infectious protein particle containing no nucleic acid. It resists heat and chemicals that destroy conventional organisms.
Fungal cell structure — what is it?	The features of a eukaryotic fungal cell. Fungal walls contain no peptidoglycan, so cell wall agents used against bacteria do not work.
Dimorphic fungus — what is it?	A fungus that grows as a mould or a yeast depending on temperature. Culture at the wrong temperature gives a misleading appearance.
Protozoa — what is it?	Single-celled eukaryotic organisms, many of which are motile. They are not fungi or bacteria and require different culture approaches.
Helminth — what is it?	A parasitic worm. Helminths are multicellular animals, so they are not microorganisms in the strict sense.
Definitive host — what is it?	The host in which a parasite reaches sexual maturity. The definitive host is not necessarily the host that suffers most.
Biological and mechanical vectors — what is it?	Vectors in which the pathogen develops and those that merely carry it. A mechanical vector transports the pathogen unchanged, as on its body surface.
Ova and parasite examination — what is it?	Microscopic examination of stool for parasite stages. Shedding is intermittent, so several specimens may be needed.
Normal microbiota — what is it?	The community of microorganisms that normally live on and in the body. Its presence in a specimen does not indicate infection.
Pathogenicity and virulence — what is it?	The ability to cause disease and the degree of that ability. Pathogenicity is a yes or no property, while virulence is a matter of degree.
Adhesion — what is it?	The attachment of a pathogen to host cells. Without adhesion most pathogens are removed before they can multiply.
Coagulase — what is it?	An enzyme that causes plasma to clot. It is also a laboratory test result, and a positive test is used for identification.
Exotoxin — what is it?	A protein toxin secreted by a living bacterium. Exotoxins are produced by both gram-positive and gram-negative organisms.
Neurotoxin — what is it?	An exotoxin acting on the nervous system. The site of action is remote from where the organism grows.
First line of defence — what is it?	The physical and chemical barriers that prevent entry. Breaching these barriers, as by a catheter, bypasses the strongest defence.
Inflammation — what is it?	The tissue response to injury or infection. Inflammation is protective, although excessive inflammation causes damage.
Adaptive immunity — what is it?	The specific defence that develops after exposure to an antigen. Its slower onset is why innate immunity must hold the infection at first.
Cell-mediated immunity — what is it?	Immunity mediated by T cells acting directly on infected cells. It does not involve antibodies, so antibody tests may not reflect it.
Antibody — what is it?	A protein produced by B cells that binds a specific antigen. Antibodies rarely kill organisms directly, and mostly mark them for other mechanisms.
Active and passive immunity — what is it?	Immunity produced by the person's own response and immunity transferred from elsewhere. Passive immunity acts immediately but fades as the transferred antibodies are cleared.
Incidence and prevalence — what is it?	The number of new cases and the total number of cases at a time. A long-lasting disease has high prevalence even with low incidence.
Healthcare-associated infection — what is it?	An infection acquired in a healthcare setting. The organisms responsible are often part of the patient's own flora.

Frequently asked

What is in each section of the deck?

Cell structure and staining has 50 cards, growth and metabolism 50, microbial genetics 45, control of microbes 45, viruses, fungi and parasites 55, and host interaction and immunity 55, for 300 in total. Every card carries section and subtopic tags, so you can drill only staining or only immunity.

Is this a clinical microbiology deck?

No. It covers the science that clinical practice rests on, including virulence factors, resistance mechanisms and susceptibility testing, but it contains no doses, no regimens and no treatment advice. Clinical decisions depend on local guidance and on a patient in front of you, neither of which belongs on a flashcard.

Who is it aimed at?

Students taking an introductory microbiology course, including those on nursing, laboratory science and biology programmes. The vocabulary is standard across those courses, so the deck transfers even where the syllabus order differs from the section order used here.

Can I import the whole deck on the free plan?

Yes. Importing a saved deck runs no new AI generation and does not use your AI allowance, so the free plan imports all 300 cards. You can study, edit and delete them afterwards.

Will importing it twice create duplicates?

No. Cards you already have are skipped and only cards added in a revision come through. Including re-imports after deleting it, one official deck can be imported three times per account.

Can I use it on the web and in the mobile app?

Yes. The deck is added to your account rather than to a device, so the same cards and the same progress are there on the web, on iOS and on Android.

Can I edit the cards after importing?

Yes. Imported cards are yours: you can edit both sides, delete cards you do not need, change tags, and move cards to another deck.