Microbiology Terms and Terminology with Definitions

Microbiology Terms
Microbiology Terms

Microbiology Terms from the Letter A

Abiotic = Non-living

Abiogenesis = Generation of life from abiotic components 

Actinomycetes/Actinobacteria = Group of filamentous bacteria 

Adhesion = Attachment of microorganisms over biotic/abiotic surface

Agar = Polymer of galactose sugar (agarose) and agaropectin derived from algae and used to solidify culture media 

Agar Medium = Solid/semi-solid culture medium containing agar

Agar Diffusion = Diffusion of molecules via matrix in agar medium 

Agarose Gel = A semi-solid matrix formed by the solidification of agarose; mainly used in the differentiation of proteins, and nucleic acids 

Aerobes = Microorganisms requiring atmospheric oxygen for respiration/survival

Anaerobes = Microorganisms that can survive in absence of atmospheric oxygen

Aerotolerant =  Anaerobes that can tolerate atmospheric oxygen 

Antibiotics = Medicines/chemicals used against bacteria/bacterial infections

Antibiotic Resistance = ABR; the ability of bacteria to escape the effect of antibiotics 

Antifungal = Medicines/chemicals used against fungi/fungal infections

Antifungal Resistance = Ability of fungi to escape the effect of antifungals

Antimicrobials = Medicines/chemicals used against microorganisms/microbial infections

Antimicrobial Resistance = AMR; the ability of microorganisms to escape the effect of antimicrobials

Anthelmintic = Medicines/chemicals used against helminths/helminthic infections

Antiprotozoal = Medicines/chemicals used against protozoa/protozoan infections

Antiparasitic = Medicines/chemicals used against parasites/parasitic infections

Antiviral = Medicines/chemicals used against viruses/viral infections

Antiviral Resistance = Ability of viruses to escape the effect of antivirals

Antiseptics = Antimicrobials applied over living tissues 

Archaea = Domain of prokaryotic organisms, similar morphology to bacteria but unique biochemistry against microorganisms 

Aseptic = Sterilized/free from microbes 

Asepted = Microbial cell lacking septa  

Agglutination = Clumping together 

Antigen = Foreign body capable of activating the immune system

Antibody = Glycoprotein produced by the immune system against a specific antigen 

Antagonistic = Showing inhibitory/cidal response to another 

Amphitrichous = Bacteria with a single flagellum at each end

Atrichous = Lacking flagella

Alpha (α)-hemolytic = Microorganisms partially disrupting RBCs giving greenish zone of hemolysis

Attenuate = To reduce the virulence of a pathogen

Autoclave = Sterilizing equipment that uses a pressurized hot stem; to sterilize using an autoclave

Autotroph= Organism that can synthesize their own food

ATP = Adenosine Triphosphate; energy currency of cell/stored form of energy in a living system

AST = Antimicrobial Sensitivity (Susceptibility) Testing; Procedure to test the sensitivity of antimicrobials

ATCC = American Type Culture Collection; Organization storing and providing standard microorganisms 

ABR = Antibacterial Resistance 

AMR = Antimicrobial Resistance

Microbiology Terms from the Letter B

Bacteria = A domain of prokaryotic, microscopic, unicellular organism

Bacterial Culture = Bacteria grown in a culture medium 

Bacteriology = Study of Bacteria 

Bacteriophage = Viruses that can infect bacteria

Bacillus = Rod-shaped bacterium

Bacteremia = Presence of bacteria in the blood

Bacteriuria = Presence of bacteria in urine

Bacterial = Caused/Related to bacteria

Bactericidal = Substance having the capacity to kill bacteria 

Bacteriostatic = Substance having the capacity to inhibit bacterial growth/multiplication

Basal medium = Culture medium with minimum nutrition that is enriched with highly nutritious substance to make enrichment/special media 

Bio-hazard = Biological components that are hazardous 

Broth = Liquid culture medium

Broad-spectrum Antibiotics = Antibiotics acting against a broad range (both Gram-positive and negative) of bacteria

Biochemical Tests = A set of tests to identify the biochemical characteristics of a microorganism 

Biochemical Characterization = Classification of microorganisms based on biochemical characters 

Biofilm = A thick film/aggregate of bacteria formed within a thick slimy extracellular matrix

Bioluminescent bacteria = Bacteria emitting light  

Blood Agar = Enriched culture medium containing blood

Blood Borne Infections = Infections transmitted through blood

Buffer = Solution that resists change in pH of a solution

BSC = Bio-safety cabinet 

Microbiology Terms from the Letter C

Capsule = Gelatinous extracellular layer covering bacteria, usually made of polysaccharide

Capsulated = Having capsule as the outermost layer

Capsid = Protenious  capsular shell enclosing viral genomes

Carbon source = Nutrient/component in a culture medium that provides carbon for microbial growth

Chain = Arrangement of microbial cells in form of a line

Chitin = Protein in the cell wall of the fungus 

Chromosome = Bacteria genomic DNA 

Cidal effect = Killing of bacteria/microorganisms  

Cilia = Fine hair-like appendages in Eukaryotes 

Ciliates = Protozoans having cilia 

Clone = Offspring of a single microbial cell

Cluster = Arrangement of microbial cells in a group 

Cryopreservation = Preservation of microbial cells in very low temperature 

Coagulase = Microbial enzyme that can clot plasma

Coagulase Test = Test to detect the ability of a microbe to produce coagulase 

Coliform = A group of Gram-negative bacilli found in the feces of vertebrates 

Colony = Visible group of microbial cells developed after microbial culture  

Complex Media = Media that supports the growth of broad-range of microbes 

Compound microscope = Light microscope that uses two sets of lenses 

Conjugation = Transfer of bacterial DNA by direct contact between two bacterial cells 

Contamination = Introduction of unwanted microorganisms 

Contaminated growth = Microbial culture with unwanted/uninoculated microorganisms 

Co-culture/Consortia = Mutual growth of two different species/genera of microbes in a single culture

Commensals = Normal flora  

Coulter counter = Device used to count microbial cells in a suspension 

Culture = To grow/multiply microorganisms; culture medium with grown microorganisms

Culture = Isolated and multiplied single species of microorganisms 

Culture Medium = Nutritious substance that supports the growth of microorganisms 

CFU = Colony formation unit; microbial cell/cells that form a single colony

Microbiology Terms from the Letter D

Decontamination = Making a sample/object sterile; removal of alive microorganisms 

Decomposers = Microorganisms that degrade complex organic matters into a simpler form 

Desiccation = Removal of water 

Diatoms = Microscopic, unicellular algae

Dinoflagellates = Unicellular algae with two flagella 

Diffusion = Spreading over a matrix of medium or gel 

Diplococcus = Arrangement of microbial cells in a group of two

Diphtheroid = Commensal bacteria morphologically similar to C. diphtheriae   

Dilution = Suspension of microorganisms or chemicals in a certain proportion 

Direct Microscopy = Counting of microbial cells in a sample using a microscope 

Disinfectant = Chemicals that kill/inhibit microorganisms (used in inanimate surfaces) 

Disinfection = Removal of microorganisms (mainly from the inanimate surface)

Disc/Disk = A small circular (usually 6 mm) filter-paper piece mostly used to carry antibiotics or chemicals for test 

DNA = Deoxyribonucleic acid 

Microbiology Terms from the Letter E

Enterobacterales /Enteric bacteria = Bacteria found in GI-tract; Members of Enterobacteriaceae  

Electrophoresis = Technique to separate macromolecules and nucleic acids using electricity over agarose gel

Endotoxin = Pyrogenic lipopolysaccharide mostly within cell-wall of Gram-negative bacteria; toxin within the bacterial cell  

Enterotoxin = Exotoxin affecting intestinal cells 

Exotoxin = Toxin released outside the microbial cell 

Enteric fever = Typhoidal/Paratyphoid fever 

Eubacteria = A domain of prokaryotes including true bacteria 

Extremophiles = Organisms thriving in extreme environments 

ELISA = Enzyme Linked Immunosorbent Assay; a detection technique 

ETC = Electron Transport Chain

ESBL = Extended Spectrum -Lactamase; a type of -Lactamase enzyme 

Microbiology Terms from the Letter F

Facultative Aerobe = Aerobic microorganism that can even survive in anaerobic condition

Facultative Anaerobe = Anaerobe that can even survive in presence of oxygen 

Fermentation = Anaerobic breakdown of organic substance (sugar) into alcohol, acid, or gas by microorganisms 

Flagella = Hair-like protruding appendages in the microorganism that provide motility 

Flagellates = Microbes having flagella 

Filamentous = Long thread-like morphology of microorganisms 

Fimbriae = Fine proteinous appendages smaller than flagella 

Fluorescence Microscope = Microscope that uses a fluorescent dyed sample and sample emitted light to form a magnified image of the sample

Fungus = Kingdom including eukaryotic organisms with chitin as a component of cell wall

Microbiology Terms from the Letter G

Gene = Functional unit of DNA encoding for a particular trait

Genetic Analysis = Study of genetic materials

Gene mapping =Determining the position of genes in DNA

Genetically Engineered/Modified = Organisms whose genes are artificially modified 

Genera/Genus = A taxonomic category below a family that constitutes phylogenetically or morphologically similar species 

Genotype = Complete genetic constituent of a microorganism 

Germinal Stage = Stage of microbes in which they can replicate  

Germs = Microorganisms that can cause disease/infection; pathogens

Germ Theory = A principle that defines the relation between germs and disease  

Gliding Bacteria = Bacteria having gliding motility 

Globulins = Antibodies  

Gram Stain = A compound stain composed of Crystal Violet, Iodine, and Safranin used to differentiate bacteria 

Gram Staining = Staining technique that uses Gram stains 

Gram Positive = Bacteria that stain purple or violet after Gram staining 

Gram Negative = Bacteria that stain red or pink after Gram staining 

Growth Medium = Culture medium

Microbiology Terms from the Letter H

Halophiles = Salt-loving microorganisms 

Heterotrophs = Organisms that depend on others for food/nutrition 

Hazard = A great risk

Hemolysis = Breakdown of RBCs

Hemolytic Bacteria = Bacteria capable of breaking down RBCs

Host = Living body that provides nutrition to parasite

Hyphae = Thin, elongated, and nucleated branching fungal cells either septate or aseptate/non-septate   

Microbiology Terms from the Letter I

Immunogenic = Capable of stimulating the immune system

Immunogen = Antigen/infectious agent

Immune = Resistant 

Immunity = Resistance against infections

Immunization = Vaccination

Immunodeficiency =Lack of ability of the immune system to resist infections

Immune compromised = Suppressed immune system

Immunoglobulin = Antibodies

In Vitro =In laboratory; outside the natural habitat

In Vivo =In natural habitat

Indicator Organisms/Indicator = Microorganisms that indicate the presence of certain pathogens without actually isolating the pathogens 

Infection =Invasion of tissue by one or more pathogenic organisms and establishment of disease 

Infectious =Capable of causing infection

Inhibition = Interference and suppression of microbial growth/multiplication 

Inhibitory zone = A zone of inhibition formed around an antimicrobial substance 

Invasive =Capable of penetrating tissue layer

Inoculation = Introduction (transfer) of microorganisms 

Inoculate = To introduce/transfer microorganisms into something

Inoculating Loop = Tool with a loop at its end that is used to transfer microorganisms

Inoculating Wire =Tool with a straight wire that is used to transfer microorganisms 

Inoculum = Substance/sample with microorganisms to be tested  

Incubate = To keep/maintain in ambient conditions for microbial growth

Incubator = Device that maintains ambient conditions for microbial growth 

Incubation = Keeping inoculated media in ambient temperature and atmospheric conditions for microbial growth

Microbiology Terms from the Letter J

Junk DNA = DNA whose function is not known 

Microbiology Terms from the Letter K

Koch’s Postulates = Criteria to define a microorganism as causative of a disease 

Microbiology Terms from the Letter L

LAB = Lactic Acid Bacteria; bacteria producing lactic acid

Laminar Air Flow Cabinet/Hood=Device used to prevent contamination of and from sample   

Lancefield Classification = Classification scheme of Streptococcus spp. based on serological characteristics (surface antigens)

Latent = Existing without showing symptoms 

Latent Infection = Infection without observable symptoms

Lethal = Potential of taking life

Lethal Dosage (LD)= Amount of toxin that is enough to kill

Lichen = Obligate association of fungus and algae

Light Microscope = Microscope that uses visible light

Liquid Media = Broth/culture medium in a liquid state

Lysogeny = A type of life cycle of viruses (bacteriophage) using viral genome integrated bacterial DNA for multiplication/replication 

LPS = Lipopolysaccharide 

Microbiology Terms from the Letter M

McFarland Standard Solution = Solution of 1% barium chloride and 1% sulfuric acid at a fixed concentration 

Methanogens = Microorganisms producing methane gas during metabolism

Metabolism =Chemical reactions occurring inside living cells 

Mesophilic = Microorganisms whose ambient growth temperature is between 20 to 450

Microbiology = Study of microorganisms

Microbes = Microorganism

Microbial = Relating to microorganisms 

Microorganisms = Organisms that are visible only under a microscope 

Microscopy = Use of microscope to produce a magnified image of microscopic objects 

Microscope = Device used to form a highly magnified image of tiny objects for clear visualization 

Microbial flora = Microorganisms normally living in/on our body surface without causing disease

Microaerophilic = Microorganism that can survive in presence of a very low concentration of oxygen

Mold = Filamentous fungi/fungi with mycelial body 

Monoclonal = Originating from a single cell

Mutation = Sudden change in gene

Mutant = Organism with certain mutation making it different from than parents 

Mycelium = Elongated branching structure of hyphae

Mycology = Study of fungus 

MDR = Multi drug resistant 

MIC = Minimum inhibitory condition; minimum concentration of antimicrobial required to inhibit microbial growth

MBC = Minimum bactericidal concentration; minimum concentration of antibiotics necessary to kill bacteria 

MPN = Most probable number; a technique used to estimate viable microbial concentration in a sample

Microbiology Terms from the Letter N

Negative Bacteria =Gram negative bacteria 

No Growth = Lack of microbial multiplication and formation of visible colonies 

Non-selective Media = Culture media that support the growth of a wide range of media and produce similar colonies for different microbial species 

Non-culturable Bacteria = Bacteria that can’t be cultured in vitro in culture media 

Nosocomial = Hospital born/acquired  

Microbiology Terms from the Letter O

Obligate Parasite = Parasite that can’t live outside the host 

Obligate Aerobe = Organisms that can’t survive without oxygen 

Obligate Anaerobe = Organism that can’t survive in presence of oxygen

Oncogene = Gene capable of triggering mutation in the cell causing the development of cancer 

Oxidizing bacteria = Bacteria that oxidize certain components/substrate

Microbiology Terms from the Letter P

Parasite = Organism that depends on the living body for survival 

Parasitic = Depending on others for survival

Pasteurization = A technique of sterilization by rapidly heating and cooling the sample (liquid)

Pathogen = Organism that has the potential to cause infection

Pathogenic = Capable of causing disease

Pathogenicity = Capacity of the pathogen to cause disease

Pathogenesis = Order of development of a disease

Pathology = Study of disease 

Pathovar = Bacterial strain with similar characteristics except in their pathogenicity 

Petri Dish/Petri plate = Transparent cylindrical plate for containing culture media in which microorganisms are cultured

Phage = Bacteriophage

Phenotype = Observable morphological characteristics

Phenotypic = Based on observable characters

Photosynthetic Microorganisms = Microbes capable of conducting photosynthesis 

Pili = Short, thin, flexible, and soft bacterial appendages 

Pipette = Instrument used to measure and transfer small volume of liquid sample

Plasmid = Circular, double stranded, extrachromosomal DNA of bacteria 

Presumptive Test = Biochemical test to presume the presence of specific microorganisms in a sample

Probiotics =Viable microorganisms that are consumed to promote gut flora and gut health 

Prions = Small proteinaceous infective agents lacking nucleic acid

Pseudohyphae = Arrangement of yeast cells giving the appearance of a hyphae

Psychrophilic =Microorganisms thriving in cold

PCR =Polymerase Chain Reaction; a molecular technique to amplify nucleic acid

Microbiology Terms from the Letter Q

Qualitative Analysis/Test = Test to identify microorganisms in a sample

Quantitative Analysis/Test = Tests to identify and count the number of microorganisms in a sample

Quorum Sensing = Coordinated behavior/communication in microbial/bacterial community 

Microbiology Terms from the Letter R

Rapid Test = Tests used for quick identification of an unknown microorganism

Recombinant DNA = A chemically combined DNA containing DNA portions of different organisms  

Replication = Production of exact copies 

Respiration = Breakdown of an organic molecule (glucose)inside the cell producing ATP

Restriction Enzyme = Bacteria enzymes that cleave DNA at specific sites

Reverse Transcription = Process of the formation of DNA from RNA

RNA = Ribonucleic acid

RIA = Radioimmunoassay 

Microbiology Terms from the Letter S

Sample = Specimen/Materials from where microorganisms are supposed to be isolated

Selective Media = Media that selectively allow the growth of certain species of microorganisms while inhibiting the growth of the others

Septate =Divided

Serovar = Serotype; bacterial or viral strains with all the characters same but different antigens and stimulate a host’s immune system for the production of different antibodies 

Sheathed Bacteria = Bacteria arranged in filaments covered with a mucilaginous sheath

Slime Layer = An outer slimy layer in some bacteria made of polysaccharides, glycolipids, and glycoproteins. 

Species = A taxonomic category below the genus that can interbreed

Spirochetes = Spirally twisted-shaped bacterial group

Sporulation = Process of formation of spore

Spore = A thick-walled dormant stage of bacteria or fungi that can develop into a viable individual  

Sterilization = Process of removing (killing) all viable microorganisms 

Strain = Variants of the same species resulted due to certain variations/mutations in their genes 

Sub-type = Strain 

Sub-species = A taxonomic category below species including organisms that are morphologically distinct but can interbreed 

Staph = Staphylococcus

Strep= Streptococcus

SEM = Scanning Electron Microscope

Microbiology Terms from the Letter T

Taq Polymerase = Bacterial polymerase enzyme derived from Thermus aquaticus 

Thermophiles = Organisms that thrive in temperatures above 450C

Thermotolerant = Organisms whose ambient temperature is below 450C but can even survive and grow in temperatures above 450

Transcription = Process of formation of RNA from DNA

Translation = Process of formation (decoding) proteins from RNA

Transformation = Transfer of genetic material (DNA) directly from one bacterium to another through a cell membrane

Transduction= Introduction of foreign gene/DNA into bacterial DNA via virus

Transgenic = Organism whose genetics have been altered by incorporation of foreign gene/DNA segment

Transmission = Transfer of pathogens from one host to another

Transposition = Transfer of DNA/gene from one site to another

TEM = Transmission Electron Microscope 

Microbiology Terms from the Letter U

Urease Test = Biochemical test to detect the production of urease enzyme by bacteria 

Microbiology Terms from the Letter V

Variants = Subtype (usually of viruses and bacteria) that are genetically different but the genetic difference is not sufficient to classify as a separate strain  

Viruses = Self-replicating obligate parasitic infectious agents having only one type of nucleic acid as their genome 

Virulence = Microorganism’s ability to damage host’s cells/components 

Virulence factor = Molecules secreted by or expressed within pathogens that enable them to establish infection 

Vaccine = Medicine that stimulates the body’s immune response to protect and prevent infection 

Viable = Living

Virology = Study of viruses 

Microbiology Terms from the Letter W

Winogradsky Column = An instrument acting as a self-supporting ecosystem used to study microbial diversity of an environment 

Microbiology Terms from the Letter X

Xanthophyta = Yellow-green algae 

Microbiology Terms from the Letter Y

Yeasts = Single-celled fungi

Microbiology Terms from the Letter Z

ZN-stain = Staining procedure used to stain acid-fast bacteria (Mycobacteria)

Zoonoses = Infections transmitted by animals 

Zone of Inhibition = A clear zone without visible microbial growth around antimicrobial component


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About Author

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Prashant Dahal

Prashant Dahal completed his bachelor’s degree (B.Sc.) Microbiology from Sunsari Technical College, affiliated with Tribhuvan University. He is interested in topics related to Antimicrobial resistance, the mechanism of resistance development, Infectious diseases (Pneumonia, tuberculosis, HIV, malaria, dengue), Host-pathogen interaction, Actinomycetes, fungal metabolites, and phytochemicals as novel sources of antimicrobials and Vaccines.

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