Microbiology Terms and Terminology with Definitions

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 45⁰C 

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 45⁰C 

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

References

1. World of Microbiology and Immunology K. Lee Lerner and Brenda Wilmoth Lerner, Editors. Volumes 1 and 2. 2003. The Gale Group, Inc. 27500 Drake Road Farmington Hills, MI, 48331-3535.
2. Prescott’s Microbiology, 12th Ed. 2019. Joanne Willey, Kathleen Sandman and Dorothy Wood. McGraw Hill Publication.
3. Textbook of Microbiology by Surinder Kumar. 2012. Jaypee Brothers Medical Publishers (P) Ltd. ISBN : 978-93-5025-510-0
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5. Textbook of Microbiology and Immunology. 2nd Eds. By Subash Chandra Parija. Elsevier publication.
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9. Microbiology from A to Z explained – Micropia – Micropia
10. Microbiology Words – 400+ Words Related to Microbiology (relatedwords.io)