Common Terms and Definition in Microbiology Laboratory

man woman technology looking
Photo by Edward Jenner on

Common Terms and Definition in Microbiology Laboratory

Click the drop-down box to reveal answer.

aerosol – a spray of live microbes ejected from sputtering

brightfield microscope – a microscope which the general background or field of view is bright while dense specimens appear darker objects; used for stained materials

capsule – thick layer of substance found on the surface of some bacteria that inhibits phagocytosis by white blood cells

capsule stain – involves the process of negative staining the slide and staining the cytoplasm of the bacteria making the capsule only the colorless structure which appears as a light halo around the bacteria

carbol fuchsin – the primary stain used in acid fast staining

citrate test – detects species of bacteria that survive on citrate as its carbon source

 coagulase – a bacterial enzyme which brings about the coagulation of blood or plasma and is produced by disease-causing forms of staphylococcus

 colony – visible mass of microorganisms originating from a single mother cell

compound microscope – microscope with two magnifying lens

 conclusion – logical judgment or analysis we make from our results

 condenser – lens system in microscope whose function is to focus the light onto the specimen

 conjugation – joining of two bacteria or unicellular organism for the transfer of genetic material by direct cell to cell contact or by bridge like connection called sex pilus

 contamination – the presence of undesirable microorganism that accidentally gets into a culture

 control group – the group in the experiment that does not receive treatment; used to compare how the experimental group do

 controlled variable – the factors in the experiment that we control and keep the same

 crystal violet – primary stain used in Gram staining

 darkfield microscope – creates the effect of a negative image; field of view is dark while cells and other objects are lit up; used to observe live, motile cells

 decolorizer – removes the primary stain from the gram-negative bacteria making it colorless

 dependent variable – the variable being tested, observed, and measured

 differential medium – a medium with diagnostic test built into it that changes color with different species of microbes

 differential staining – procedure that will dye different kinds of bacteria in contrasting color

 double blind – a type of experiment which neither the subjects nor the experimenters know which subjects are in the test and control groups

 electron microscope – a microscope that uses beam of electron rather than beam of light to observe a specimen

 endemic – when a disease prevalence is fairly stable in a location

 epidemic – occurs when a disease is spreading rapidly in a particular population

 ethyl alcohol – the decolorizer used in Gram staining

 fluorescence – the ability of a substance to absorbed UV light and emit back the light as a visible color

 Gram’s iodine – mordant used in Gram staining

 HCG – is a hormone that prevents menstruation from occuring during pregnancy

 Hfr cell – a bacterial cell with conjugative plasmid integrated into its chromosomal DNA

 immunocompromised – means more susceptible to infections

 independent variable – also called the experimental variable; anything that can be changed or manipulated

 lysozyme – an enzyme that dissolves the chemical bond between the NAG and NAM within the backbone of the peptidoglycan molecule in gram-positive bacteria

 malachite green – primary stain in spore staining

 methylene blue – counterstain used in acid fast staining

 microbial hot spots – warm and moist areas where the number of microorganisms is usually the highest

 minimum inhibitory concentration – lowest concentration of drug which prevent visible growth of bacteria

 mordant – a substance which causes the primary stain to become more tightly bound to the cell

 negative stain – a stain which involves staining the background of the slide

 nosocomial infection – infectious disease acquired during hospitalization

 nutrient agar – a general purpose medium that will support growth of many common bacteria

 ocular lens – also called eyepiece; the top lenses of the microscope which you look through

 ocular micrometer – also called the microscopic ruler inscribed into the eyepieces on the microscope

 opsonin – an antibody which binds to foreign microbes making them susceptible to phagocytosis

 pandemic – occurs when a disease is spreading globally or over one continent

 parfocal – means when one lens is focused, the others are also focused

 phase contrast microscope – a microscope that increases the contrast between cells or portions of cells that vary only slightly in density; used to observe unstained bacterial cells

 pour plate – is made by inoculating melted agar with bacteria and then pouring the agar into an empty petri plate to harden, thus the microbes are distributed evenly throughout the agar; creates an evenly distributed lawn of bacteria to be use for phage typing

 pseudopodia – extension of cytoplasm use for movement; also called false feet

pure culture – a medium growing with only one intended species of microorganism

 refraction – the bending of light

 normal flora – microorganisms that live naturally and permanently in various areas of the human body

 resolving power – defined as the closest distance two objects can be where you can still see them as separate objects

 result – refers to the actual data that you collect such as the number of colonies

R-plasmid – is a plasmid in bacteria that contains the antibiotic resistant gene

 Sabouraud agar – medium that are slightly acidic and have extra glucose; also used for fungal growth; used to check fungal spores in the air

 safranin – the counter-stain used in Gram staining

 scanning electron microscope – a microscope that reflects beam of electrons off the exterior of the specimen; produces 3D view of specimen’s surface

 selective medium – a medium that only allows certain species of microbes to grow and inhibits others

 simple microscope – microscope with single magnifying lens

 simple staining – defined as a procedure that stains all cells with the same color

 Snyder test – measures the amount of acid produced by normal flora in a medium containing sugar

 sporadic – occurs when a disease is infrequent and in scattered location

 stage – the platform below the objective lenses of a microscope used to hold the slide

 stage micrometer – term typically referring to a slide that comes with a known scale on its surface

 sterile – a term which means free of bacteria or living things

 streak plate – is performed by spreading an inoculum of bacteria across the surface of an agar plate in such a way as to produce isolated colonies

 Streptococcus mutans – oral bacteria involve with the development dental caries or tooth decay

 super-infection – second infection with microbial agent that is resistant to the treatment used against the first infection

 synthetic medium – medium made from scratch with every single ingredient defined and listed separately

 thermal death point – minimum temperature required to kill a bacteria with a given amount of time

 thermal death time – time required to kill a bacteria at a particular temperature

 transduction – is the process by which foreign DNA is introduced into a cell by a virus or viral vector

 transformation – is a process of horizontal gene transfer by which some bacteria take up foreign genetic material from the environment

 transient flora – microbes that are temporary and can be removed by handwashing

 transport medium – is a medium used to transport microbes from one place to another and limits the overgrowth of microbes


Alderson, Gary D. Microbiology Experiments and Lab Techniques 14th Edition. Palomar College. Fountainhead Press. Accessed November 26, 2019.

Leave a Reply