Glassware Used in the Microbiology Laboratory: Names and Uses

The microbiology laboratory relies on glassware to prepare and hold culture media, grow organisms, measure reagents, and prepare specimens for the microscope. Glass is preferred over plastic for most of this work because it withstands autoclaving and heat, resists most chemicals, and can be cleaned and reused without reacting with the contents.

The glass used in constructing the glassware is either borosilicate or soda-lime glass. The soda-lime is less tolerant to chemicals and has lesser hydrolytic resistance. So, soda-lime glassware is useful as a storage container. Borosilicate glass can tolerate chemicals like acids, halogens, and organic solvents. Only acids like hydrofluoric heated phosphoric acids or strong alkaline solutions can cause corrosion in the glass. That is why borosilicate glass is preferred over soda-lime glass.

In the microbiology laboratory specifically, the most-used glassware includes Petri dishes, test tubes and culture tubes, conical flasks, pipettes, graduated cylinders, McCartney bottles, microscope slides, and reagent bottles. The same glassware serves clinical, chemistry, and other biology laboratories, but the sections below focus on how each is used in microbiology.

Which Glassware for Which Microbiology Task

Beginners rarely struggle to name glassware; they struggle to know which piece a given task calls for. This is the quick map for a microbiology laboratory.

The rule that runs through the list: match the glassware to whether the task needs accuracy (measuring vessels), containment and sterility (culture and storage vessels), or just holding and mixing (beakers and flasks).

List of Glassware Used in Laboratory

The use of glassware is to store chemicals (liquid or solid), prepare reagents, mix chemicals, and perform different experiments.

Petri dish

Petri dish is glassware used in different biological laboratories, especially microbiology laboratories, to culture bacteria, fungi, or cell lines. The Petri dish is a shallow, circular, and transparent glassware invented by the scientist Richard Julius Petri. A transparent lid covers the base which is slightly larger in diameter.

Figure: Petri dish

See the full Petri dish article for types, uses, and how it is filled and handled.

Beaker

Beakers are wide, straight-sided containers with a pouring spout, used in microbiology for holding, heating, dissolving, and preparing media. Their printed graduations are approximate only, so a beaker is never used for accurate measurement.

Figure: Beaker

See the full beaker article for types and why it is not a measuring vessel.

Test tube

Test tubes are round-bottomed, open-topped borosilicate tubes used in microbiology to hold broth cultures, run biochemical tests, and collect or store samples. A capped version, the culture tube, is used to grow organisms without contamination, and a small inverted Durham tube inside a broth tube traps gas to detect fermentation. See the full Test tube article for types and how it differs from culture, centrifuge, and blood collection tubes.

Figure: Test tubes

Conical flask

A conical (Erlenmeyer) flask has a sloping conical body narrowing to a neck, so it can be swirled or shaken without spilling. In microbiology it is the standard vessel for growing organisms in broth culture, filled only partway and plugged with cotton so air exchanges while contaminants are kept out. It is also used to prepare and titrate.

Figure: Conical flask

See the full conical or Erlenmeyer flask article for why its shape suits culturing.

Graduated pipettes

Figure: Types of pipettes

Graduated pipettes are glassware with graduation marks for precise measurements. It has use in transferring liquids, drawing up samples or chemicals, and performing many more experiments. The pipettes are cylindrical tube-like structures. Some graduated pipettes have a bulb in between and a marking on the top part that indicates its volume capacity. Others have markings at an interval of 0.1 to 1 ml, depending on the pipette size.

Volumetric burette

Figure: Burette

A volumetric burette is a laboratory glassware with graduation marks that are commonly useful in titration. It has long cylindrical tube like body with slightly pointed bottom. There is a stopcock in the bottom of the burette to control the flow of the liquid. It is of two types; gas and liquid volumetric burette. The liquid falls due to gravity when the valve opens. In the case of a gas volumetric burette, the stopcock is at the top. The tube fills with water or mercury and connects to a reservoir with fluid at the base. The collection of gas occurs by displacement of the liquid.

Round bottom flask

As the name suggests, it is a flask with a round or circular base or bottom. These flasks are applicable for distillation and gas preparation in the laboratory. While working with a round bottom flask, a cork ring keeps it upright. Likewise, while performing the experiment stand holds it.

Figure: Round bottom flask

The material of RB is borosilicate glass and the flask is available in various sizes. The neck of the round bottom flask can be narrow, wide, or have a ground glass joint. Likewise, the number of necks can also vary from single, twin, and triple-necked.

Volumetric flask

A volumetric flask is laboratory glassware applicable for precise measurements at a specific temperature. The base of the volumetric flask is flat, and the bottom has pear like shape. The neck is long and cylindrical, with a calibrated marking for the volume it can measure.

Figure: Volumetric Flask

It is used to prepare precise molar (standard) solutions. Unlike a graduated cylinder, it has a single calibration line on the neck marking one exact volume, rather than a graduated scale, which is what makes it the most accurate volume-measuring glassware.

Microscope Slide

A slide or microscope slide is a thin piece of glass 3 by 1 inch in size. It is useful to hold samples and specimens for viewing under a microscope. The slide can be either plain or frosted at the end. The frosted glass slide is helpful in the preparation of blood smears.

Figure: Microscopic slide

The glass slide has staining purpose for biological specimens before observing them under the microscope. It is widely used in diagnostic, microbiological, botanical, and zoology laboratories.

Stirring rods

Figure: Glass stirring rods

Stirring or glass rods are laboratory glassware useful for mixing liquids. It is made up of solid borosilicate glass. Another use of a stirring rod is in spreading bacterial culture in solid growth media and conducting various tests. It is made up of a single piece of thin glass. It is usually 10-40 cm long and 0.5 cm in diameter.

Glass tube

Glass tubes are hollow cylindrical glassware useful for tubing purposes. It is also useful to make a delivery tube and transfer reagents.

Figure: Glass tube

A triangular file helps in cutting of the glass tube in the laboratory. Heating over the Bunsen burner helps bend the glass tube into the desired shape. Hence these are useful in the laboratory preparation of gases.

Graduated Cylinders

A graduated (measuring) cylinder is a tall, narrow vessel for measuring liquid volumes with reasonable accuracy, more accurate than a beaker or flask, less so than a volumetric flask. It is read at eye level at the bottom of the meniscus, and comes in class A and class B accuracy grades.

Figure: Graduated cylinder

See the full graduated or measuring cylinder article for how to read it and avoid parallax error.

Funnel

Figure: Different size of funnels

Funnels are laboratory glassware that is useful for filtering and transferring purposes. It has a narrow neck that allows only specific volumes of chemicals to flow through. Using filter paper helps in performing filtration in the laboratory. It is also useful for transferring fine-graded chemicals and liquids from one container to another. Using these kinds of funnel help avoid spillage in the laboratory. Other experiments where funnels are useful are separating mixed compounds by evaporation and condensation.

Reagent bottle

Figure: Reagent bottle

This bottle is constructed using borosilicate glass which is topped by a stopper. It is also called graduated or media bottles. The primary purpose of this bottle is to store reagents and solutions in the laboratory.

Retort

Figure: Glass retort

A glass retort is an airtight vessel useful for distillation purposes. It has a spherical or circular container with a narrow and downward-facing neck. The open end has a stopper made up of glass to make it airtight. The slim neck acts as a condenser during distillation.

Specific gravity bottle

Figure: Specific gravity bottle

The specific gravity, density, or relative-density bottle is useful in determining the densities of liquid. The density helps in calculating the specific gravity of the liquid. These are made up of glass and have caps to prevent evaporation. Some bottles have graduated necks that help in easy measurements. The size and shapes of this bottle vary widely.

McCartney bottle

Figure: McCartney Bottle

These are thick-walled glass bottles with aluminum or plastic screw caps, used in microbiology to store and autoclave culture media and reagents. The sealing cap keeps the contents sterile, and the bottle withstands repeated autoclaving. A closely related bottle, the universal or bijou bottle, serves the same purpose in smaller volumes.

Distillation flask

Figure: Distillation flask

A distillation or distilling flask is a glassware useful in the laboratory to separate two different liquids of different boiling points. The flask has round bottom for even heat dispersion, a long neck, and a sidearm for condensation. Flask with two or more necks is also available for complex distillation.

Flat bottom flask

Figure: Flat bottom flask

The construction of flat bottom flask is from borosilicate glass and are useful for boiling purposes. The shape of the vessels resembles the round bottom flask, except its base is flat instead of rounded. It has a similar neck to that of the round bottom flask.

Ebulliometer

Ebulliometer are glassware applicable to measure the temperature of different liquids by measuring the vapor-liquid equilibrium. There are two types of ebulliometer based on the principle used to measure the equilibrium; isothermal or isobaric ebulliometer. Swietoslawski ebulliometer, based on the isobaric method, has four major parts; boiler, thermowell, Cotterell pumps, and condenser. Besides the above parts, a stirring pump is present in an isothermal ebulliometer.

Abderhalden’s drying pistols

Figure: Abderhalden drying pistols

Abderhalden’s drying pistols are laboratory glassware useful to dry out or remove water molecules and impurities from the samples. Earl Abderhaldem provided a brief description of this pistol. The apparatus has two barrels; the inner one connects to the vacuum source with the help of a trap, and the outer barrel connects to the condenser and round bottom flask. This apparatus helps in the desiccation of heat-sensitive compounds when desiccators are ineffective.

Desiccators

A desiccator is an airtight container that keeps its contents dry using a desiccant such as silica gel, used in microbiology to store moisture-sensitive reagents and to cool heated crucibles without reabsorbing water.

Figure: Vacuum desiccators

See the full desiccator article for desiccants, the indicating color change, and handling.

Watch glass

Figure: Watch glass

It is a concave glass applicable in evaporating liquid in a chemistry laboratory by placing it on top of a beaker with boiling water. Watch glass is also known as clock glass. It is also useful to hold solid substances and as a cover for beakers.

Cleaning of Laboratory Glassware

Glass equipment is preferrable over plastic because it is reusable, durable, easy to clean, and appropriate for almost all experiments. So, cleaning laboratory glassware properly after every use is essential to avoid cross-contamination. Solids can deposit in the base of the glassware, small ions can firmly adhere to the surface of the glassware, or organic materials can bond with the glass. So, prepper solvent, surfactant, and cleaning methods are vital for reusing glassware.

General cleaning method

1. Cleaning general laboratory apparatus

Remove any remnant liquid or solid deposits in the glass and wipe any greasy substances using acetone and clean clothes. Wash the glassware gently in soapy water. Use a brush or cleaning pad to remove any residues. Rinse with water, followed by rinsing with deionized water. The deionized water forms a sheet in the glass. If this sheet is not present, follow an aggressive cleaning technique. In the case of burettes, pipettes, tubes, and volumetric flasks, rinse with the solution to be added thoroughly before use. Dry using acetone and dispose of it in the organic waste container.

1. Cleaning glassware with microbiological media

Remove the media from the container and dispose of it safely. Wash the glassware in warm soapy water. Rinse it with tap water. Using different methods of sterilization like using dry heat in an autoclave.

Mild cleaning method

Solid brittle deposits are removed by scraping using brushes, whereas soft deposits like grease will not entirely be removed by scrubbing. There are also areas in glass where brushes or clothes cannot reach.

Soak in gentle solvents like deionized water, dilute surfactants, concentrated weak acids, dilute phosphate, carbonates, or ammonia, and protein or saccharide solutions hydrolyzing enzymes for long periods can help.

The soaking action is benefitted from a simple mechanical process like stirring, shaking, and sonication.

Another method of cleaning is using organic solvents. Moistening a cloth with organic solvent for an easily accessible surface or agitating solvent inside the container is two methods commonly used. However, organic solvents are flammable and toxic, so proper ventilation, wearing gloves, and personal protective equipment is advised.

Aggressive cleaning method

Even after using organic solvents and mild cleaning methods, residues may not be removed. So removing adhered material is done either by oxidizing the residues or removing the top silicon layer.

Oxidizing contaminants from glassware is done by using various solutions like aqua regia, piranha solutions, fully concentrated sulfuric acids, pyrosulfuric acid, and chromic acid solution. Aqua regia is an aqueous nitric and hydrochloric acid solution in a 1:3 ratio.

The chromic acid solution is prepared by adding solid chromium (IV) oxide, potassium dichromate, or potassium chromate to the sulfuric acid. Piranha solution is a mixture of hydrogen peroxide the fully concentrated sulfuric acid. Fuming sulfuric acid has sulfur trioxide (10-20%) that makes pyrosulphuric acid.

The glass used to make the glassware has polysilicate solids and oxides. It also has sodium or potassium. The surface of the glass binds with hydroxyl and oxide, which is attached to silicon. Sometimes these surface functional groups bind to the contaminant, which is hard to remove with simple solvents. So, the silica layer is removed. The removal is done by soaking the glassware for a certain period in dilute hydrofluoric acid or base like potassium and sodium hydroxide in either ethanol or isopropanol.

References

1. Cheesbrough, M. (2006). District Laboratory Practice in Tropical Countries, Part 2 (2nd ed.). Cambridge University Press.
2. Tille, P. M. (2022). Bailey & Scott's Diagnostic Microbiology (15th ed.). Elsevier.
3. Willey, J. M., Sherwood, L. M., & Woolverton, C. J. (2021). Prescott's Microbiology (11th ed.). McGraw-Hill.
4. University of Wisconsin-Madison. Laboratory Glassware Cleaning. Retrieved from https://ehs.wisc.edu/wp-content/uploads/sites/25/2017/01/GlasswareCleaning.pdf