Types of Pipettes Used in the Microbiology Laboratory
Learn the types of pipettes used in microbiology — glass, micropipette, multichannel, automated, and calibrated — with a guide on choosing the right pipette for your procedure.
Every volume measurement in a microbiology laboratory begins with a pipette. A blood culture inoculated with an incorrect volume will grow poorly. An antibiotic dilution series prepared with the wrong pipette can produce a susceptibility result that is off by a factor of two. A PCR master mix assembled without filter tips risks nucleic acid contamination that invalidates the entire run. The choice of pipette is not a detail, it shapes the reliability of every result downstream.
Five categories of pipettes are used in microbiology laboratories: glass pipettes, micropipettes, multichannel pipettes, automated liquid handling systems, and pipette tips (the consumable that completes every micropipette). Understanding what each one is designed to do and where each one fails when misused, is essential laboratory knowledge.
Glass Pipettes
Glass pipettes are the oldest and most recognizable liquid handling instruments in the laboratory. They measure and transfer volumes in the milliliter range, making them the tool of choice when handling reagents, media, or specimens in volumes of 1 mL or above.
Three types are used routinely. Graduated pipettes (also called measuring pipettes) carry graduation marks along their length and allow partial volume delivery — useful when flexibility is needed. Within this category, Mohr's pipettes are drain-out types that do not require blowing out the last drop, while serological pipettes are blow-out types that require a final press of the bulb to deliver the full volume. Volumetric pipettes (non-graduated, also called bulb pipettes or transfer pipettes) are designed to deliver a single exact volume with high accuracy — ideal when one specific volume is needed repeatedly, such as in titrations or media preparation. Pasteur pipettes are the simplest form — narrow-tipped dropper-style pipettes used for approximate transfer, rinsing, or adding drops of reagent.
Glass pipettes require a pipette filler (rubber bulb or mechanical filler) for aspiration and dispensation. Mouth pipetting is unsafe and prohibited in any clinical or research laboratory.
Where glass pipettes fit in microbiology: preparing volumes of liquid media (10 mL, 5 mL), performing serial dilutions in test tubes, transferring serum in serological tests, and adding reagents to broth cultures.
Where glass pipettes do not belong: any volume below 1 mL requiring precision. Below 1 mL, measurement error becomes proportionally significant and a micropipette is the correct instrument.
For full detail on types, parts, handling technique, and Mohr's vs. serological differences, see: Glass Pipettes: Types, Handling, and Uses
Micropipette
The micropipette is the most widely used pipetting instrument in modern microbiology. It handles volumes in the microliter range — from as small as 0.2 µL up to 10,000 µL (10 mL in the largest P10000 models) — with a precision that glass pipettes cannot approach at these scales.
A micropipette works on the air displacement principle: pressing the plunger expels a defined volume of air, which draws an equal volume of liquid into the attached plastic tip when the plunger is released. The liquid never contacts the pipette body — only the disposable tip — which prevents cross-contamination between samples.
Micropipettes are manufactured in fixed volume and variable volume forms, and in a range of sizes designated by their maximum volume: P2 (0.2–2 µL), P20 (2–20 µL), P200 (20–200 µL), P1000 (100–1000 µL), and larger. Selecting the right size matters: pipetting at the extreme low end of a pipette's range (e.g., aspirating 5 µL with a P1000) introduces proportionally large errors. As a rule, always choose the smallest pipette whose range covers the target volume.
Where micropipettes fit in microbiology: PCR master mix preparation, antibiotic serial dilutions for MIC determination, ELISA plate preparation, DNA/RNA quantification, loading electrophoresis gels, and any procedure requiring µL-scale precision.
The most common error: pipetting at the wrong angle or failing to pre-wet the tip before aspirating volatile or viscous samples, leading to volume inaccuracy. For aqueous solutions, hold the pipette vertically (20° maximum tilt) during aspiration. For viscous or volatile samples, use reverse (backward) pipetting technique.
For full detail on parts, types, step-by-step technique, and error prevention, see: Micropipette: Parts, Types, and Uses
Multichannel Pipette
A multichannel pipette is structurally identical to a single-channel micropipette except that it carries 8, 12, 16, or up to 384 tip cones arranged in a row. All channels aspirate and dispense simultaneously, in one plunger movement.
The clinical microbiology application that makes multichannel pipettes indispensable is the microtiter plate — the 96-well plate format used in ELISA, minimum inhibitory concentration (MIC) determination, antimicrobial susceptibility testing by broth microdilution, and serological titrations. Without a multichannel pipette, filling 96 wells individually with a single-channel micropipette introduces both error and fatigue. An 8-channel pipette fills an entire column in one step; a 12-channel fills an entire row.
Multichannel pipettes are available in manual and electronic versions. Electronic multichannel pipettes add programmable dispensing modes — particularly useful for repetitive serial dilutions across a plate where consistent timing between wells matters.
Where multichannel pipettes fit in microbiology: ELISA plate loading, broth microdilution MIC testing, high-throughput serological assays, and any procedure using 96-well or 384-well plate formats.
Where they do not belong: single-tube work, streak plate inoculation, or any procedure where individual sample identity must be maintained between wells.
For full detail on parts, forward vs. backward pipetting technique, and calibration procedure, see: Multichannel Pipettes: Parts and Calibration
Automated Pipette (Liquid Handling System)
An automated liquid handling system replaces manual pipetting with robotic arms controlled by software. The operator enters the volume and plate layout; the instrument aspirates, transfers, and dispenses without further human intervention — a "walk-away" facility that frees laboratory staff during the run.
Automated systems operate on the same air displacement or positive displacement principles as manual pipettes, but at a scale and speed no human can match: a robotic liquid handler can process hundreds of samples per hour with CV (coefficient of variation) values below 1%. They are used in reference laboratories, blood bank automation, high-throughput drug screening, and large-scale PCR setup.
In resource-limited settings, automated pipetting systems are rarely the primary instrument — cost and maintenance requirements are significant. However, understanding their principle is important for students entering referral laboratory environments or research settings.
Where automated pipettes fit in microbiology: high-throughput ELISA processing, nucleic acid extraction automation, large-scale antimicrobial susceptibility screening, and blood bank automation.
For full detail on working mechanism, liquid handling system types, and applications, see: Automated Pipette: Liquid Handling System
Pipette Tips
Pipette tips are the disposable plastic attachments that connect to the tip cone of any micropipette or multichannel pipette. The liquid contacts only the tip (never the pipette body) which is what makes aseptic liquid transfer possible with a reusable instrument.
Choosing the right tip type is as important as choosing the right pipette. The key categories are:
Standard (non-sterile) tips are suitable for routine laboratory work — preparing reagents, handling non-infectious liquids, performing general dilutions. They are not certified free of RNase, DNA, or pyrogens.
Filter tips contain a hydrophobic polyethylene filter inside the tip shaft. If liquid or aerosol is accidentally drawn past the tip, the filter blocks it from entering the pipette barrel. Filter tips are mandatory for PCR work, RNA handling, and any procedure where carry-over contamination between samples is unacceptable.
Low-retention tips have a modified inner surface that reduces liquid adhesion. They are used for viscous samples, expensive reagents, or concentrated protein solutions where even a small residual volume left in the tip represents a significant loss.
Wide-bore tips have an enlarged opening. They are used for transferring cells, blood, or any sample containing particles or intact cells that a standard tip orifice would shear or clog.
The most important tip rule in clinical microbiology: never reuse a tip between specimens. A tip used on one sample and then dipped into another — even briefly, even apparently clean — transfers microorganisms. This is a contamination event, not a minor deviation.
For full detail on tip types, sterility classifications, and selection criteria, see: Pipette Tips: Types, Uses, and Criteria to Choose It
Pipette vs. Micropipette: The Most Common Confusion
Students and early-career laboratory workers frequently use "pipette" and "micropipette" interchangeably. They are not the same instrument.
| Feature | Glass Pipette | Micropipette |
|---|---|---|
| Volume range | 0.1 mL to 25 mL (milliliters) | 0.2 µL to 10,000 µL (microliters) |
| Precision | Moderate (±0.01–0.05 mL) | High (±0.5–1% of volume) |
| Liquid contact | Liquid enters the glass barrel | Liquid contacts only the disposable tip |
| Sterilization | Autoclavable | Tip is discarded; barrel is not autoclaved |
| Requires | Pipette filler/bulb | No additional equipment |
| Best for | mL-range volumes, media, reagents | µL-range volumes, PCR, ELISA, dilutions |
| Cross-contamination risk | Higher (liquid inside barrel) | Lower (disposable tip, liquid never enters barrel) |
The key distinction is scale: glass pipettes work in milliliters; micropipettes work in microliters. Attempting to measure 50 µL with a glass graduated pipette introduces an error large enough to ruin most molecular or serological procedures.
How to Choose the Right Pipette
When facing a pipetting task, three questions determine the correct instrument:
1. What volume do I need to transfer?
- ≥1 mL: glass pipette (graduated or volumetric depending on whether partial delivery is needed)
- 1 µL to 1000 µL: micropipette (select the model whose range includes your target volume)
- Multiple identical volumes into a plate simultaneously: multichannel pipette
- High-throughput repetitive transfers: automated liquid handling system
2. What level of precision does the procedure require?
- Approximate transfer (adding drops, rinsing): Pasteur pipette
- Standard laboratory work (media prep, serial dilutions): glass graduated pipette or standard micropipette
- Molecular work (PCR, gel loading, RNA quantification): micropipette with filter tips, calibrated instrument
3. What is the contamination risk?
- Routine non-infectious reagents: standard tips
- Infectious specimens, PCR work, RNA: filter tips mandatory
- BSL-2/3 specimens: disposable tips; consider electronic pipette to reduce repeated manual contact
Common Pipetting Errors and Their Consequences
Pipetting errors are among the most common sources of pre-analytical error in the microbiology laboratory — affecting culture results, susceptibility tests, and molecular assays before any test has technically been performed.
| Error | Consequence | Prevention |
|---|---|---|
| Wrong pipette size for the volume | Large proportional error — e.g., measuring 10 µL with a P1000 gives ±10% error | Always use the smallest pipette that covers the target volume |
| Reusing tips between samples | Cross-contamination — organisms or nucleic acids transfer between specimens | One tip per sample, no exceptions |
| Not pre-wetting the tip | First aspiration delivers less than target volume (tip surface absorbs liquid) | Aspirate and discard 2–3 times before the actual transfer for critical measurements |
| Pipetting at wrong angle | Air bubble aspiration or inaccurate volume | Hold micropipette vertically (≤20° tilt) during aspiration |
| Immersing tip too deeply | Liquid wets the outside of the tip and is carried into the next container | Immerse only 2–3 mm below the liquid surface |
| Using standard tips for PCR | Aerosol contamination enters the pipette barrel; PCR product contaminates future reactions | Filter tips are mandatory for all PCR work |
| Ignoring pipette calibration schedule | Systematic volume error accumulates undetected | Calibrate micropipettes every 3–6 months per laboratory SOP |
How to Remember
The volume scale rule — "Glass thinks in mL; micro thinks in µL." If your volume has "mL" in it, reach for a glass pipette. If it has "µL," reach for a micropipette. This prevents the most common selection error in student practical.
The tip rule — "The tip is the only thing that should touch the sample." The entire aseptic design of micropipetting rests on this principle. Liquid enters the tip; it never enters the barrel. A contaminated barrel contaminates every subsequent sample until the instrument is serviced.
Multichannel = plate work. If the container is a microtiter plate (96 wells or 384 wells), the multichannel pipette is the right instrument. If it is a tube, use a single-channel micropipette.
Mohr's vs. serological — "Mohr drains; serological blows." Mohr's pipettes drain to a point above the tip — the last drop is not delivered. Serological pipettes require blowing out to the tip to deliver the full volume (they have a blow-out ring at the top). Confusing them introduces a systematic delivery error.
Key exam facts in one table
| Topic | Key fact |
|---|---|
| Glass pipette volume range | mL scale (0.1 mL to 25 mL) |
| Micropipette volume range | µL scale (0.2 µL to 10,000 µL) |
| Micropipette working principle | Air displacement — liquid contacts only the tip, never the barrel |
| Mohr's pipette | Drain-out; last drop NOT delivered; graduation stops above tip |
| Serological pipette | Blow-out; full volume requires final press of bulb; blow-out ring at top |
| Volumetric (bulb) pipette | Delivers one fixed exact volume; highest accuracy among glass pipettes |
| Multichannel pipette | 8–384 channels; aspirates and dispenses simultaneously; used for 96-well plates |
| Filter tips — when mandatory | PCR, RNA work, infectious specimens — prevents aerosol entering barrel |
| Low-retention tips — when used | Viscous samples, expensive/concentrated reagents |
| Wide-bore tips — when used | Cells, blood, particulate-containing samples |
| Pre-wetting a tip | Aspirate and discard 2–3 times before actual transfer; prevents short-delivery on first aspiration |
| Calibration frequency | Every 3–6 months; required for ISO/accreditation compliance |
| Automated pipette advantage | Walk-away facility; handles >100 samples/hour; CV <1% |
| Most common student error | Using the wrong pipette size for the volume (e.g., P1000 for µL-scale precision work) |
References
- Clinical and Laboratory Standards Institute (CLSI). (2016). Clinical Microbiology Procedures Handbook (4th ed.). American Society of Microbiology. https://doi.org/10.1128/9781555818814
- Cheesbrough, M. (2006). District Laboratory Practice in Tropical Countries, Part 2 (2nd ed.). Cambridge University Press.
- Eppendorf AG. (2019). The Lab Pipetting Guide. Eppendorf. https://www.eppendorf.com/pipetting-guide
- ISO 8655-1:2022. Piston-operated volumetric apparatus — Part 1: Terminology, general requirements and user recommendations. International Organization for Standardization.
- Mahon, C. R., Lehman, D. C., & Manuselis, G. (2018). Textbook of Diagnostic Microbiology (6th ed.). Elsevier.
Frequently Asked Questions
What are the main types of pipettes used in a microbiology laboratory?
What is the difference between a pipette and a micropipette?
How do I choose the right pipette for a procedure?
When is a multichannel pipette used instead of a single-channel micropipette?
What is a calibrated loop and how does it differ from a pipette?
Tankeshwar Acharya, MSc (Medical Microbiology)
Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.