Automated Specimen Processing and Inoculation in Microbiology

Two technologists streak the same urine specimen onto two plates. After incubation, one plate shows clean, well-separated colonies ready to pick; the other is a confluent smear at the center with too few isolated colonies to work up.

Nothing was done wrong; manual streaking simply varies from hand to hand and hour to hour. An automated specimen processor removes that variation, streaking every plate the same way, which is why it has become the front end of the modern microbiology laboratory.

What an automated specimen processor does

An automated specimen processor is an instrument that carries out the first hands-on steps of culture-based testing: it takes the specimen, plants (inoculates) it onto the appropriate culture plates, and streaks it to spread the organisms for isolated colonies.

These are the steps a technologist would otherwise do by hand with a loop, and they are repetitive, high-volume, and surprisingly variable between operators.

The best-known example is the WASP (Walk-Away Specimen Processor), and similar processors form the front end of the integrated systems described later.

Whatever the brand, the instrument does the same job: it replaces the manual loop-and-hand streaking of each plate with a consistent, machine-controlled inoculation, so that every plate is streaked the same way regardless of who is on shift or how busy the bench is.

The two jobs: planting and streaking

The instrument does two things in sequence, and it helps to keep them distinct.

Planting (inoculation) is placing a measured amount of the specimen onto the plate. Automated processors handle liquid specimens most easily, urine, and swabs transported in liquid medium, because a precise volume can be picked up and deposited.

This controlled inoculum volume is itself an improvement: manual inoculation deposits a variable amount, while the instrument delivers a consistent, calibrated volume, which matters for any test where the amount plated affects the result (such as a urine colony count).

Streaking is spreading that inoculum across the plate so that, by the final strokes, single organisms are separated far enough apart to grow into isolated colonies. This is the same goal as the manual streak-plate method; the difference is how the spreading is done.

The full principle of streaking for isolation, and the manual technique, is covered on the streak plate method page; this section is about how the instrument does it.

How automated streaking works: beads versus a loop

Automated processors streak in one of a few ways, and the streaking mechanism is the feature that most distinguishes the systems.

Magnetic-bead streaking is used by some systems (for example, BD Kiestra). A sterile magnetic bead is rolled across the plate along a controlled path, spreading the inoculum.

The manufacturer reports that rolling-bead streaking produces more isolated colonies than a manual loop and reduces the need for subculture, because the bead can cover the plate in a pattern a hand cannot easily reproduce.

Loop-based automated streaking is used by other systems (for example, WASP), where a mechanical arm streaks with a loop or applicator following a programmed pattern. It reproduces the logic of manual streaking, dilute the inoculum progressively across the plate, but does so identically every time.

In both cases the point is the same: the pattern is programmed and reproducible, so the isolation no longer depends on the individual technologist's technique. The instrument can also switch streaking patterns for different specimen and plate types automatically.

Why consistent streaking matters

Uniform streaking is not a cosmetic improvement; it changes the quality of what comes off the bench.

More reliable colony isolation means more plates yield well-separated colonies that can be picked directly for identification and susceptibility testing, with less need for subculture (which costs a day). Consistent inoculum volume makes quantitative results, such as urine colony counts, more reproducible.

And removing the manual streaking step frees technologists from a high-volume, low-skill task so their time goes to reading plates and working up cultures, the same "automate the repetitive, keep the judgment" pattern that runs through all laboratory automation.

Where the instrument fits: standalone and as a TLA front end

An automated specimen processor can be used on its own, as a standalone instrument that plants and streaks, after which plates are incubated and read manually. Used this way, it automates the single busiest manual step in the laboratory.

It is also the front end of a fully integrated line. In Total Laboratory Automation, the processor plants and streaks the specimen, then a conveyor carries the plate directly to a connected incubator and imaging system without anyone handling it.

The processor is the same instrument; in an integrated system it is simply connected to everything downstream. For how the connected systems work end to end, see Total Laboratory Automation in clinical microbiology.

Limitations

Automated processors handle liquid specimens best; swabs need to be collected into a liquid transport medium to be processed efficiently, and specimens needing special handling (tissue, biopsies) do not fit an automated line.

The instruments are a significant capital cost, justified by high, steady specimen volume rather than by a small workload.

As with any central instrument, a failure disrupts the workflow, so a manual streaking fallback and staff who retain the manual skill are still needed. And planting and streaking are only the front steps; the instrument does not identify organisms or read plates.

How to remember

• Plant then streak, both automated, one instrument. The processor deposits a measured inoculum, then spreads it in a programmed pattern. Two jobs, one machine.
• The win is consistency, not novelty. It streaks every plate the same way, so isolation no longer depends on whose hands are on the loop. Consistent isolation means fewer subcultures and cleaner colonies to pick.
• Bead or loop, same goal. Some systems roll a magnetic bead, others move a loop; both follow a programmed path to dilute the inoculum across the plate for isolation.
• Standalone or front end. Alone, it automates the busiest manual step. Connected, it is the entry point of a Total Laboratory Automation line.

Key exam facts

Fact	Detail
What it does	Automates planting (inoculation) and streaking of specimens onto culture plates
Best-known example	WASP (Walk-Away Specimen Processor); the front end of integrated systems
Planting benefit	Delivers a consistent, calibrated inoculum volume (matters for quantitative counts)
Streaking methods	Magnetic-bead streaking (e.g. Kiestra) or programmed loop streaking (e.g. WASP)
Main benefit	Reproducible streaking, better colony isolation, less subculture, frees staff
Best specimen type	Liquid specimens (urine, swabs in liquid transport medium)
Poor fit	Tissue, biopsies, specimens needing special handling
Relation to manual method	Automates the streak-plate technique; isolation principle is the same
Relation to TLA	Is the front end of a Total Laboratory Automation line
Key limitation	High capital cost; justified at high, steady specimen volume

Where students get confused

"Automated streaking is a different technique from manual streaking." The goal and the principle are the same, progressively dilute the inoculum across the plate so single organisms grow into isolated colonies. The difference is that the instrument does it along a programmed, reproducible path instead of by hand. The streak-plate logic is unchanged.

"The instrument identifies the organism too." No. An automated specimen processor plants and streaks. Identification and susceptibility testing are separate steps done by other instruments (MALDI-TOF, automated ID/AST) further along the workflow.

"A WASP and Total Laboratory Automation are the same thing." The processor is one instrument that plants and streaks. TLA is the whole connected line, of which the processor is the front end. A lab can have the processor alone, without full automation.

"Bead streaking and loop streaking give different results." Both aim for the same isolated-colony result; they are two mechanisms for spreading the inoculum reproducibly. The choice is a system-design difference, not a difference in what streaking is trying to achieve.

"Automated processing works for any specimen." It works best for liquid specimens. Swabs need liquid transport medium, and tissue or biopsy specimens still need manual handling. Automation extends to the specimens that suit a liquid-handling instrument.

References

1. Croxatto A, Prod'hom G, Faverjon F, Rochais Y, Greub G. Laboratory automation in clinical bacteriology: what system to choose? Clin Microbiol Infect. 2016;22(3):217-235. doi:10.1016/j.cmi.2015.09.030
2. Croxatto A, Dijkstra K, Prod'hom G, Greub G. Comparison of inoculation with the InoqulA and WASP automated systems with manual inoculation. J Clin Microbiol. 2015;53(7):2298-2307. doi:10.1128/JCM.03076-14
3. Bailey & Scott's Diagnostic Microbiology. Tille PM. 15th ed. St. Louis: Elsevier; 2022.
4. Leber AL, editor. Clinical Microbiology Procedures Handbook. 4th ed. Washington, DC: ASM Press; 2016. doi:10.1128/9781683670438.CMPH