Automated Microbiology Streaking: Navigating Anaerobic Bacteria

Written by Ross Garrison on October 8, 2025. Posted in Medical Microbiology.

Automated Microbiology Streaking

Navigating Anaerobic Bacteria Plating with Copan WASP and BD Kiestra

In today’s fast-paced clinical microbiology labs, automation is a game-changer for handling high volumes of specimens. Picture this: a busy shift where urine cultures, swabs, and blood samples pile up, and you’re relying on systems to streak plates consistently without the variability of manual work. Platforms like the Copan WASP and BD Kiestra have stepped up to make this possible, especially for anaerobic bacteria that demand careful oxygen control. But as helpful as these automated streakers are, they introduce challenges—particularly when it comes to media integrity during plating. Processes that expose plates to air can lead to oxidation, compromising results. That’s where specialized media, like Oxyrase’s OxyPRAS Plus plates, shine by resisting those pitfalls.

In this post, we’ll break down the systems, explore media options with their trade-offs, and see how enzymatic PRAS can make automation more reliable for anaerobes.

Understanding Automated Streakers in Anaerobic Plating

Overview of Copan WASP and BD Kiestra Systems

The Copan WASP, or Walk Away Specimen Processor, is a modular workhorse designed for liquid-based bacteriology. It automates everything from planting specimens to streaking with loops, prepping slides, and inoculating broths—handling up to 180 plates per hour. For anaerobes, it works well with tools like ESwab tubes, which preserve viability for short periods, but it falls short in any processing past the inoculation of the plate with the sample.

On the other hand, the BD Kiestra system, including its InoqulA module, uses rolling bead technology for precise, reproducible streaking. It’s part of a total lab automation setup that covers inoculation, incubation, imaging, and even result interpretation, with a media sorter holding up to 48 types. This standardization is a big win in clinical settings, reducing tech-to-tech variability. However, like the WASP, it can require manual tweaks for anaerobes, as automated handling will not immediately shuttle plates into oxygen-free environments.

Both systems boost efficiency and throughput, but their workflows—where plates might sit during sorting or streaking—can inadvertently expose media to ambient conditions, raising the risk of oxidation for oxygen-sensitive anaerobes like Clostridium or Fusobacterium.

Types of Media for Anaerobic Bacteria: Categories, Pros, and Cons

When plating anaerobes, the media’s reduction status is crucial because even brief oxygen exposure can hinder growth. Let’s look at the main categories, weighing their strengths and weaknesses in automated contexts.

Non-reduced media are basic and inexpensive. They’re easy to prepare and store, but they’re a poor fit for anaerobes—the high oxygen content outright inhibits strict species, leading to false negatives or poor colony development. In automation, where plates might linger exposed, these are rarely viable.
Post-reduced media start as standard but get reduced in anaerobic incubators after preparation. The upside is flexibility—you can reduce them on-demand—but consistency is an issue. The process is time-intensive, and any re-exposure to air quickly undoes the reduction, making them risky in high-throughput automated streakers.
Pre-reduced media are treated to low oxygen levels before use, offering better support for anaerobe growth right out of the gate. They’re more reliable than non- or post-reduced options, with decent storage under controlled conditions. However, their stability is limited; they can oxidize if not handled swiftly, which is a common snag in automated delays.
Traditional PRAS (Pre-Reduced Anaerobically Sterilized) media take it further by being both reduced and sterilized in an anaerobic environment. This ensures high reliability for culturing fastidious anaerobes, with good growth support. The cons? They’re pricier, have a shorter shelf life due to sensitivity, and can oxidize rapidly upon opening—within minutes in some cases—making them vulnerable in automated workflows.

Enter enzymatic PRAS, like Oxyrase’s OxyPRAS, which builds on traditional PRAS by incorporating an enzyme system to actively scavenge oxygen. This makes it the standout choice: it combines the reliability of PRAS with enhanced resistance to ambient air, allowing plates to withstand exposure without losing efficacy for up to 2 hours. Unlike the others, it doesn’t just passively maintain reduction—it fights oxidation dynamically, leading to better recovery rates and fewer workflow interruptions.

Learn more about enzymatic PRAS here.

Potential Detriments of Automated Processes to Media

How Automated Workflows Can Lead to Oxidation

Automated systems like WASP and Kiestra excel at streamlining lab processes, but the nature of their workflows can sometimes result in extended exposure to ambient air. For instance, during sorting, queuing, or transfer steps, plates may remain open longer than in manual handling. This allows oxygen to ingress, oxidizing the media and reducing its ability to support anaerobic growth.

The concern is particularly relevant for non-enzymatic media, where the reduction state can degrade quickly—studies indicate that standard plates might lose their anaerobic properties in just a few minutes under such conditions, turning an otherwise efficient process into one with potential reliability issues.

See how oxidation of media affects anaerobe recovery in our in house study.

Consequences in Clinical Settings

In practice, oxidation hits hard. It can yield smaller colonies or fail to isolate strict anaerobes altogether, forcing retests and delaying diagnoses. For example, in high-volume labs, this could mean higher error rates and wasted resources. Research highlights how non-PRAS options fare poorly in automated setups, with reduced isolation success for pathogens like Bacteroides—ultimately affecting patient care in scenarios like abscess or bloodstream infections.

The Role of Oxyrase’s OxyPRAS Plus Plates in Overcoming Challenges

Features of OxyPRAS Plus and the Oxyrase Enzyme System

OxyPRAS Plus plates are a prime example of enzymatic PRAS in action. They’re pre-reduced and anaerobically sterilized, but the real magic is the Oxyrase Enzyme System—membrane fragments that enzymatically remove oxygen. This allows the plates to resist oxidation for up to two hours in open air, far outpacing traditional media.They’re packaged in standard petri dishes, making them plug-and-play with systems like WASP and Kiestra—no special adaptations needed.

Advantages for Automated Applications

In automated workflows, OxyPRAS Plus tackles oxidation head-on by maintaining anaerobic conditions even during those inevitable delays in sorting or transfer. This leads to tangible wins: colonies can grow up to twice as large, recovery rates improve for tricky anaerobes, and the plates boast a 3-4 month shelf life for better inventory management.

From a lab perspective, this means fewer re-runs, lower costs, and smoother integration with automation. No more worrying about immediate incubation; the enzyme system buys you time without compromising quality. It’s particularly ideal for busy clinical environments where efficiency can’t come at the expense of accuracy.

Key Takeway

Automation with tools like Copan WASP and BD Kiestra is revolutionizing anaerobic plating in clinical microbiology, offering speed and standardization that manual methods can’t match. Yet, the risk of oxidation from workflow exposures underscores the need for smart choices in media categories like non-reduced, post-reduced, pre-reduced, and traditional PRAS, each with their own pros and cons. Enzymatic PRAS, exemplified by Oxyrase’s OxyPRAS Plus, emerges as the top option, providing robust resistance and better outcomes in automated settings.

If you’re optimizing your lab’s workflow, consider trialing these specialized plates. They could be the key to unlocking automation’s full potential while ensuring reliable results for your anaerobic cultures.

What is PRAS and Why Should Microbiologists Care About It?

Written by Ross Garrison on September 25, 2025. Posted in Medical Microbiology, Uncategorized.

Culturing Anaerobes in the Medical Laboratory

When you hear the term “anaerobe,” what comes to mind?

Hard to handle
Impossible to grow
Specialized equipment
Costly workflow
… Headache!

Anaerobes are a special case in bacteriology. Compared to aerobes and facultatives, which are generally straightforward to cultivate, anaerobes demand stricter conditions. They require additional equipment and more complex methods.

This raises the big question: how can we reduce complexity while maintaining the strict requirements needed for successful anaerobic growth?

To answer, we need to look at what makes anaerobic culture uniquely challenging.

Oxygen Toxicity: The Central Problem

Anaerobic bacteria vary widely in their sensitivity to oxygen. Some species, like Bacteroides fragilis, tolerate exposure thanks to enzymes that neutralize reactive oxygen species. Others, such as Porphyromonas levii, are extremely sensitive and quickly lose viability when exposed.

The challenge in the medical laboratory is that most specimens arrive with unknown bacterial compositions. We don’t know whether anaerobes are present, and if they are, we don’t know their tolerance level.

That leaves only one safe approach: treat every specimen as though it contains highly oxygen-sensitive anaerobes. Failing to do so means risking loss of clinically significant organisms.

Strategies to Protect Anaerobe Recovery

Step 1: Strict Control at Specimen Collection

Minimizing oxygen exposure starts at the bedside. If specimens are mishandled or stored improperly, the chance of recovering anaerobes drops dramatically.

Transport matters. Specimens should be placed in transport systems designed to support anaerobic survival.
Avoid oxidative environments. Even brief exposure can irreversibly damage oxygen-sensitive bacteria, leaving them unculturable by the time they reach the lab.

Step 2: Reduce Oxygen Exposure During Workup

Once specimens arrive in the lab, exposure to oxygen is unavoidable—unless you’re working in a full anaerobic chamber. The best strategy is to reduce the amount of time specimens spend in contact with oxygen.

Two practical steps:

Work in smaller batches.
Using jars or bags with large plate capacity creates delays. Early samples wait while the container fills, increasing their exposure time and allowing the media itself to oxidize. Working in small batches ensures plates are sealed into anaerobic conditions immediately after inoculation.

An even more streamlined option is OxyPlates, which generate their own anaerobic environment at the plate level. This eliminates the need for batching altogether and protects each sample as soon as it is processed.

Click here to learn more about OxyPlates.
Use media designed specifically for anaerobes.
Media must not only be oxygen-free but also chemically reduced. Here’s why that matters.

Step 3: Understand the Role of a Reduced Environment

Many labs use post-reduction—holding plates in an anaerobic chamber for 8–24 hours before inoculation—to create a reduced environment. While common, this approach has a critical weakness: it doesn’t remove oxidative byproducts formed during sterilization.

Standard anaerobic media often contain reducing agents, but when sterilized in the presence of oxygen, these agents react and form irreversible oxidative compounds. Even after post-reduction, the media environment is compromised.

The solution: Pre-Reduced Anaerobically Sterilized (PRAS) media.

What Is PRAS Media?

PRAS media is manufactured, sterilized, dispensed, and packaged under oxygen-free conditions. This process:

Prevents formation of oxidative byproducts.
Preserves the reducing agents in the media.
Provides plates that are ready for immediate use, no pre-reduction required.

For microbiologists, this means more reliable recovery of highly oxygen-sensitive species and less wasted time holding plates before inoculation.

Click here to learn more about PRAS.

Conclusion

Anaerobes are demanding, but successful recovery is possible when laboratories control three key factors:

Specimen collection and transport.
Minimizing oxygen exposure during processing.
Using media that arrives truly reduced, like PRAS.

By implementing these practices, labs can reduce complexity, improve recovery rates, and make anaerobic bacteriology more dependable.