Food Microbiology: 6 Tips to Choose the Best Culture Media Preparator

When using enrichment broths in a food microbiology laboratory, there are several options:

• Ready-to-use media (in 3 or 5-liter bags)
  
• Semi-ready-to-use media (requiring the addition of sterile water)
  
• Producing sterile culture media with an autoclave
  
• Producing sterile culture media with a culture media preparator (also known as automated culture media preparation system).
  

According to our LinkedIn survey, 16% of SuperMicrobiologistes currently use media preparators in their laboratories.

This percentage would likely be much higher if the question had been asked exclusively to food microbiology laboratories.

In this article, we will take a closer look at media preparator to understand their advantages and disadvantages.

We will also share some tips to help you choose the most suitable media preparator for your microbiology laboratory.

Table of Contents: :

• How a media preparator works?
• Advantages
• Disadvantages
• How to choose the best media preparator?
• Conclusion

How a Culture Media Preparator Works

The culture media preparator are used in microbiology laboratories to produce sterile culture media.

This type of device can be used to prepare:

• Solid culture media, such as agar (in smaller tanks, typically less than 10 liters).
  
• Liquid culture media, such as enrichment broths (in larger tanks, typically over 10 liters).

The media preparator is equipped with a stainless steel tank where the powder (culture media) and water are added. Once started, the automatic media preparator mixes and sterilizes the solution according to a specific sterilization schedule with precise temperature and time settings.

Solid culture media, such as agar (in smaller tanks, typically less than 10 liters).

Once the sterilization cycle is complete, the media preparator can be connected to a peristaltic pump, a gravimetric diluter (for broths), or a dispensing system (for agar Petri dishes).

Today, most culture media preparator found in food microbiology laboratories are used to produce enrichment broths such as Buffered Peptone Water (BPW) or Fraser Broth (for Listeria detection).

“Freshly prepared culture media produced in the laboratory are the most effective.”

Source: This might be true, but we couldn’t find any scientific literature to back it up.

Advantages of a Media Preparator

It all depends on what you’re comparing it to… an autoclave or ready-to-use media (bags)? Let’s take a look:

Advantages of a Media Preparator Compared to Ready-to-Use Media Bags 

Cheaper: This, of course, depends on the laboratory’s volumes, but in many cases, the cost per liter of broth produced with a media preparator is lower than that of the same media in ready-to-use bags.

Less handling: Would you rather handle 20 bags of 3 liters each day or simply connect a hose between your gravimetric diluter and your 60-liter media preparator?

Handling multiple heavy bags can increase the risk of MSDs (Musculoskeletal Disorders), while using a media preparator significantly minimizes this risk.

Advantages of a Culture Media Preparator Compared to an Autoclave

Higher production capacity: With an autoclave, you’re limited by the size of the bottles. A media preparator allows you to produce the full volume of its tank, ranging from 2 to 100 liters.

Better media quality: During its cycle, the media preparator continuously homogenizes the media, ensuring uniform temperature during sterilization. This prevents overheating, which can destroy nutrients or caramelize sugars, issues that can occur with an autoclave.

Single weighing step: Using an autoclave requires weighing media powder for each bottle. With a media preparator, you only need to weigh the powder once for the entire batch.

Disadvantages of a Culture Media Preparator

While media preparators have many advantages, they also come with some drawbacks.

These are not deal-breakers but are important to understand before making the investment.

Disadvantages of a Media Preparator Compared to an Autoclave

Versatility: The main disadvantage of a media preparator compared to an autoclave is its limited versatility. A media preparator is designed exclusively to sterilize culture media, and only one type of media can be processed per sterilization cycle.

An autoclave, on the other hand, can sterilize multiple types of culture media in a single cycle. Additionally, it can be used to sterilize other items such as tubing, knives, pipette tips, and more.

It can also be used for waste decontamination.

Disadvantages of a Media Preparator Compared to Ready-to-Use Media Bags

Delay before use: You need to wait for the sterilization cycle to complete before using the enrichment broth. Depending on the volume and the preparator’s capacity, this can take up to 2 hours (including cleaning, preparation, heating, sterilization, and cooling). In contrast, a ready-to-use bag is usable in less than a minute.

Defining a batch: For ready-to-use bags, the batch is clearly defined. With a media preparator, it’s more complex.

If your lab is accredited, ISO 11133 requires testing the performance of each batch. But with a media preparator, what constitutes a batch? Is each sterilization cycle considered a batch?

We’ve dedicated an article to this topic: ISO 11133 and Media Preparators: How Food Microbiology Labs Manage the Concept of a Batch? (soon available)

If your lab is accredited, ISO 11133 requires testing the performance of each batch. But with a media preparator, what constitutes a batch? Is each sterilization cycle considered a batch?

Staff training: Personnel must be trained (and possibly certified) to clean, prepare, and operate the media preparator.

Risk of breakdown: Like any electronic device, a media preparator has a higher risk of failure compared to ready-to-use bags. This needs to be factored in. What’s the backup plan in case of a breakdown? Keeping ready-to-use bags on hand might be a good idea.

Investment: While the cost per liter is lower, the initial purchase price of a media preparator is significant (ranging from €20,000 to €100,000 depending on the model). Don’t forget to include annual maintenance costs in your budget.

If you’re now convinced that a media preparator is the right choice for your microbiology laboratory, let’s move on to the next step: Choosing the right model.

How to Choose the Best Media Preparator?

The best media preparator for one microbiology laboratory may not be the best for another. It all depends on your workflow and organization. However, here are several tangible criteria to consider when purchasing a new media preparator:

1 – Sterilization Cycle Duration

While the sterilization time itself cannot be changed, the heating and cooling speeds can make a significant difference.

These depend on the power of the heating elements and the efficiency of the agitation system.

The time saved can be considerable… especially when you’re in a hurry in the lab.

2 – Cleanability of the Tank

Is the tank and its agitator easy to clean?

The more corners, bends, and “dead zones” there are, the higher the risk of contamination.

Imagine the disaster if your batch of BPW (Buffered Peptone Water) gets contaminated, and you only realize it 24 hours after using 60 liters!

3 – Durability of the Media Preparator

This device is expected to be used daily (and even multiple times a day) for 8 to 10 years. It needs to be robust and reliable… and not all manufacturers meet this standard.

Ideally, seek feedback from other users to ensure you’re making the right choice.

4 – After-Sales Service

Sorry to be a buzzkill, but breakdowns are inevitable over the lifetime of a media preparator.

The real question is: how will your supplier’s after-sales service handle them?

Ask about their average response times, the availability of spare parts, and the MTBF (Mean Time Between Failure) for the specific preparator model you’re considering.

This information is crucial to avoid prolonged downtime.

5 – Energy Consumption

This is a relatively new consideration, but one that shouldn’t be overlooked.

Rising electricity costs can significantly impact the ROI (Return on Investment) of the device.

Be sure to compare the actual energy consumption of different models.

6 – Water Consumption

A media preparator uses water to cool the culture media at the end of the cycle, which can amount to tens of thousands of liters over a year.

The issue with water isn’t so much its cost (for now) but rather the sense of waste felt by lab teams watching such large amounts go down the drain. This can be especially frustrating for staff who are personally restricted from watering their gardens or washing their cars.

This perceived waste can negatively impact employees’ sense of purpose at work… a factor that’s critical to consider, especially when retaining skilled microbiologists is already a challenge.

Be sure to compare the water consumption of each device.

Conclusion

In summary, using an automatic media preparator offers undeniable advantages, such as reduced cost per liter, high production capacity, and consistent media quality.

However, drawbacks like limited versatility compared to an autoclave, delays before use, and the risk of breakdowns should not be overlooked.

When choosing a media preparator, it is crucial to consider criteria such as cycle duration, cleanability, durability, after-sales service, and electricity and water consumption.

By carefully evaluating these factors, each laboratory can select the option best suited to its food microbiology needs.