Don't let Listeria shut you down - Puritan ESK

Rapid Culture Based Techniques

Rapid Culture Techniques for Manual Microbiology - the Next Generation

Key Points

  • Techniques that rely on organism growth and metabolism to produce a characteristic reaction
  • Novel media contains specific growth promoters, inhibitors and/or chromogens
  • Easy to validate, low cost per test

RapidMethodCulture Microbiology is on a cusp; on one side, for almost twenty years the word rapid has been applied to developments in methodology reliant upon growth-based, cultural techniques. On the other side, real-time polymerase chain reaction (RT-PCR) assays can now, in some situations, offer same day results and are potentially poised to turn the microbiology lab into the molecular diagnostics department.

However such techniques normally come at an 'added value' price that many labs either cannot afford or cannot justify, if for example there is no definable cost benefit to the organisation in real time results. These labs require tests that are low capital and lower consumable costs, easy to establish and validate, with low maintainance and minimal technician training required.

So there is still very definately a need for novel cultural technologies designed to take days off the standard time to result. Let’s examine what’s on offer for rapid manual cultural microbiology - this may be the last stop before PCRville but they still offer many advantages.


At a practical level, microbiology can be split between pathogen testing and those organisms that will cause product spoilage and/or stability issues.  It is also possible to draw a line between true cultural techniques and those using some metabolite to indicate that growth has occured normally by adapting the presentation of the media to include devices other than Petri dishes, and invariably using an instrument of some description, here we are just going to focus on novel cultural media.

As a general rule, with the exception of fungal tests, most quality indicator organisms can be reported within 48 hours utilizing traditional media inoculated direct from a homogonized sample. These media formulations have been relatively unchanged for at least the last twenty-five years with efficacy largely empirically derived.

In terms of time to result, the same cannot be said for pathogens. With the requirement for more sensitive detection limits, an enrichment stage, or stages, needs to be included followed by confirmatory tests. This not only extends the time to result, (and this can be up to seven days for Salmonella spp and Listeria spp), but also increases labor and consumable costs. With commercial pressures acting to reduce the reporting timeframe, traditional growth media formulations began to evolve.

Leading this change away from traditional, empirically derived selective and diagnostic features were the chromogenic and fluorogenic plating media. Such media allowed species specific diagnostic features to be designed into direct plating media that would previously have required sub-culture and further testing. An early example would be the inclusion of the fluorogenic substrate methylumbelliferone -β -D-glucoronide (MUG) into bile salt media for the specific diagnosis of E.coli amongst lactose fermenting, bile tolerant Gram negative flora.

Chromogenic substrates followed closely, allowing colour to report the presence of specific species amongst closely related accompanying flora. Early examples were designed to report extra-cellular enzymatic activity and as such the reactions were not colony associated and diffusion of the colour into the surrounding media occurred. As with all emerging technologies there were some early problems and the regulatory framework was slow to adopt the novel media. However the take-home message for microbiologists was clear; cultural techniques could now be used to reduce extended reporting timescales by making species specific diagnostics available on primary plating media.

The latest generation of chromogenic media take this even further. From an improved understanding of genotype and gene expression, specific intra-cellular enzyme systems are targeted with substrates that produce colony associated colour reactions. Also, combining enzyme/substrate systems within the same medium allows differential diagnosis to take place, e.g. UTI media that can report the presence of 2 or 3 target groups of organisms on one plate.

The very latest innovations in rapid cultural techniques reduce the time taken to enrich target pathogens in recovery systems designed to lead into chromogenic diagnostic media. With the inclusion of an inhibitor it is now possible to specifically reduce the growth rate of a competitor species within a recovery system. If the recovery system also contains specific growth promoters for the target species then a single broth (ONE broth Salmonella and ONE broth Listeria) can combine a resuscitation and growth stage together into one enrichment. This is a revolution for the food lab, cutting two steps down to one, reducing labor costs, and allowing earlier inoculation onto specifically designed chromogenic plating media.

Such systems designed for Salmonella spp and Listeria spp allow diagnostic recovery within 48 hours as opposed to a more typical 5 day test.  These cultural techniques have addressed the commercial pressures to report earlier on the microbiological status of valuable inventory, without the need to invest in capital equipment. Regulatory acceptance of these novel approaches is well advanced with ISO standards now incorporating single broth enrichment followed by chromogenic plating.


Single broths can combine resuscitation and growth stages reducing labor and consumables

Chromogenic plating offers easy identification and differentiation reducing the number of presumptives

Start-up costs are significantly lower than instrumental techniques

Improved regulatory recognition makes them more accessible for SME organizations.


Related News:

COPAN Launches CYCLONE AUTO-PREP™ with Smart Incubators and AI at IAFP

Smart Incubators and AI for Food MicrobiologyThe CYCLONE AUTO-PREP™ fully automates the traditional pour plate method for TVCs on liquid samples, with optional Smart Incubators and the use of Artificial Intelligence (AI) for automatic colony counting and colony recognition.

Choose INTERSCIENCE for your Microbiological Analyses

Discover BAGSYSTEM from INTERSCIENCEINTERSCIENCE provides full equipment for safe analysis, from solid sample preparation to final bacterial enumeration and results - lab homogenizers, sterile filter bags, gravimetric dilutors, automatic platers, automatic colony counters and various lab tools.

Seward and Inlabtec Announce US Sales Cooperation

Seward and INLABTEC Food Microbiology Sample PrepSee how the new Stomacher 400 EVO and iNLABTEC Serial Dilution system can streamline your laboratory sample preparation and reduce single use plastics. Seward and iNLABTEC will be presenting together for the first time at IAFP 2018 Booth #324 .

Dry Sample-ready Plates Are Ideal Alternative to RMMs

Replace the Petri dishExperts in the food microbiology testing market, Strategic Consultants, Inc. report that around 50% of global microbiological testing is still done on traditional media. But that doesn't mean everyone is filling plates with agar.

Now Available: First Plant-based PCA from Döhler

Plate Count AgarDöhler’s first Plant-Based, Plate Count Agar (PCA) is a standardised and ready-to-use culture medium for the rapid and reliable quantitative detection of total viable microorganism count.

Choose test method guide:

Select by Organism:
Select by Test Method:
Solutions for dairy microbiology
Compare cost of Baker Bugbox with Gas Jars

© 2001 - 2018 Rapid Test Methods Ltd • Please join us on Twitter, Facebook and LinkedIn • RSS Feed