Microbiological Dipslides are simple bacteria detection tools in terms of their ease of use and how they work.

In the simplest terms, dipslides are sterile plastic paddles featuring growth media on both sides of the paddle. If bacteria is present in a sample that you dip a dipslide into, bacteria will grow on the growth media (agar) to form easy to view / count colonies.

That's pretty straightforward but why do micro-organisms grow on agar?

In order to survive and grow, bacteria, yeasts and moulds require nutrients, water and environmental conditions such as specific temperatures and oxygen (unless it is anaerobic bacteria).

The agar used on our dipslides is formulated to meet the needs of the micro-organisms so that they will grow and not be inhibited. The agar contains nutrients and water and the recommended incubation temperatures provide the correct environment for growth.

The dipslides that we offer are either general or selective dipslides.

If it is a general dipslide, this means that the agar generally meets the requirements of a wide range of micro-organisms and will give you a general, non selective microbial count.

If it is a selective dipslide, this means that the agar has been formulated to specifically meet the needs of one type of micro-organism. Selective agars also inibit the growth of other types of bacteria, yeasts or moulds. Additives such as antibiotics can be added to the formulation to aid in suppressing growth of other (non target) organisms.

Examples of general, non selective dipslides: General purpose dipslides (total bacteria count, yeasts and moulds).

Examples of our selective dipslides: E.coli, Pseudomonas, Urinary organisms.

Agar formulations

Agar formulations generally contain nutrients (carbon sources, nitrogen sources, vitamins), carbohydrates (energy source) and mineral salts. Sometimes indicator dyes or selective agents can also be included.

As an example of an agar forumulation, you can see our Nutrient TTC agar formulation (aside from water) below. This is a general agar that is non selective and is designed to grow a variety of micro organisms.

'Lab-Lemco' powder - (nutrients, non fermentable carbohyrates, minerals)

Yeast extract - (nutrients, carbohydrates, minerals)

Peptone - (nutrients)

Sodium chloride (salts / minerals)

Agar (gelling agent)

Gelatin (gelling agent)

Triphenly tetrazolium chloride (indicator dye) - bacteria reacts with this dye and colonies have a red appearance (this can be seen in our MCBTM2, Metal Working fluid Dipslides)

It also important that the pH of the formulation is ideal for microbiological growth.

If the microbe's needs aren't met

Lack of water: If the dipslide is stored outside of recommended temperatures and too much moisture / sterile water evaporates from the agar, it will become dried out. This would then no longer provide the water content that the bacteria needs to grow.

Lack of nutrients: Micro-organisms have a range of basic requirements that they need in order to grow. Some organisms have more complex needs and require supplements / extra nutrients. If the agar formulation does not meet the needs of the target organisms, they will not grow.

Temperatures outside of ideal range: Organisms grow best at a specific temperature range. This will differ depending on which bacteria, yeast or mould you are testing for. If the temperature is too low (e.g an incubator isn't used), the microbes won't grow.

Using dipslides

To use dipslides, they are either dipped into a sample, pressed against a surface or the sample is swabbed on to the dipslide using a sterile swab.

Dipslides are then placed into an incubator for incubation at the correct time and temperature for that particular dipslide.

Once incubated, results are compared with the chart provided so that the colony forming unit level can be calculated.

We hope that this blog post helps to explain how and why dipslides grow bacteria. If you have any further questions regarding this, please contact us.