Water Microbiology

Water Microbiology: best kits and media. Consuming water, bottled water, bath water, natural waters… require large sample volumes (generally 100 or 250 mL) in the search for pathogens and their indicators.

MF

The most widely used method for working with such samples is Membrane Filtration (MF). In this method, these volumes are filtered and the filter is applied to the culture medium plate, so that colonies grow if the microorganisms sought are present.

https://www.microkit.es/eng/fichas/plaquis%20hermetic%20EN.pdf

MPN  Water Microbiology: best kits and media

Another very universal method is the Most Probable Number (MPN), in which several tubes or wells of liquid culture medium are used to extrapolate the count of the microorganisms sought, according to the number of positive tubes or wells (which change color). 

P/A Water Microbiology: best kits and media

And the third most widely used method is the Presence/Absence (P/A) method in which the microorganisms are not enumerated and the search is made to see if they are present or not in the sample by changing or not the color of the water. Since in all cases, we are looking for 0 to declare the water as suitable or >1 to declare it as unsuitable, obtaining a count can therefore be considered redundant.

MICROKIT offers you the Water Microbiology: best kits and media.

POUR PLATE

The only parameter for which only 1 ml of water sample is often analyzed is the aerobic count.

MICROKIT offers everything you need in water analysis, whatever method you use, and for all microbiological parameters. And using, as we use, the three methods, which is our favorite? We will see it throughout the text. Let’s look at the methods and their solutions one by one:

 

Total Plate Count in 1 mL of water sample (Water Microbiology)

Normally, 1 mL of water sample is added to a Petri dish, and after melting and cooling the solid medium to 45-47ºC, 15-25 mL of agar are added (sowing by mass inclusion).

The most commonly used media are YEA-Nutrient Agar (PCA-water) in water for human consumption (ISO 6222) and R2A in Pharmacopeial water.

Many laboratories use food microbiology variants such as PCA (although it is not suitable for the water oligotrophs such as YEA and R2A) or the general medium they have on hand, such as TSA.

Many laboratories use our chromogenic YEA (because the colonies grow much more clearly red in contrast to the cream medium). They even use it in the most convenient version that exists (DryPlates-TC Water), because it does not require melting and cooling media for the 1 mL of water to be sown in mass. And so the analysis time is reduced from 1 h to 10 seconds.

https://www.microkit.es/eng/fichas/Dry%20Plates%202021%20EN.pdf

In cooling waters, whether natural or contaminated ones, dipslides such as our Desinfectest-TC can be used, since they provide an estimate of the aerobic load (10E3, 10E4, 10E5…) without having to make dilutions.

https://www.microkit.es/eng/fichas/desinfectest%20EN.pdf

The rest of parameters usually requires samples of 100-250 mL:

 

MF Method for Water Microbiology

Coliforms/E. coli

For Coliforms/E. coli, the CCA chromogenic medium is used, which we at MICROKIT christened MugPlus in 1995. This is a great advance over the previous official medium (Tergitol TTC), especially in acidic waters. The blue colonies are of E. coli and the pink ones of the other coliforms. The blue ones can be confirmed immediately with Kovacs indole (+) on the same plate in the MICROKIT medium and the pink ones with oxidase reagent (-) also on the same plate.

https://www.microkit.es/eng/fichas/mugplus%20EN.pdf

faecal Enterococci

For faecal Enterococci, Slanetz-Bartley Agar (SB, red colonies) is used followed by Bile Esculin Azide Agar (BEA, white colonies with a black halo). At MICROKIT we have validated our Rapid-BEA so that the filter can be used directly on this medium, avoiding the previous step through SB, which allows us to give results in 18 hours instead of the usual 48 hours. And for those who prefer chromogenic media, our EPA medium has the same performance, with dark blue colonies.

Clostridium perfringens

For Clostridium perfringens and its spores, TSC Agar (black colonies) and Acid Phosphatase are used to confirm them (preferably in its fluorescent MUP version, because it is not carcinogenic). At MICROKIT we also offer the chromogenic medium (orange colonies unlike TSC, which do not revert after removing the plate from the anaerobic atmosphere). Despite being a parameter of maximum importance (the two previous ones indicate contamination by waste water, but this one indicates contamination by natural waters, often with protozoa such as Cryptosporidium), the intercomparative services show that the poor results (50% false negatives and a 1-3 log drop in the counts) are not due to the medium, but to the MF method, because it oxygenates the anaerobes in the water in a way that is lethal to them. At MIcrokit we have invented a magnificent solution with the same TSC medium that we will see later (Quanti-P/A).

Pseudomonas aeruginosa

For Pseudomonas aeruginosa (bottled water, bathing water, water for hospital consumption…), Cetrimide Agar CN is used (lobed colonies, often phosphorescent, yellow, green or blue). At MICROKIT we also have the chromogenic medium that gives results in just 18 hours instead of the 48 hours of the classic CN: alert in 18h by red colonies, confirmed with fluorescent halo in 48h. If no red colonies in 18h, no Pseudomonas aeruginosa are present.

coliphages

For bacteriophages (somatic coliphages) must be used Scholten Agar and search for and look for growth plaques of the E. coli strain inoculated on the plate. It is a new parameter of the latest renewal of EU legislation 1/2023 that is an excellent indicator of traveller’s diarrhoea, micro-epidemics… At MICROKIT we also offer the other 5 media required by ISO 10705 for these and the other bacteriophages mentioned therein.

https://www.microkit.es/eng/fichas/BACTERIOFAGOS%20SCHOLTEN%20AGAR.pdf

Water Microbiology

 

MPN Method

For Coliforms/E. coli, there is an ISO that talks about a medium with a defined substrate, but our Colicult is more recent and better because it also detects enterotoxigenic E. coli. Coliforms turn 100 mL of water blue and E. coli fluoresces blue in the dark. It can also be confirmed directly with Indol Kovacs in seconds. You can use the cuvettes from this ISO or also our own (NMP-Racks) with our own NMP tables.

For fecal Enterococci there is also an ISO with a fluorogenic medium, but our Enterocult broth (based on BEA) is newer and better. ISO cuvettes or our NMP-Racks can also be used.

For Clostridium perfringens and its spores, this NMP Method does not work well, because it requires an anaerobic atmosphere. That is why at MICROKIT we invented the Quanti-P/A bags with TSC, cold gelling agent and an anaerobic atmosphere. 100 mL of sample water are introduced, mixed with the medium by kneading, incubated, and the black colonies are observed and enumerated.

https://www.microkit.es/eng/fichas/QUANTI-PA%20Clostricult%20EN.pdf

For Pseudomonas aeruginosa you can use the USA fluorescence method with the aforementioned cuvettes. Or better yet, our Pseudocult, which in addition to fluorescence, turns pink in positive wells. Our cuvettes NMP-Racks can also be used.

Water Microbiology

 

P/A Method

Although for us it is the most logical method (why to be counting zeros?), easier to use and more reliable, some legislations have relegated it to work in laboratories not subject to ISO standards and to field work (for natural waters, wells, taps…), which is no small feat.

The same broths mentioned in the NMP method, are used to determine whether or not coliforms-E. coli, fecal Enterococci, Pseudomonas aeruginosa and many other parameters are present. No cuvettes are necessary. Simply add the 100 mL of water sample to the medium, incubate it and observe whether there is a color change (+) or not (-).

For Clostridium perfringens and its spores, Clostricult P/A is sufficient without the need to use Quanti-P/A TSC; this method also does not require anaerobic incubation. Black (sometimes only the bottom of the container): positive, otherwise: negative.

This method is so successful at MICROKIT that we have designed 3 formats, to choose from depending on the convenience, number of samples or budget of each client:
1-The classic sample bottle, with the sterile medium already hydrated, to add the 100 mL of water directly into it

https://www.microkit.es/eng/fichas/P-A%20kits%20in%20sampler%20bottles%20EN.pdf
2-The economical format for larger consumers: pre-weighed vials of sterile powder medium

https://www.microkit.es/eng/fichas/P-A%20powder%20vials%202021.pdf
3-The very economical format in 100 g jars of sterile powder medium: add a teaspoon to 100 mL of water sample and close the rest of the jar for later uses

https://www.microkit.es/eng/fichas/P-A%20Kits%20in%20100%20g%20bottles%20EN.pdf

Water Microbiology

We also offer kits that contain the P/A and DryPlates components necessary for the analysis of each type of water:

A) Water for human consumption

https://www.microkit.es/eng/fichas/drinking%20water%20kit%20EN.pdf

B) Bath water

https://www.microkit.es/eng/fichas/swimming%20pool%20kit.pdf

C) Water for cosmetic use

https://www.microkit.es/eng/fichas/COSMETIKIT%20WATER%20EN.pdf

 

Others

And we also have quantitative strains, confirmation kits, bottles and bags, membranes, and everything necessary for any laboratory, regardless of size, to be able to analyse its water samples in the way that best suits it.

https://www.microkit.es/eng/fichas/QUANTITATIVE%20MICROBIOLOGICAL%20STRAINS%202017.pdf

https://www.microkit.es/eng/fichas/m%20ident%20EN.pdf

https://www.microkit.es/eng/fichas/Exclusive%20MICROKIT%20products%20for%20water%20with%20their%20differential%20advantages.pdf

https://www.microkit.es/eng/fichas/MICROKIT%20export%202024%20Catalogue.pdf

 

Request more information and prices at export@microkit.es

If you want to order some MICROKIT product, please send your order to: pedidos@microkit.es