Water, being a vital resource, demands the utmost attention to its safety and quality. The assessment of harmful microorganisms in water sources relies heavily on microbiological testing. In this blog, we will delve into the world of advanced methods for microbiological testing of water.

We will shed light on the techniques employed and highlight the essential microbiology products that are used in each method.

A. Membrane Filtration Technique:

The membrane filtration technique is a widely adopted method for detecting and enumerating microorganisms in water samples. It involves passing a known volume of water through a membrane filter with a pore size of 0.45 microns. The retained microorganisms on the filter are then transferred onto a solid culture medium for growth and enumeration.

TM Media's Membrane Filtration Technique solutions are renowned for their high-quality materials and consistent performance. We offer the following products specifically designed for this technique:

1. 1. Membrane Filtration Funnel with CN Gridded Membrane:

• Funnel capacity: 100 ml
• Membrane pore size: 0.45 microns
• Membrane diameter: 47 mm
• The grid printed on the membrane assists with colony counting after incubation.

2. M-Endo Agar, LES for detection of total coliforms:

• TM 174 M-Endo Agar, LES
• TM 175 M-Endo Broth
• TMV 174 M-Endo Agar, LES (Veg.)
• TM 773 M-Endo Broth MF (MF Endo Medium) (M-Coliform Broth)

This growth medium contains lactose and a pH indicator that changes colour in the presence of acid produced from lactose fermentation. Total coliforms typically exhibit a metallic (golden) sheen due to the production of aldehydes and acids from lactose fermentation. Some atypical total coliform colonies may appear dark red, mucoid, or have a dark centre without a metallic sheen. E. coli colonies exhibit a distinctive metallic sheen. Incubation of filters used for total coliform detection should be carried out at 35°C for 22–24 hours.

3. M-FC AGAR BASE for detection of faecal coliforms:

• TM 178 M-FC Agar Base
• TMV 178 M-FC Agar Base (Veg.)
• TM 179 M-FC Agar Base Modified
• TS 048 Rosolic Acid

This growth medium contains bile salts and rosolic acid, which inhibit the growth of bacteria other than faecal coliforms. It also includes aniline blue, a pH indicator that turns dark blue upon acid production, aiding in the identification of lactose-fermenting bacteria. Faecal coliforms appear as blue colonies on this medium, while E. coli colonies appear as flat, dark blue. Incubation of filters used for faecal coliform detection should be carried out at 44.5°C for 22–26 hours.

B. Multiple-Tube Fermentation Technique:

The multiple-tube fermentation technique, also known as the Most Probable Number (MPN) method, is employed for the enumeration of coliform bacteria in water. This method involves inoculating multiple tubes containing selective culture media with diluted water samples.

TM Media's Durham Tubes and Culture Media are formulated with specific nutrients and indicators. They enable accurate and reliable detection of coliform bacteria by observing gas production and colour changes.

Presumptive Stage:

During the presumptive stage, Lauryl Tryptose Broth (TM 150) primary fermentation tubes are inoculated with graduated quantities of the water sample. The tubes are then incubated, and the formation of gas within a specified time indicates a positive presumptive test.

Confirmed Stage:

The confirmed stage is performed on primary fermentation tubes that exhibit gas formation in the presumptive test. Brilliant Green Lactose Bile Broth (TM 365) tubes are inoculated with medium from positive tubes, and gas formation is observed after incubation.

Completed Test:

The completed test is carried out on samples showing positive results in the confirmed test. It involves streaking Eosin Methylene Blue Plates (TMP 025) with the sample, followed by incubation. Typical colonies are then transferred to Lauryl Tryptose Broth fermentation tubes and Nutrient Agar slants. Gas production in the fermentation tube and the presence of gram-negative, non-spore-forming, rod-shaped bacteria in the agar culture indicate a satisfactorily completed test.

C. Presence/Absence (P/A) Test:

The Presence/Absence (P/A) test is a qualitative method used to detect microbial contamination in water. It involves inoculating a selective broth medium with a water sample and observing for turbidity or growth after incubation.

TM Media's PA Broth (TM 571), enriched with nutrients and selective agents, facilitates the detection of various microorganisms, ensuring reliable test results.

In addition to the aforementioned techniques and products, TM Media provides a wide array of culture media specifically designed for water testing. These products further enhance the accuracy and efficiency of microbiological tests. Some of the notable Culture Media offered by TM Media include:

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• TM 498 Chloramphenicol Yeast Glucose Agar: This agar is utilized for the selective isolation and enumeration of yeasts and moulds in water samples.
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• TM 1251 Lactose TTC Agar (With Sodium Heptadecyl Sulphate): This agar, compliant with ISO 9308-1:2000 standards, is used for the detection and enumeration of Escherichia coli and coliform bacteria in water samples.
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• TM 440 Tergitol-7 Agar Base: This agar, following the specifications of IS: 5887 (Part I) 1976, reaffirmed in 2005, is employed for the detection and enumeration of heterotrophic bacteria in water samples.
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• TM 121 Hektoen Enteric Agar: This agar, in accordance with ISO 21567:2004, is suitable for the selective isolation and differentiation of Salmonella and Shigella species in water samples.
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• TM 492 XLD Agar: Xylose Lysine Deoxycholate (XLD) Agar is a selective medium used for the isolation, differentiation, and identification of Salmonella and Shigella species in water samples.
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• TM 036 Bile Esculin Agar: This agar, complying with ISO 10273:1994, is utilized for the enumeration and identification of enterococci in water samples.
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• TM 529 MacConkey Broth W/ BCP & NaCl: MacConkey Broth with BCP (Bromocresol Purple) and NaCl is employed for the detection and confirmation of coliforms in water samples, following ISO 9308-2:1990.
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• TM 666 Asparagine Proline Broth: This broth is used for the enrichment and detection of various microorganisms, particularly Pseudomonas aeruginosa, in water samples.
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• TM 899 Tryptophan Medium: Tryptophan Medium is utilized for the detection and confirmation of indole-positive bacteria in water samples.
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• TM 348 Simmons Citrate Agar: This agar is employed for the differentiation and identification of microorganisms based on their ability to utilize citrate as a sole carbon source.
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• TM 294 Selenite Cystine Broth (Fluid Selenite Cystine Broth): Following ISO 6579:1993 standards, this broth is used for the enrichment and selective isolation of Salmonella species in water samples.
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• TM 271 Reinforced Clostridial Broth: Reinforced Clostridial Broth is employed for the selective enrichment and enumeration of Clostridium perfringens in water samples.
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• TM 379 MacConkey Agar (W/ 0.15% Bile Salts, CV & NaCl): MacConkey Agar with bile salts, crystal violet, and NaCl is a selective and differential medium used for the isolation and differentiation of lactose-fermenting and non-lactose-fermenting gram-negative bacteria in water samples.
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• TM 217 Milk Agar (Brown and Scott, Modified): This agar is used for the detection and enumeration of bacteria capable of hydrolyzing casein in water samples, following the specifications of Part I and Part II.
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• TM 345 Soya Casein Digest Agar (Tryptone Soya Agar) (Caso Agar): This agar, complying with USP standards, is a general-purpose medium suitable for the cultivation and enumeration of microorganisms in water samples.
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• TM 1038 Nutrient Agar (pH 6.8): Nutrient Agar is a general-purpose medium used for the cultivation, isolation, and enumeration of microorganisms in water samples.
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• TM 358 Baird Parker Agar Base: This agar, when supplemented with Baird-Parker Selective Supplement, is employed for the isolation and enumeration of Staphylococcus aureus in water samples.
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• TM 2299 R2A Agar, modified: Modified R2A Agar is utilized for the cultivation and enumeration of heterotrophic bacteria from treated and untreated waters.
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• TM 371 EMB Agar, Levine: This agar, following ISO 21150:2015 standards, is used for the selective isolation and differentiation of Escherichia coli and other coliform bacteria in water samples.

Conclusion:

Microbiological testing plays a vital role in safeguarding public health and ensuring the quality of the water supply. By employing advanced techniques and utilizing reliable microbiology products, industries can ensure the safety and purity of water resources, leading to a healthier future for all. At TM Media, we offer a comprehensive range of high-quality microbiology products designed to meet the stringent requirements of water microbiological testing.

In the realm of food safety, the accurate and efficient detection of pathogens is crucial to ensuring the quality and safety of food products. Among the numerous pathogens that can contaminate food, Salmonella poses a significant risk to human health. A microbiologist should be well aware of the critical need for reliable methods to detect and identify Salmonella in food samples. In this blog, we will explore techniques and TM Media products designed to aid in the detection and identification of Salmonella, ultimately enhancing food safety protocols.

The Burden of Salmonella:

Salmonella is responsible for approximately 1.35 million illnesses, 26,500 hospitalizations, and 420 fatalities in the United States each year. It is imperative to have robust detection methods in place to minimize the risk of Salmonella contamination and protect public health.

Traditional Culture Method:

For decades, traditional culture methods, such as selective enrichment and plating techniques, have been the cornerstone of Salmonella detection. We understand the importance of these methods and offer a range of specialized Culture Media designed specifically for the isolation and identification of Salmonella. These Culture Media are available in both powder and prepared forms, providing convenience and flexibility in the laboratory.

Salmonella Detection Steps:

In accordance with ISO-6579-1-2017 guidelines, the following steps are commonly followed for Salmonella detection in various food samples:

Pre-enrichment in a non-Selective Liquid Medium:

The first step involves the inoculation of the test portion into Buffered Peptone Water (BPW), which is incubated at 37 °C ± 1 °C for 18 h ± 2 h. TM Media offers both Dehydrated Culture Media and Ready-to-Use Bags for Buffered Peptone Water, ensuring optimal growth conditions for Salmonella.

Buffered Peptone Water Ready-to-Use Bags offer a versatile pre-enrichment medium suitable for a wide range of samples and microorganisms. These bags comply with ISO 11133, ISO 6579, ISO 11290, ISO 21528, and ISO 6687 certifications, ensuring their safety and quality. They provide a convenient and time-saving solution, allowing for easy aseptic dispensing of the required media quantity through the needle port or spike port. The remaining media can be preserved in sterile conditions for future use thanks to the hanging resistance feature. With a generous shelf life of 12 months, these bags are not only cost-effective but also space-saving and energy-efficient.

Enrichment in Selective Semi-solid Medium:

Modified semi-solid Rappaport-Vassiliadis (MSRV) agar plates are utilized for enrichment. The culture obtained from pre-enrichment is inoculated onto MSRV agar plates, which are then incubated at 41.5 °C ± 1 °C for 24 h ± 3 h. TM Media provides Semisolid Rappaport Vassiliadis Medium, Modified (TM 1127), which facilitates the growth of Salmonella while inhibiting the growth of other bacteria.

Selective Plating and Identification:

From the enriched culture, selective solid media are employed for plating and identification purposes. TM Media offers a range of selective media suitable for Salmonella detection, including:

• SS Agar (TM 386): This medium selectively inhibits the growth of Gram-positive bacteria, allowing for the detection of Salmonella colonies that appear as colourless colonies with a black centre.
• Hektoen Enteric (HE) Medium (TM 121): HE Medium is both selective and differential, facilitating the isolation and differentiation of Salmonella colonies, which display characteristics such as blue-green colonies with or without black centres.
• XLD Agar (Xylose Lysine Deoxycholate Agar) (TMH 112): XLD Agar is a selective medium that inhibits the growth of Gram-positive bacteria and promotes the growth of Salmonella. Salmonella colonies on XLD Agar display distinctive characteristics, including red colonies with a black centre.
• Desoxycholate-Citrate Agar Medium (TM 2051): Compliant with IP regulations, this medium aids in the isolation and differentiation of Salmonella colonies, which appear as colourless and opaque colonies with or without black centres.
• Bismuth Sulphite Agar (TSM 039): This selective medium suppresses the growth of Gram-positive bacteria and enables the identification of Salmonella colonies. Salmonella colonies on Bismuth Sulphite Agar appear as black colonies with a metallic sheen.
• Brilliant Green Agar Medium (TM 951): This medium is used for identification of Salmonellae other than Salmonella typhi from faeces, foods, and dairy products. Salmonella enteritidis colonies appear as pinkish-white colonies, while Salmonella typhi colonies appear as reddish-pink colonies.

Each of these selective media offered by TM Media is designed to provide optimal conditions for the growth and identification of Salmonella, streamlining the detection process in food samples.

During Salmonella detection, it is essential to observe and interpret the colony characteristics on the selective media. This allows microbiologists to accurately identify potential Salmonella colonies.

Conclusion:

Ensuring food safety is of paramount importance in the food industry. The detection and identification of Salmonella in food samples play a vital role in minimizing the risk of contamination and protecting public health. With TM Media's advanced Culture Media and adherence to ISO guidelines, microbiologists in the food industry can enhance their food safety protocols.

TM Media offers a comprehensive range of Culture Media, including Buffered Peptone Water, Semisolid Rapaport Vassiliadis Medium, Modified, and selective media like Brilliant Green Agar, Desoxycholate-Citrate Agar, SS Agar, Hektoen Enteric (HE) Medium, XLD Agar, and Bismuth Sulphite Agar. These media are tailored to provide optimal conditions for the detection and identification of Salmonella colonies, enabling accurate and efficient screening.

Remember, accurate detection today means safer food tomorrow!

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