1. Historical Background and Development:

Fluid Thioglycollate Medium (FTM) emerged from early 20th-century research focused on cultivating anaerobic and fastidious microorganisms. Its development built upon studies of reducing media, which lowers the oxidation-reduction potential to support the growth of oxygen-sensitive bacteria. Sodium thioglycollate was incorporated as a key reducing agent, enabling the creation of microaerophilic and anaerobic conditions within the medium. The formulation was progressively refined with the addition of nutrients such as peptones, yeast extract, and dextrose to support a broad spectrum of microorganisms. While no single individual is credited with the discovery of FTM, its evolution represents cumulative advancements in microbiology, particularly in the cultivation of anaerobic bacteria and the standardization of sterility testing protocols, including those later formalized in USP <71> for pharmaceutical applications.

2. Principle of the Medium:

FTM functions on the principle of creating a reducing environment conducive to the growth of both aerobic and anaerobic microorganisms while simultaneously supporting fastidious organisms through its enriched nutrient composition. Key aspects include:

• Reduction of oxygen: Sodium thioglycollate binds free oxygen, lowering the redox potential of the medium. This allows anaerobic bacteria to thrive in the lower part of the medium while aerobic organisms grow near the surface.
• Indicator for oxygen diffusion: A small amount of resazurin is included as a redox indicator. It turns pink in the presence of oxygen and remains colorless under anaerobic conditions, providing a visual cue of oxygen distribution in the medium.
• Nutrient enrichment: Peptones, yeast extract, and dextrose provide carbon, nitrogen, vitamins, and growth factors necessary for the cultivation of a wide range of microorganisms.

Through these mechanisms, FTM allows simultaneous detection of obligate aerobes, obligate anaerobes, facultative anaerobes, and microaerophilic bacteria in a single medium.

3. Purpose and Rationale for Development:

The primary objective of Fluid Thioglycollate Medium (FTM) is to provide a versatile environment for the cultivation and detection of a wide range of microorganisms, including aerobic, anaerobic, and fastidious species.

In pharmaceutical and medical device sterility testing, FTM supports the growth of diverse microbial populations, ensuring that products labeled as sterile are free from viable contaminants.

For clinical microbiology, the medium enables the propagation of oxygen-sensitive pathogens, such as Clostridium spp., Bacteroides spp., and Listeria spp., which require reduced oxygen conditions for optimal growth.

In industrial and food microbiology, FTM is employed to detect microbial contamination in raw materials, processed foods, and beverages, particularly targeting organisms inhibited by standard aerobic media. By providing a reducing environment coupled with nutrient enrichment, FTM effectively addresses the challenges associated with cultivating microorganisms across varying oxygen requirements, ensuring reliable recovery and detection of both aerobic and anaerobic contaminants.

4. Composition of Fluid Thioglycollate Medium:

Fluid Thioglycollate Medium (FTM) is a nutrient-rich, reducing medium formulated to support the growth of aerobic, anaerobic, and fastidious microorganisms. Its composition includes pancreatic digest of casein (peptone) as a source of nitrogen and amino acids, yeast extract for vitamins and growth factors, and dextrose as a fermentable carbohydrate to provide energy. Sodium thioglycollate and L-cystine serve as reducing agents to lower the oxidation-reduction potential, creating an environment conducive to the growth of oxygen-sensitive organisms, while resazurin functions as a redox indicator, turning pink in the presence of oxygen and remaining colorless under anaerobic conditions. A small amount of agar stabilizes the oxygen gradient within the medium, and the pH is adjusted to 7.1 ± 0.2 at 25 °C to optimize microbial growth. The medium is sterilized by autoclaving and carefully cooled to preserve the oxygen gradient, which is essential for the selective cultivation and differentiation of aerobic, facultative, and obligate anaerobic microorganisms.

5. Applications in Microbiology:

5.1 Clinical Microbiology:

FTM is employed for the cultivation and detection of anaerobic and fastidious pathogens in clinical specimens, including blood, wound swabs, and tissue samples. Its reducing environment allows growth of oxygen-sensitive organisms that may not grow on standard aerobic media.

5.2 Pharmaceutical and Biologics Sterility Testing:

FTM is a regulatory-compliant medium for USP <71> sterility testing, supporting the recovery of aerobic and anaerobic contaminants in parenteral preparations, vaccines, and other sterile pharmaceutical products.

FTM plays a critical role in microbial limit testing (MLT) for the assessment of bioburden and the assurance of microbiological quality in pharmaceutical products, cosmetics, nutraceuticals, raw materials, and finished products.

5.3 Industrial and Food Microbiology:

In food and beverage microbiology, FTM is employed to detect spoilage microorganisms, especially anaerobic bacteria in products such as canned foods, dairy, and beverages. Its enriched nutrient composition supports the recovery of low-level or stressed contaminants, ensuring reliable detection of potentially harmful or spoilage-causing organisms.

6. HiMedia Fluid Thioglycollate Medium (LQ026, MU009, M009, MAP009, CM009, MV009):

HiMedia Laboratories Pvt. Ltd. provides Fluid Thioglycollate Medium (FTM) in both dehydrated and ready-to-use formulations, specifically optimized for sterility testing, microbial quality control, and research applications. HiMedia FTM is manufactured under stringent quality control protocols to ensure consistency, reliability, and regulatory compliance. The medium meets USP <71> standards, making it suitable for pharmaceutical sterility testing of parenteral preparations, medical devices, and other sterile products.

HiMedia FTM supports the growth of aerobic, anaerobic, and fastidious microorganisms, including oxygen-sensitive and metabolically stressed organisms, thereby enabling comprehensive microbial detection across diverse sample types. Each production batch is accompanied by batch-specific Certificates of Analysis (CoA) and detailed technical documentation, providing assurance of compliance with regulatory and quality requirements.

The medium demonstrates reproducible performance, with a clearly defined resazurin-based oxygen gradient that allows visual differentiation of aerobic and anaerobic zones, facilitating accurate interpretation of microbial growth. Its user-friendly design ensures ease of preparation, whether using dehydrated powder, granulated or ready-to-use formulation, and supports standardized laboratory protocols for sterility testing, microbial enumeration, and quality assurance in clinical, pharmaceutical, industrial, food, and environmental microbiology.

7. Interpretation of Results in HiMedia Fluid Thioglycollate Medium (LQ026V):

• Obligate aerobes: Grow near the surface where oxygen is present.
• Facultative anaerobes: Grow throughout the medium.
• Obligate anaerobes: Grow near the bottom of the medium, in the oxygen-depleted zone.
• Indicator (resazurin): Pink-Purple at the top indicates oxygen presence; colorless at the bottom indicates anaerobic conditions.
• Incubation: For general cultivation, incubate at 30–35 °C for 18–24 hours or longer, up to seven days, to facilitate the detection of slow-growing organisms. For sterility testing, incubate for up to 14 days in accordance with USP <71>.

8. Key features of HiMedia’s FTM:

• Broad-spectrum growth: FTM supports the growth of a wide range of microorganisms, including Clostridium sporogenes, Pseudomonas aeruginosa, and Staphylococcus aureus, ensuring comprehensive sterility and microbial limit testing.
• Ready-to-use and dehydrated formats: HiMedia offers FTM in convenient ready-to-use liquid formulations (LQ026) available in multiple volumes to meet customer requirements, as well as in dehydrated powder forms (M009, MU009, MAP009) and granulated form (GM009), providing flexibility across laboratory workflows.
• Sustainable options: HiVeg® peptone variants (MV009) are plant-based, animal component–free alternatives that are environmentally sustainable and deliver growth performance equivalent to or superior to conventional formulations.

9. Conclusion:

Fluid Thioglycollate Medium (FTM) is a critical tool in microbiology, offering a versatile and nutrient-rich environment for the cultivation of aerobic, anaerobic, and fastidious microorganisms. Its reducing agents, coupled with a resazurin-based redox indicator, create a controlled oxygen gradient that enables the detection and differentiation of microorganisms with varying oxygen requirements. FTM plays a pivotal role in clinical diagnostics, pharmaceutical sterility testing, food and beverage microbiology, and research applications, ensuring reliable recovery of low-level or oxygen-sensitive organisms. Commercial formulations such as HiMedia FTM provide standardized performance, reproducibility, and compliance with regulatory standards, reaffirming the medium’s enduring value in modern microbiological analysis.

Acknowledgement: The authors express their sincere gratitude to Dr. Rahul Warke (Director, Microbiology Department) and Dr. Girish Mahajan (Senior Vice President, Microbiology Department) for their exceptional scientific guidance, critical insights, and continuous support throughout the development of this work. The authors also thank Ms. Vrutti Mistry (Scientific Writer) for her support in drafting the manuscript.