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Cultivation of Yeasts & Molds


The Total Yeast & Mold Count

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An Indicator of the Microbial Safety of Products

To determine the total yeast and mold count (TYMC) in raw materials, water and finished pharmaceutical and cosmetics products, Merck provides a comprehensive range of selective, granulated dehydrated culture media (DCM).

The Total Yeast & Mold Count to Assess the Microbiological Safety of Products

The total yeast and mold count (TYMC) is a test to detect mesophilic fungi in pharmaceutical ingredients that range from raw materials and water to the finished products. It is part of the qualitative phase of bioburden testing (including microbial limit testing) to determine the presence or absence of specific microorganisms. For pharmaceutical and cosmetics manufacturers it is very important from a safety perspective to ensure that their products are free from hazardous microbes such as yeasts and molds.

Another part of microbial enumeration is the total aerobic microbial count (TAMC). It is used for determining the total count of aerobic bacteria.

Culture Media to Determine the TYMC

Merck provides a wide range of media for the enrichment, isolation and enumeration of yeasts and molds and for the preparation of the TYMC test, the total yeast and mold count.

Merck’s uniquely granulated culture media are both convenient and safe. They meet the highest industry performance standards that ISO 11133 stipulates. When used in the lab, the granulated media cause significantly less dust than powdered ones, which leads to less inhalation of hazardous media components that cause allergic responses. It also minimizes contamination of the work environment.

All Merck media are quality controlled according to stringent standards, thereby guaranteeing the consistent high quality of our products.

Yeast and Molds

Yeast & Molds

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Approximately 1,500 species of yeasts are currently known. They are unicellular, although some species may become multicellular through the formation of so-called pseudohyphae, or false hyphae. Yeast cell sizes can vary greatly depending on the species, though they typically measure 3 to 4 µm in diameter. Most yeast species reproduce asexually by mitosis, and many do so by an asymmetric process called budding.

Yeasts as Human Pathogens

Some yeast species are opportunistic pathogens that can cause infections in humans whose immune systems are compromised. Cryptococcus neoformans is a noteworthy such pathogen, causing the disease called cryptococcosis. Yeast cells are surrounded by a rigid capsule of polysaccharides, which helps to prevent them from being recognized by the immune system of humans. Yeasts of the genus Candida, another group of opportunistic pathogens, cause oral and vaginal infections in humans, a condition known as candidiasis. Candida occurs as a commensal yeast in the mucus membranes of humans. The same strains, however, can become pathogenic under certain circumstances.

Cultivation of Yeasts in the Laboratory

Yeasts can be grown in the laboratory on solid culture media or in liquid broths. Typical media used for the cultivation of yeasts include potato dextrose agar or broth, Wallerstein nutrient agar, yeast peptone dextrose agar, and yeast mold agar or broth.

Molds are a large and taxonomically diverse group. They grow as multicellular filaments called hyphae. The network of a mold’s hyphae is considered a single organism and called a mycelium. There are thousands of known species with a wide range of lifestyles but all requiring moisture for growth. They include saprotrophs, mesophiles, psychrophiles and thermophiles.

Molds as Pathogens

High levels of airborne mold spores can cause allergic reactions, asthma episodes, irritations of the nose, eye and throat, sinus congestion, as well as other respiratory problems. When mold spores are inhaled by an immunocompromised person, some of these spores may start to grow on living tissue, attach to cells along the respiratory tract and cause further problems.

Granulated Dehydrated Culture Media Video

Granulated Dehydrated Culture Media

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