Mesophilic

Mesophiles are organisms that grow best at moderate temperatures. In microbiology, the term is typically applied to bacteria, archaea, and some fungi whose optimum growth temperature lies between about 20°C and 45°C. For many mesophiles, growth is most rapid near human body temperature, around 37°C.

Mesophiles sit between psychrophiles (cold-loving) and thermophiles (heat-loving). They typically have an optimum growth range around 20–45°C, with many species peaking near 30–37°C. Some organisms tolerate a broader range, but their performance remains better in this moderate temperature band.

Habitat and examples of mesophiles are diverse. They occur in soil, water, decaying matter, plants, and animal-associated environments, including the human microbiota. In food science, mesophilic cultures drive many fermentation processes. Common mesophilic bacteria include species such as Escherichia coli and Staphylococcus aureus, and yeasts such as Saccharomyces cerevisiae are also considered mesophilic.

Practical significance involves managing their growth. Temperature control is a key method in medicine and food safety to slow or inhibit mesophilic proliferation. Refrigeration slows growth, while heat treatment or pasteurization can inactivate many mesophiles. Growth is also influenced by factors such as pH, water activity, oxygen availability, and nutrient presence.