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Microbial Physiology

• Microorganisms encompass bacteria, actinomycetes, fungi, and cyanobacteria, each with unique traits.
• Most microorganisms lack chlorophyll however cyanobacteria and phototrophic bacteria derive energy from light.
• Heterotrophic microorganisms, which lack chlorophyll, rely on external sources for nutrition.
• Parasites obtain nutrients from living hosts.
• Saprophytes acquire nutrients from organic or dead matter.
• Microbial physiology studies microbial activities, functions, and their interactions with the environment.

Culture Media

• Microorganism propagation necessitates a suitable biochemical and biophysical setting.
• Heterotrophs utilize surrounding materials to sustain growth, protoplasm synthesis, and cellular activities.
• Essential elements like K, Mg, P, and S are absorbed as ions.
• Vitamin-deficient microorganisms utilize vitamins from the media.
• Culture media are vital for microorganism isolation, maintenance, and identification.
• Liquid media support biomass production and physiological studies.
• Solidified media are used for isolating pure cultures, morphological studies, and diverse applications.

Types of Culture Media

• Culture media are grouped based on composition or application.

Natural Media

• Complex media have unknown chemical compositions.
• Complex media contain biological materials like blood, milk, yeast extract, beef extract, or plant extracts with undetermined chemical composition
• They are commonly used for microorganism isolation and morphological studies, particularly in the solidified state.
• Complex media supply a wide array of growth factors.

Semisynthetic Medium

• Semisynthetic media have some components with defined chemical compositions mixed with complex sources that have unknown compositions
• They are valuable in microbial isolation.
• Potato-dextrose agar is a common semisynthetic medium.

Synthetic (Defined) Medium

• Synthetic media have a precisely known chemical composition.
• Used for studying microorganismal nutritional needs, enrichment cultures, and physiological research.
• Microbial growth and reproduction can be slower in synthetic media compared to complex media.
• Adding 20 mg/L of peptone or yeast extract can enhance growth.

Selective and Differential Media

• Culture media are constructed on the principles of selection and enrichment
• Selective media contain components that inhibit certain microorganisms while promoting the growth of desired species, especially in bacteria.
• Temperature and pH adjustments can enhance selectivity.
• Differential media help microbiologists distinguish between bacteria types.
• Staphylococcus aureus, a common bacterial pathogen, can be identified using a high salt concentration, mannitol (a fermentable sugar), and a pH indicator dye.
• Mannitol-fermenting S. aureus colonies produce acid, react with the dye, and form colored halos.
• Mannitol non-fermenters like S. epidermidis do not create halos.