QVprep Microbiology Lessons

Bacterial Growth



Complex media and chemically defined media: Complex media may be differentiated from chemically defined media in that the exact composition of defined media is known; complex media includes biological mixtures. Complex media includes ingredients with unknown composition; these include ingredients like brain-heart infusion and yeast extract.

Halophilic microorganisms: Halophilic microorganisms may be defined as bacteria that require high concentrations of sodium chloride. By definition, halophiles are those microbes that require NaCl for growth. Vibrio cholera is an example of halophilic organism. Vibrio species are associated with ocean, which typically has a concentration of approximately 3% NaCl.

Mannitol Salt Agar (MSA): Mannitol Salt Agar (MSA) is selective for Staphylococcus species and inhibitory to most microorganism. It has a 7.5% concentration of NaCl. While 7.5% is inhibitory to most species of bacteria, a 2% NaCl concentration is inhibitory to most bacteria as well. For perspective, note that 0.9% saline is isotonic to red blood cells.

Microbiological media: Microbiological media may be defined as substrates for microbiological growth. Microbiological media is used to cultivate (encourage the growth of) microbes in the laboratory.