To grow (culture) microorganisms in the laboratory they must be given a suitable culture medium and suitable conditions.Culture media contain the nutrients the organisms need: a carbon source (often glucose), a nitrogen source (amino acids or proteins), minerals, and sometimes vitamins. The medium can be:
• nutrient broth, a liquid, usually in a bottle or flask, or
• nutrient agar, a jelly poured into Petri dishes, which gives a solid surface.Inoculating the medium: microorganisms are transferred with a sterile wire inoculating loop, a sterile pipette or a spreader.
• Streak plate: the loop is drawn across the agar in zig-zags, so the cells thin out and grow into separate colonies. Each colony comes from a single cell.
• Spread plate: a small volume of broth culture is spread evenly over the agar with a sterile spreader, giving an even lawn of growth if the culture is concentrated.
Growth conditions
• Temperature: enzymes work fastest at an optimum. In school labs cultures are incubated at about 25 °C, not 37 °C, to reduce the risk of growing human pathogens.
• pH: most bacteria grow best near neutral pH.
• Oxygen: many microorganisms need oxygen for aerobic respiration.
• Nutrients and water must be available.Growth can be measured by counting colonies, by counting cells with a haemocytometer, or by measuring the turbidity (cloudiness) of a broth with a colorimeter.
• nutrient broth, a liquid, usually in a bottle or flask, or
• nutrient agar, a jelly poured into Petri dishes, which gives a solid surface.Inoculating the medium: microorganisms are transferred with a sterile wire inoculating loop, a sterile pipette or a spreader.
• Streak plate: the loop is drawn across the agar in zig-zags, so the cells thin out and grow into separate colonies. Each colony comes from a single cell.
• Spread plate: a small volume of broth culture is spread evenly over the agar with a sterile spreader, giving an even lawn of growth if the culture is concentrated.
Growth conditions• Temperature: enzymes work fastest at an optimum. In school labs cultures are incubated at about 25 °C, not 37 °C, to reduce the risk of growing human pathogens.
• pH: most bacteria grow best near neutral pH.
• Oxygen: many microorganisms need oxygen for aerobic respiration.
• Nutrients and water must be available.Growth can be measured by counting colonies, by counting cells with a haemocytometer, or by measuring the turbidity (cloudiness) of a broth with a colorimeter.