Bacterial Cultures Bacteria grow best in warm moist

Bacterial Cultures *Bacteria grow best in warm, moist, dark areas that contain a lot of food. -When we culture bacteria, we provide them with this environment to grow in via a Petri dish containing nutrient agar. Culture – growing a sample of bacteria in a laboratory. Petri dish – plastic container in which bacterial colonies are grown on nutrient agar. Nutrient agar – gel-like substance that provides bacteria with food, water, and moisture. Is its major food source.

Sterile vs. Contaminated -Before a Petri dish is opened, it is sterile. -As soon as it is exposed to the air, it becomes contaminated. Sterile – no bacteria are present. Contaminated – when unwanted bacteria enters the Petri dish.

Inoculating and Incubating -In order to grow bacteria, we take a sample from an object using a sterile Q-tip, inoculate the Petri dish, and incubate the sample over time. Inoculate – place desired bacteria into Petri dish using a sterile Q-tip. Incubate – place in an area to keep warm.

Streaking Petri Dishes

Bacterial Growth -Bacterial growth can be seen growing on nutrient agar in the form of colonies. Colonies – many bacteria growing close together.

Growth curve of bacteria culture j Lag phase: slow growth (adjust to environment) k Exponential phase: rapid growth l Stationary phase: reproduction = death rate m Death phase: death rate > reproduction rate 3 2 1 4

Zones of Inhibition *Scientists use bacterial colonies to test the effectiveness of new antibiotics and antimicrobial agents such as disinfectants and antiseptics. Zone of Inhibition – a clear region around paper discs that are saturated with an antimicrobial agent on the agar’s surface.