The Bacterial Growth Curve
When conditions are right bacteria begin to multiply
· The increase in numbers is not uniform
· It passes through a number of phases:
Lag
· No multiplication, bacteria are producing necessary enzymes
· Lag phase may be considered as recovery period for bacteria subjected to unfavourable conditions, for example:
· Too: hot, cold, dry
· No oxygen
Logarithmic
Rapid multiplication (growth)
Stationary
· Number remains constant
· Number produced equals number dying
· Food has decreased
· Competition for space and food has increased
· Toxic waste products have increased killing some bacteria
Decline
· Number decreases
· Number dying exceeds number produced Competition
· Micro-organisms compete for space and food
· Food poisoning bacteria tend to be less competitive than natural flora. NB some doctors do not like prescribing antibiotics for salmonella food poisoning – they prefer to rely on competition from
natural bacteria in the intestines. Antibiotics tend to kill the protective gut bacteria, exposing attachment sites on the gut wall for invasive pathogens such as salmonella
· Could result in the person becoming a salmonella carrier