What is the reason for bacterial death in the cell culture? Will bacteria spontaneously die in human infection?

Question

Discussing microbiology lab on bacterial growth curve

Answer 1

In general, bacteria die in a culture due to either exhaustion of nutrients (broadly defined) or accumulation of waste products (or, you stress the culture in other ways -- add a poison, add a phage, overheat the dish, etc). Usually the human organism provides adequate nutrients (otherwise, why would growth have initiated?), and said waste products are more toxic to the human organism than to the bacteria. Therefore, said bacteria need a bit of active interference by the human physiology to be killed off -- an antibody, ingestion by macrophages, etc. You would not consider this "spontaneous death". And related to this, is the fine line to be drawn between normal commensal organism activity, and pathogenicity. A slight change in the human general condition -- stress from lack of sleep while studying for exams, change of diet, unusual heat or cold stress, etc. -- may render you prone to infections, including from your normal flora organisms. (see "saiga dieoff", for example).

-- Cheers, -- Mr. d.