Question

Why is it difficult to destroy 72 hr old microbial culture than 24 hour culture?

Answer 1

A 24 hr microbial culture is in naive phase and depending on the volume of the culture it still might be in logarithmic or growing phase where it is growing and focusing solely on metabolizing and dividing. But, in a 72 hr microbial culture it generally is in stationary phase where the genes responsible for better survival are activated and functioning, cells getting better in surviving in the nutrient deprived state, even in long term stationary phase. There is a continuous evolution in the bacterial cells which somehow make them fitter and more fitter in that stage.