The amount of time it takes for a cell to reproduce is called generation time.  Each different species has its own generation time.  Some bacteria, such as E. coli and Staphylococcus aureus have very short generation times, while others, such as Mycobacterium leprae, may take as long as 10 days.  Because many food-borne pathogens replicate very quickly, special care must be taken to refrigerate hot food soon after a meal to slow down microbial growth.