Years ago we were encouraged to switch from traditional soap to new liquid soap and body wash. Besides the argument that they were more convenient, the biggest marketing message was that these new liquid versions were more hygienic. Their premise at the time was that lots of people would use the same bar of soap, thus leaving bacteria from their hands on the bar, ready for the next person to use it.
However, over the years, numerous studies have disproved this theory. The London School of Hygiene and Tropical Medicine states that bar soaps are a hostile environment for bacteria.
The bacterial cells get exploded by the strong chemical concentrations. There is no risk of bugs being passed from one person to another via a bar of soap.
Researchers deliberately coated their hands with five BILLION bacteria, including E.Coli before washing them with a bar of soap. A second person then washed with the same bar of soap, but tests showed the bacteria didn't show up on their hands.
Bacteria need 4 things to grow. Food source, water/moisture, time, and heat.
1 bacterium can multiply itself (division) every 20 mins in these conditions.
Bacteria would struggle to live on or in any bar or bottle of soap, there is little food to help.
You are more likely to transmit bacteria to the plastic pump of a bottle of hand soap than to a bar of soap, as the plastic is a much less hostile environment to bacteria.
Another thing to consider is although soap contains fats and oils, a food source, they're no longer food, after saponification. Without a food source, no growth. Bacterium live longer inside and on us than any other surface!