Some live by the belief that when you drop a bit of food on the floor, you get five-seconds before it’s rendered too disgusting to eat. Six-seconds? No way! But for some reason five seconds has generally been accepted.
Biology students at Aston University in the UK monitored how quickly E.coli and common bacteria spread from surfaces to food such as toast (butter side down, no doubt), pasta and sticky sweets — with time being a significant factor in the transfer of germs.
Food picked up just a few seconds after being dropped is less likely to contain bacteria than if it is left for longer periods of time according to the findings.
The National Negawatt Exchange 
I did many years of research on this when I was a kid.