Salmonella and e-Coli affect both people and reptiles, but they are easily avoided by washing your hands after handling your critter. Since transmission is fecal-oral I don't think you have to worry about your snakes picking either up from you.
+1
My fiance was worried about this also when I was first interested in snakes and this is what all of my research showed.
The important thing is not to stop questioning. Curiosity has its own reason for existing.