Tests showed that three brands of soap commercially sold to generate bubbles for children contained large numbers of bacteria. Viable counts averaged 5 × 106 colony forming units (CFU) of bacteria per milliliter in 55 samples from three brands and ranged from 10 to 108 CFU/ml.
Pseudomonas aeruginosa was the most frequently isolated organism. Escherichia coli, Alcaligenes faecalis, Enterobacter species, Staphylococcus albus, Klebsiella species, Corynebacterium species, and Sarcina lutea were also detected. Results indicated that Pseudomonas contamination occurred at the site of assembly and not in retail stores.
McGarrity GJ, Coriell LL. Bacterial Contamination of Children's Soap Bubbles. Am J Dis Child. 1973;125(2):224–226. doi:10.1001/archpedi.1973.04160020056010