Mycoplasma hominis

Every now and then, mycoplasma contamination rears its ugly head and threatens tissue culture experiments. According to a paper in the Journal of Cell Science (albeit published in 1966), the most common variety of mycoplasma found in contaminated cultures is M. hominis type 1. Mycoplasma hominis is most commonly found in the genital area. What are these people doing with their cultures to get them infected?