One possible reason for the growth of these strains on latex overlay agar is the presence of impurities or organic compounds that were not removed completely from the purified latex.
Crude latex contains proteins, carbohydrates, lipids, amino acids and inorganic compounds other than polyisoprene and water [27].
Such natural impurities might also be present in the latex samples.
These impurities may serve as the growth substrates for bacteria that do not have the ability to use latex.