A simple and sufficiently sensitive test for the presumptive detection of antibiotics in foods has been developed, based on the principle that the food under investigation is mixed with double‐strength agar containing triphenyltetrazolium chloride as an indicator of bacterial growth. The agar dispersion so obtained is streak‐inoculated with suitable test strains and incubated, using as a blank a mixture of agar and an identical food sample known to be free from added antibiotics.
For the presumptive detection of antibiotics Staphylococcus aureus and Streptococcus cremoris are used as test organisms. For use in the confirmative and completed tests the usual selection of test bacteria and strains, which have been rendered resistant to a certain antibiotic, may be used.