The solution was autoclaved and, after cooling down to 50◦C,
the base medium was mixed with 80 ml of an egg yolk emulsion with potassium tellurite 0.15% (Laborclin Produtos para Laboratorios Ltda, Pinhais, PR, Brazil).
Potassium tellurite was used in the egg yolk emulsion to improve the visualization of the halos of precipitation and
the accuracy of measurements. Then, 5-μl aliquots of each cell suspension at 108 CFU/ml were inoculated on
the egg yolk medium and plates were incubated at 37oC for 7 d