Detection of Bacillus larvae spores in Argentinian honeys by using a semi-selective medium

A semi-selective medium for the detection in Argentinian honeys of spores of Bacillus larvae, a pathogen of American foulbrood, was developed. The technique involves dilution of samples (1:2) in phosphate buffer, concentration of spores by centrifugation and heat treatment prior to inoculation. Two media (JNxPa and JNxPb) were prepared from J-agar, to which nalidixic acid and pipemidic acid were added. Both JNxP media were reliable for the isolation of B. larvae colonies and, at the same time, prevented the development of other Bacillus species which normally develop on the plates before B. larvae spores can germinate.