Molecular epidemiology of Paenibacillus larvae infection in Finland

The epidemiology of a Paenibacillus larvae infection, causing American Foulbrood (AFB), was studied regionally in Finland and temporally in the apiaries. Altogether 156 P. larvae isolates from honey or brood samples supplied by 114 beekeepers were analysed by NotI pulsed-field gel electrophoresis (PFGE) and biotyping, as well as for tetracycline resistance. Fifty-two NotI macrorestriction profiles (MRP) and three biotypes were detected. All isolates were susceptible to tetracycline. Most MRPs and biotypes IV and V were widely spread throughout the country, though a few MRPs and biotype I were clustered around certain areas. Analysis of subsequent isolates from 25 beekeepers usually showed persistence of the infection in the apiaries, but in six cases unrelated infections emerged. Typing of contemporary isolates from one beekeeper revealed the presence of the same infection in distant apiaries, thus indicating that the spread of infection was through apicultural practices instead of neighbourhood. NotI PFGE allowed efficient strain discrimination and can be recommended for epidemiological surveillance of AFB.