Detection of Paenibacillus larvae subspecies larvae spores in naturally infected bee larvae and artificially contaminated honey by PCR

American foulbrood (AFB), a severe bacterial disease of honeybee brood, has recently been found in Uruguayan apiaries. Detection of the causative agent, Paenibacillus larvae subspecies larvae, is a very important concern in order to prevent disease dissemination and decrease of honey production. Since spores are the infective forms of this pathogen, in the present work we report the use of polymerase chain reaction (PCR) to detect P. l. subsp. larvae spores from in vitro cultures, larvae with clinical symptoms and experimentally contaminated honey. The set of primers was designed based on the published P. l. subsp. larvae 16S rRNA gene. Using this approach we could amplify the pathogen DNA and obtain a great sensitivity and a notable specificity. Detection limit for spore suspension was a 10^–2 dilution of template DNA obtained from 32 spores, as determined by plate count. For artificially contaminated honey, we could detect the PCR product at a 10^–3 dilution of template DNA obtained from 170 spores. In addition, when PCR conditions were set to improve specificity, we were able to amplify P. l. subsp. larvae DNA selectively and no cross-reactions were observed with a variety of related bacterial species, including P. l. subsp. pulvifaciens. Since spore detection is very important to confirm the presence of the disease, this method provides a reliable diagnosis of AFB from infected larvae and contaminated honey in a few hours.