Phenotypic characterization and ERIC-PCR based genotyping of Paenibacillus larvae isolates recovered from American foulbrood outbreaks in honey bees from Italy.

ABSTRACT

BACKGROUND: Paenibacillus larvae is the etiological agent of American foulbrood (AFB), a widespread and severe bacterial brood disease of honey bees. The genomic characterization of P. larvae strains by enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) is able to differentiate four genotypes (ERIC I, ERIC II, ERIC III, ERIC IV). The information on the presence of P. larvae ERIC genotypes worldwide is few. OBJECTIVES: We have characterized P. larvae strains isolated in Italy from AFB outbreaks to obtain information on ERIC genotypes and phenotypes of the strains circulating in the country. METHODS: A total of 117 P. larvae isolates from 115 AFB outbreaks occurring in 2008-2012 were subjected to phenotypic and genetic characterization. RESULTS: The genomic characterization allowed the identification of ERIC I and ERIC II genotypes. Examining the data of Northern and Central Italy separately it was noted that in Northern Italy most outbreaks were caused by the ERIC I genotype (78.6%), followed by the ERIC II genotype (18.6%) and by co-infections (ERIC I + ERIC II) (2.6%). In Central Italy, only outbreaks caused by the ERIC I genotype were observed. With regard to phenotypic characteristics all examined strains of ERIC II genotype fermented fructose while no strains of ERIC I genotype possessed this ability. CONCLUSION: Both P. larvae ERIC I and ERIC II genotypes were isolated from the AFB outbreaks, but ERIC II genotype was isolated only in Northern Italy. The fermentation of fructose seems to be a genotype-specific biochemical marker.