ERIC-PCR Genotyping of Paenibacillus larvae in Southern Italian Honey and Brood Combs

Comparative analysis of Paenibacillus larvae genotypes isolated in Connecticut

Ninety-six strains of Paenibacillus larvae, causative agent of American foulbrood in honey bee (Apis mellifera) larvae, collected from Connecticut, USA (CT), honey bees, and 12 P. larvae strains not from CT, were genotyped via ERIC-PCR and XbaI-RFLP analysis. All CT-isolates, five strains isolated in South America, three strains from North America (not CT), and one strain isolated in Australia grouped into the ERIC I genotype. Three P. larvae formerly subsp. pulvifaciens strains grouped into ERIC III and IV genotypes. XbaI-RFLP genotyping showed three genotypes within the CT-isolates, and two were identified as XbaI-RFLP Type I and III. The third XbaI-RFLP genotype (Type Ib) represented one of four new XbaI-RFLP genotypes identified. Comparison of genotype results for the P. larvae strains tested was used to develop a correlation between ERIC-PCR genotyping and XbaI-RFLP genotyping. Sixteen CT-isolates were tetracycline-resistant and demonstrated PCR amplification using oligonucleotide primers for tetL. All 16 isolates grouped within XbaI-RFLP Type Ib, suggesting limited introduction of a tetracycline-resistant strain into CT.

Biogeography of Paenibacillus larvae, the causative agent of American foulbrood, using a new multilocus sequence typing scheme

American foulbrood is the most destructive brood disease of honeybees (Apis mellifera) globally. The absence of a repeatable, universal typing scheme for the causative bacterium Paenibacillus larvae has restricted our understanding of disease epidemiology. We have created the first multilocus sequence typing scheme (MLST) for P. larvae, which largely confirms the previous enterobacterial repetitive intergenic consensus (ERIC)-polymerase chain reaction (PCR)-based typing scheme's divisions while providing added resolution and improved repeatability. We have used the new scheme to determine the distribution and biogeography of 294 samples of P. larvae from across six continents. We found that of the two most epidemiologically important ERIC types, ERIC I was more diverse than ERIC II. Analysis of the fixation index (FST ) by distance suggested a significant relationship between genetic and geographic distance, suggesting that population structure exists in populations of P. larvae. Interestingly, this effect was only observed within the native range of the host and was absent in areas where international trade has moved honeybees and their disease. Correspondence analysis demonstrated similar sequence type (ST) distributions between native and non-native countries and that ERIC I and II STs mainly have differing distributions. The new typing scheme facilitates epidemiological study of this costly disease of a key pollinator.

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

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.

Molecular typing of Paenibacillus larvae strains isolated from Bulgarian apiaries based on repetitive element polymerase chain reaction (Rep-PCR)

The aim of the present study was to perform molecular typing of Paenibacillus larvae (P. larvae) isolates from Bulgarian apiaries with repetitive element polymerase chain reaction (rep-PCR) using BOX A1R, MBO REP1, and ERIC primers. A total of 96 isolates collected from brood combs with clinical symptoms of American foulbrood originating from apiaries located in different geographical regions of Bulgaria, a reference strain P. larvae NBIMCC 8478 and 30 commercial honey samples with Bulgarian origin were included in the study. Rep-PCR fingerprinting analysis revealed two genotypes ab and AB of P. larvae isolates from brood combs and honey samples. A combination of genotypes ab/AB was detected in one apiary and honey sample. The prevailing genotype ab was found in 78.1 % of brood combs isolates as well as in the reference strain whereas genotype AB was determined in 21.9 % of isolates. The examination of honey samples confirmed the preponderance of ab genotype which was demonstrated in 20 of 30 samples analyzed. In conclusion, the genetic epidemiology of P. larvae revealed two genotypes--ab and AB for Bulgarian strains. Developed protocols for molecular typing of P. larvae are reliable and may be used to trace the source of infection.