Identification and Onion Pathogenicity of Burkholderia cepacia Complex Isolates from the Onion Rhizosphere and Onion Field Soil

Abstract

Burkholderia cepacia complex strains are genetically related but phenotypically diverse organisms that are important opportunistic pathogens in patients with cystic fibrosis (CF,) as well as pathogens of onion and banana, colonizers of the rhizospheres of many plant species, and common inhabitants of bulk soil. Genotypic identification and pathogenicity characterization were performed on B. cepacia complex isolates from the rhizosphere of onion and organic soils in Michigan. A total of 3,798 putative B. cepacia complex isolates were recovered on Pseudomonas cepacia azelaic acid tryptamine and trypan blue tetracycline semiselective media during the 2004 growing season from six commercial onion fields located in two counties in Michigan. Putative B. cepacia complex isolates were identified by hybridization to a 16S rRNA gene probe, followed by duplex PCR using primers targeted to the 16S rRNA gene and recA sequences and restriction fragment length polymorphism analysis of the recA sequence. A total of 1,290 isolates, 980 rhizosphere and 310 soil isolates, were assigned to the species B. cepacia (160), B. cenocepacia (480), B. ambifaria (623), and B. pyrrocinia (27). The majority of isolates identified as B. cepacia (85%), B. cenocepacia (90%), and B. ambifaria (76%) were pathogenic in a detached onion bulb scale assay and caused symptoms of water soaking, maceration, and/or necrosis. A phylogenetic analysis of recA sequences from representative B. cepacia complex type and panel strains, along with isolates collected in this study, revealed that the B. cenocepacia isolates associated with onion grouped within the III-B lineage and that some strains were closely related to strain AU1054, which was isolated from a CF patient. This study revealed that multiple B. cepacia complex species colonize the onion rhizosphere and have the potential to cause sour skin rot disease of onion. In addition, the onion rhizosphere is a natural habitat and a potential environmental source of B. cenocepacia.

Burkholderia cenocepacia J2315-mediated destruction of Staphylococcus aureus NRS77 biofilms.

“…The Burkholderia cepacia complex (Bcc) consists of 18 related Gram-negative species that thrive in a diverse array of environmental niches and have a broad array of metabolic capabilities, including nitrogen fixation [71], pollutant metabolism [72,73], antifungal production [74], and plant pathogenesis [75]. These bacteria are typically found in the soil or water, and this versatility seen in Bcc ecological specialization is attributable to their uniquely complex genomes.…”

Antibiotic resistant bacteria in natural environments within Kentucky.

“…The gloves being worn, the onions, and the bench top were sprayed with 70% ethanol for sterilization. This method was described in Jacobs et al [18]. The onions were cut in quarters with a kitchen knife, which had been disinfected with 70% ethanol.…”

“…Each bacterial isolate were inoculated into three adjacent onion peels to produce triplicates. The acrylic bin was covered with Saran wrap or aluminum foil and incubated at 37°C for approximately 48 hours as described in Jacobs et al [18]. The positive control was Burkholderia cepacia strain ATCC 25416 (a known onion pathogen) [18], and the negative controls were Pseudomonas sp.…”

“…The data obtained were analyzed by comparing pictures of the onion peels before incubation and at the end of the incubation period (Supplementary Figure 3) and rated on a scale of 0 (no maceration) to 3 (massive tissue destruction) based on published protocols [18].…”

“…To test the pathogenicity of the representative panel isolates for the ability to cause pathogenesis in two plant models -onion bulb and lettuce leaves, the isolates were inoculated into sterile onion peels and lettuce cores as described in the Materials and Methods section according to published protocols [18,37].…”