We analyzed the ability of extraintestinal strains of Enterobacter spp. and Citrobacter spp. to employ different siderophore-mediated strategies of iron acquisition. All strains produced iron-chelating compounds. Cross-feeding assays indicated that most isolates of both Enterobacter spp. and Citrobacter spp. excreted catecholate siderophore enterobactin, less produced aerobactin, and single strains excreted hydroxamates different from aerobactin. Besides, we analyzed if the strains had the ability to produce the siderophore yersiniabactin coded by the Yersinia high-pathogenicity island (HPI). The presence of HPI genes was observed in single isolates of three species: E. cloaceae, E. aerogenes and C. koseri. A detailed polymerase chain reaction analysis revealed differences in the genetic organization of the HPIs; however, in a cross-feeding test we proved that yersiniabactin was produced and the island was functional.

Two probiotics, Biogen-N and Trilac, were used as supplements to pollen substitute in feeding honey bees, Apis mellifera. The probiotics were given either throughout the entire 14-day experiment or only for 2 days, just after bee emergence. The midgut of worker bees was colonized by bacteria present in probiotics, including Lactobacillus spp., Pediococcus acidilactici, Bifidobacterium bifidum and Enterococcus faecium. Advantages of probiotic supplementation include better bee survival and higher dry mass and crude fat level in comparison with bees fed with pollen substitute only. We did not observe significant differences in total protein in the dry mass of bees. There was no correlation between the duration of feeding with probiotics and the chemical composition of the bees. This suggests that to achieve an increase in dry mass and crude fat level, it is sufficient to supply probiotics only in the beginning of the feeding period, directly after bee emergence.