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Diversity and distribution of Klebsiella capsules in Escherichia coli

Nanayakkara, Buddhie S., O'Brien, Claire L., Gordon, David M.
Environmental microbiology reports 2019 v.11 no.2 pp. 107-117
Escherichia coli, Klebsiella, O-antigens, encapsulation, freshwater, genes, horizontal gene transfer, sequence homology, serotypes, Australia
E. coli strains responsible for elevated counts (blooms) in freshwater reservoirs in Australia carry a capsule originating from Klebsiella. The occurrence of Klebsiella capsules in E. coli was about 7% overall and 23 different capsule types were detected. Capsules were observed in strains from phylogroups A, B1 and C, but were absent from phylogroup B2, D, E and F strains. In general, few A, B1 or C lineages were capsule‐positive, but when a lineage was encapsulated multiple different capsule types were present. All Klebsiella capsule‐positive strains were of serogroups O8, O9 and O89. Regardless of the phylogroup, O9 strains were more likely to be capsule‐positive than O8 strains. Given the sequence similarity, it appears that both the capsule region and the O‐antigen gene region are transferred to E. coli from Klebsiella as a single block via horizontal gene transfer events. Pan genome analysis indicated that there were only modest differences between encapsulated and non‐encapsulated strains belonging to phylogroup A. The possession of a Klebsiella capsule, but not the type of capsule, is likely a key determinant of the bloom status of a strain.