Summary 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.
During bloom events, Escherichia coli cell counts increase to between 10,000 and 100,000 cfu/100 ml of water. The strains responsible for bloom events belong to E. coli phylogenetic groups A and B1, and all have acquired a capsule from Klebsiella. A pan-genome comparison of phylogroup A E. coli revealed that the ferric citrate uptake system (fecIRABCDE) was overrepresented in phylogroup A bloom strains compared with non-bloom E. coli. A series of experiments were carried out to investigate if the capsule together with ferric citrate uptake system could confer a growth rate advantage on E. coli. Capsulated strains had a growth rate advantage regardless of the media composition and the presence/absence of the fec operon, and they had a shorter lag phase compared with capsule-negative strains. The results suggest that the Klebsiella capsule may facilitate nutrient uptake or utilization by a strain. This, together with the protective roles played by the capsule and the shorter lag phase of capsule-positive strains, may explain why it is only capsule-positive strains that produce elevated counts in response to nutrient influx. ; Tel.: 61 2 6125 3552.
Open dumping of hospital and livestock waste pollutes soils and water with antibiotics, thus allowing open landfill sites to be lavish breeding grounds for antibiotic-resistant bacteria (ARB). The study investigates the antibiotic sensitivity of soil bacteria isolated from a major municipal solid waste landfill site (Gohagoda) in the Central Province of Sri Lanka, which is located close to the river Mahaweli, the main water source for residents of Kandy, the main city of the Central Province, and its immediate suburbs. Dominant bacterial isolates from soils of the Gohagoda landfill site (polluted, PO) and a nearby wooded area (relatively unpolluted, UP) were tested for antibiotic sensitivity against amikacin, amoxicillin-clavulanate, ciprofloxacin, cefotaxime, imipenem, meropenem and ticarcillin-clavulanate. The results were analyzed using t-test and z-test in Minitab 18.1. Mean diameters of inhibition zones of soil bacterial isolates from UP were significantly higher than those of PO for all antibiotics except for meropenem. The percentage of isolates resistant to all antibiotics was higher in PO compared to UP, except for amikacin and cefotaxime. The findings show a higher prevalence of ARB in the Gohagoda landfill site, emphasizing the importance of identifying alternative measures to dispose municipal solid waste and to introduce proper sanitation practices among landfill workers. Testing soil leachates for ARB is imperative to confirm any threats to the nearby water source.
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