Limited similarity between plasmids encoding CTX-M-1 β-lactamase in Escherichia coli from humans, pigs, cattle, organic poultry layers and horses in Denmark.

The research investigates the epidemiological relationship between CTX-M-1-producing E. coli found in humans and animals in Denmark from 2006 to 2010. The researchers concluded that CTX-M-1 in human E. coli infections in Denmark during the study period might be minimally influenced by animals.

Research Methodology

• The study analysed 65 CTX-M-1-producing isolates derived from various sources – patients (22), pigs (21), cattle (4), organic poultry layers (3) and horses (15).
• The researchers employed pulsed-field gel electrophoresis (PFGE) to type these isolates.
• Further characterisation of the plasmids harbouring the bla gene (a gene implicated in antibiotic resistance) was accomplished through various methods such as S1 PFGE, PCR-based replicon typing, plasmid multilocus sequence typing, restriction fragment length polymorphism, and sequencing.

Findings

• The researchers found that the human and animal strains of E. Coli were unrelated based on PFGE.
• They observed a higher frequency of IncI1 in human isolates (13 out of 22) than in animal isolates (7 out of 43), whereas IncN was found to be more common among animal isolates (24 out of 43 versus 5 out of 22 in humans).
• The full characterisation of the plasmids containing the bla gene revealed host-specific patterns in their distribution. For instance, specific IncI1, IncN and IncH1 plasmid subtypes were predominantly found in humans, livestock and horses, respectively.
• One notable discovery was three identical human, bovine and porcine IncI1/ST49 plasmids. They all had high nucleotide sequence homology but differed by the presence of IS66 elements in the bovine plasmid and the absence of one gene within the microcin-encoding operon in the human plasmid.

Conclusions

• The research infers a minor contribution by animals to the occurrence of CTX-M-1 in human E. coli infections in Denmark during the study period. This suggests that the E. coli strains in humans aren’t largely derived from animal sources but could be resulting from other causes that need further investigation.