$BACKGROUND$: $Klebsiella\; pneumoniae$ is a gram-negative bacterial species capable of occupying a broad range of environmental and clinical habitats. Known as an opportunistic pathogen, it has recently become a major causative agent of clinical infections worldwide. Despite growing knowledge about the highly diverse population of $K.\; pneumoniae$, the evolution and clinical significance of environmental $K.\; pneumoniae$, as well as the relationship between clinical and environmental $K.\; pneumoniae$, are poorly defined.

$METHODS$: We isolated and sequenced $K.\; pneumoniae$ from in-patients in a single hospital in Thailand, as well as hospital sewage, and surrounding canals and farms within a 20-km radius.

$RESULTS$: Phylogenetic analysis of 77 K. pneumoniae (48 clinical and 29 non-clinical isolates) demonstrated that the two groups were intermixed throughout the tree and in some cases resided in the same clade, suggesting recent divergence from a common ancestor. Phylogenetic comparison of the 77 Thai genomes with 286 $K.\; pneumoniae$ from a global collection showed that Thai isolates were closely related to the clinical sub-population of the global collection, indicating that Thai clinical isolates belonged to globally circulating lineages. Dating of four Thai $K.\; pneumoniae$ clades indicated that they emerged between 50 and 150 years ago. Despite their phylogenetic relatedness, virulence factors and β-lactamase resistance genes were more numerous in clinical than in environmental isolates. Our results indicate that clinical and environmental $K.\; pneumoniae$ are closely related, but that hospitals may select for isolates with a more resistant and virulent genotype.

$CONCLUSIONS$: These findings highlight the clinical relevance of environmental K. pneumoniae isolates.