Klebsiella pneumoniae is an opportunistic pathogen that can cause severe infections in humans and also in animals. K. pneumoniae with different colony morphologies, different antibiotic and bacteriophage susceptibilities and different pulsed-field gel electrophoresis profiles were isolated from two samples from a horse with a respiratory infection. Ten representative isolates were sequenced (Illumina NextSeq), reads were assembled using different methods and contigs analysed. Different plasmid combinations in the set of isolates and the availability of suitable reference plasmids made it possible to predict plasmid sequences. PCR was used to confirm the arrangement of backbone contigs, but the order of multiple IS26 flanked regions has not been defined conclusively. The 10 isolates belong to five different sequence types (ST), four of which are important in human infections. Seven isolates belonging to these four ST appear to share the same novel HI-type plasmid, which may have spread between them during the course of the infection. Most isolates of four ST have a plasmid related to F-type plasmids named pKPN-307, originally identified in ST307. The longest version, pKPN-307A carries a heavy metal resistance cluster and five regions potentially contributing to virulence. Plasmids in three ST307 horse isolates carry all of these regions and 11 antibiotic resistance genes, including blaCTX-M-15. All three ST628 isolates have a plasmid with a backbone closely related to these, but only a subset of the resistance genes. Plasmids in the single ST392 and single ST4656 isolates have similar resistance regions to the ST307 plasmids but differences in the backbone. Two ST893 isolates have a distinct F-type plasmid that carries some of the same resistance genes as plasmids in other ST. Differences between the pKPN-307 plasmids, including some subtle variations in resistance regions, do not appear compatible with spread between ST during the infection.