Complete-genome analysis reveals diverse and conserved antimicrobial resistance platforms in Enterobacterales from veterinary diagnostic cases in Saint Kitts and Nevis

Antimicrobial resistance surveillance frequently identifies resistance genes in veterinary bacterial isolates, but the plasmid and chromosomal architectures responsible for their maintenance and potential mobility are often incompletely resolved. Here, we used hybrid Illumina–Oxford Nanopore sequencing to resolve the chromosomes and plasmids of nine resistant Enterobacterales (five Escherichia coli , three Klebsiella pneumoniae , and one Klebsiella quasipneumoniae ) recovered from veterinary diagnostic cases involving dogs, cats, and captive African green monkeys in Saint Kitts and Nevis between 2016 and 2024. The isolates carried diverse β-lactamase genes, including bla CTX−M−2 , bla CTX−M−15 , bla CTX−M−27 , bla TEM−1 , bla TEM−206 and several bla SHV variants, along with determinants associated with resistance to aminoglycosides, tetracyclines, quinolones, and folate synthesis inhibitors. Resistance determinants occurred across diverse plasmid backbones, including IncF, IncH, IncI, IncN, and IncR, and were frequently associated with multidrug resistance regions and mobile genetic elements. Notably, an indistinguishable ~ 40-kb IncN plasmid carrying bla CTX−M−15 was identified in E. coli and K. quasipneumoniae recovered from captive African green monkeys. One E. coli isolate carried chromosomally integrated bla CTX−M−2 within a multidrug resistance region associated with a class 1 integron and insertion sequences. Consistent with the unusual nature of this finding, only 5.4% (9/168) of publicly available bla CTX−M−2 sequences identified in our analysis were chromosomally located. Comparative analyses further identified highly similar plasmid backbones among previously reported human, animal, food, and environmental isolates from geographically diverse locations. Complete genome reconstruction revealed diverse plasmid and chromosomal architectures underlying antimicrobial resistance in Enterobacterales recovered from companion animals and captive primates in the Caribbean, including resistance platforms with close homologs previously reported from diverse hosts and geographic settings. The occurrence of an indistinguishable IncN- bla CTX−M−15 plasmid in two Enterobacterales species and the uncommon chromosomal integration of bla CTX−M−2 illustrate distinct genomic contexts through which resistance determinants may be maintained. These findings demonstrate the value of plasmid-resolved genomic surveillance for characterizing antimicrobial resistance in animal-associated bacterial populations.