Abstract: Klebsiella spp. is an important human and animal pathogen, and it is commonly found with resistance to clinically important antimicrobials worldwide. The main goals of this study were to determine the prevalence of antimicrobial resistance genes in our study population and to assess the relatedness between Klebsiella spp. isolated from humans and animals. Isolates were collected in 2019 and 2020 from various animal hosts that presented to veterinary hospitals in the U.S. that participate in the FDA's Center for Veterinary Medicine Veterinary Laboratory Investigation and Response Network's antimicrobial resistance monitoring program. Results: We sequenced a total of 204 Klebsiella spp. isolates. A majority of isolates were identified as K. pneumoniae (149/204, 73.0%), followed by K. quasipneumoniae (30/204, 14.7%), K. variicola (15/204, 7.4%), K. aerogenes (5/204, 2.5%), K. oxytoca (4/204, 2.0%), and K. grimontii (1/204, 0.5%). Out of 204 isolates, 138 were recovered from dogs, 25 from horses, 17 from cats, 6 from avian species, 5 from cows and 3 from pigs. The remaining 10 isolates were recovered from a few other mammal species. Klebsiella spp. isolates were very diverse. In silico multilocus sequence typing (MLST), using WGS data, identified a total of 88 known sequence types across all isolates. Seventeen isolates were not assigned an MLST sequence type due to combinations of alleles not previously found in the PubMLST database. 45 of the 204 isolates were assigned to 20 different single nucleotide polymorphism (SNP) clusters in the National Center for Biotechnology Information (NCBI) Pathogen Detection browser, and out of those, four isolates were assigned SNP clusters that also contained human isolates, all from dogs. The closest human isolate was 29 SNPs from a dog isolate. A total of 36 resistance genes were identified. The three most common resistance genes were oqxAB, fosA, and bla. None of the isolates had carbapenem resistance genes, although one isolate from a goat had mcr-8.1, a colistin resistance gene. Conclusions: To our knowledge, this is the largest collection of sequenced Klebsiella from sick animals ever assembled, and the results found limited relatedness between these isolates and those from humans, despite the diversity of sequenced isolates.
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Genomic analysis of Klebsiella species isolated from clinically ill animals in the U.S. reveals a wide diversity of strains with minimal genetic similarity to human isolates, indicating limited direct transmission between animals and humans.
Study Background and Objectives
Klebsiella spp. are significant pathogens affecting both humans and animals, often harboring antimicrobial resistance (AMR) genes.
The study aimed to:
Determine the prevalence of antimicrobial resistance genes in Klebsiella isolates from clinically ill animals.
Assess the genetic relatedness between Klebsiella isolates from animals and humans.
Sample Collection and Methods
204 Klebsiella isolates were collected during 2019-2020 from various animal species presented to U.S. veterinary hospitals under the FDA’s Veterinary Laboratory Investigation and Response Network antimicrobial resistance monitoring program.
Animal sources included:
Dogs (138 isolates)
Horses (25 isolates)
Cats (17 isolates)
Avian species (6 isolates)
Cows (5 isolates)
Pigs (3 isolates)
Other mammals (10 isolates)
Whole genome sequencing (WGS) and in silico multilocus sequence typing (MLST) were performed to analyze genetic diversity and sequence types.
National Center for Biotechnology Information (NCBI) Pathogen Detection browser was used to identify single nucleotide polymorphism (SNP) clusters indicating genetic relatedness.
Key Findings: Klebsiella Species and Genetic Diversity
Species distribution among 204 isolates:
Klebsiella pneumoniae: 149 isolates (73.0%)
K. quasipneumoniae: 30 isolates (14.7%)
K. variicola: 15 isolates (7.4%)
K. aerogenes: 5 isolates (2.5%)
K. oxytoca: 4 isolates (2.0%)
K. grimontii: 1 isolate (0.5%)
MLST analysis revealed:
88 known sequence types among all isolates, indicating high genetic diversity.
17 isolates had novel allele combinations unassigned to known sequence types.
Genetic Relatedness Between Animal and Human Isolates
45 isolates clustered into 20 distinct SNP clusters.
Only four isolates (all from dogs) belonged to SNP clusters also containing human isolates.
The closest genetic distance between an animal and human isolate was 29 SNPs, suggesting limited direct transmission or recent common ancestry.
Antimicrobial Resistance Genes Identified
A total of 36 different resistance genes were detected across isolates.
The most prevalent resistance genes included:
oqxAB (confers resistance to quinolones)
fosA (confers resistance to fosfomycin)
bla genes (beta-lactamase enzymes that break down beta-lactam antibiotics)
No carbapenem resistance genes were identified in any animal isolates.
One isolate from a goat carried mcr-8.1, a gene conferring resistance to colistin, an antibiotic of last resort.
Conclusions and Implications
This study represents the largest collection of Klebsiella genomes from sick animals to date.
Results demonstrate a highly diverse Klebsiella population in animals with limited overlap and genetic relatedness to human isolates, suggesting that most Klebsiella strains in animals are distinct from those infecting humans.
The limited sharing of SNP clusters between animal and human isolates indicates low likelihood of frequent direct transmission.
While resistance genes are widespread, the absence of carbapenem resistance and rarity of colistin resistance in animal isolates is notable for public health.
These findings provide important baseline genomic data to monitor antimicrobial resistance and potential zoonotic transmission risks involving Klebsiella from animals to humans.
Cite This Article
APA
Martin G, Tyson GH, Guag J, Strain E, Ceric O.
(2025).
Genomic snapshot of Klebsiella spp. isolates from clinically ill animals reveal diverse lineages with limited relatedness to human isolates.
BMC Vet Res, 21(1), 458.
https://doi.org/10.1186/s12917-025-04686-z
Center for Veterinary Medicine, United States Food and Drug Administration, Laurel, MD, USA.
Tyson, Gregory H
Center for Veterinary Medicine, United States Food and Drug Administration, Laurel, MD, USA.
Guag, Jake
Center for Veterinary Medicine, United States Food and Drug Administration, Laurel, MD, USA.
Strain, Errol
Center for Veterinary Medicine, United States Food and Drug Administration, Laurel, MD, USA.
Ceric, Olgica
Center for Veterinary Medicine, United States Food and Drug Administration, Laurel, MD, USA. Olgica.Ceric@fda.hhs.gov.
Veterinary Laboratory Investigation and Response Network (Vet-LIRN), Center for Veterinary Medicine, United States Food and Drug Administration, 8401 Muirkirk Rd, Laurel, MD, 20708, USA. Olgica.Ceric@fda.hhs.gov.
MeSH Terms
Animals
Klebsiella / genetics
Klebsiella / drug effects
Klebsiella / classification
Klebsiella / isolation & purification
Klebsiella Infections / veterinary
Klebsiella Infections / microbiology
Humans
Anti-Bacterial Agents / pharmacology
Dogs
Cattle
Horses
Swine
Drug Resistance, Bacterial / genetics
Cats
Genome, Bacterial
Microbial Sensitivity Tests
Multilocus Sequence Typing
Conflict of Interest Statement
Declarations. Ethics approval and consent to participate: Not applicable-manuscript does not report on or involve the use of any animal or human data or tissue. Consent for publication: (n/a) Author disclaimer: The views expressed in this article are those of the authors and do not necessarily reflect the official policy of the Department of Health and Human Services, the U.S. Food and Drug Administration or the U.S. Government nor do they endorse either the products or companies mentioned. Competing interests: The authors declare no competing interests.
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