Klebsiella spp. in healthy pigs: reservoirs of antimicrobial resistance and potential pathogenic threats

Abstract Aim The aim of this study was to isolate Klebsiella spp. from clinically healthy animals fed diets with or without antimicrobial growth promoters (AGP). Additionally, the study evaluated whether the inclusion of growth promoters affected the recovery of multi-drug-resistant isolates. Methods and results A total of 144 isolates were obtained from rectal swabs on Simmons citrate agar supplemented with 1% inositol. Of these, 45 non-replicative isolates underwent extensive characterization, including molecular and phenotypic analyses. Sequencing identified that 77% were Klebsiella pneumoniae, 14.5% K. aerogenes, and 8.5% K. variicola. Isolates exhibiting the same polymorphic profiles were detected across different animals and treatments, with and without AGP. Seventy-one percent were multidrug-resistant, as determined by disk diffusion testing. The isolates harbored genes such as mcr-1, blaCTX-M-2, sul2, tetB, qnrS, and dfrA, among others. Additionally, genes encoding siderophores like enterobactin, aerobactin, and yersiniabactin were detected via Polymerase Chain Reaction (PCR). Thirty-nine isolates were strong biofilm producers, 45% moderate, and 16% weak in vitro tests. The predominant genetic profiles included single, double, or triple-locus variants of ST25, ST147, and ST4691. Two novel sequence types were identified: ST7694 (K. pneumoniae) and ST7699 (K. variicola). Survival and persistence analyses in Galleria mellonella showed that these isolates exhibited a virulent phenotype and an enhanced capacity for multiplication in the early hours of infection. Conclusion Clinically healthy swine act as reservoirs for multidrug-resistant Klebsiella spp. exhibiting significant virulence phenotypes. The identification of novel sequence types contributes to epidemiological surveillance and the One Health framework.