Prevalence and immune modulator role of the peg344 gene among hypervirulent Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae (hvKp) is an emerging pathogen threatening healthy and immunocompromised patients. Since hvKp first appeared in Taiwan in 1986, its prevalence has increased drastically around the globe. Yet, there is no study focusing on hypervirulent strains in Turkey. peg344, iutA, and iroB are the highly accurate biomarker genes for hypervirulence. However, the pathogenesis mechanism of the peg344 putative metabolite transporter is still unclear. This study aims to elucidate the hypervirulence surveillance in Turkey and to understand the immune modulator role of the peg344 gene in vivo and in vitro infection models. In total, 230 K.pneumoniae isolates isolated from ten different healthcare centers in Turkey between January 2015 to March 2023 were included in the study. All strains were screened for hypervirulence genes peg344, iutA, and rmpA. The isolates harboring at least two of the hypervirulence gene were categorized as hypervirulence gene K.pneumoniae. The isolates which exhibited a hypermucoviscous phenotype in string test or virulent phenotype in 48-hour C.elegans fertility assay were classified as hypervirulent. The hypervirulence prevalence between 2022-2023 was significantly higher than 2017-2018 (p=0.024), and 2015-2016 (p<0.0001). The most prominent ST types were ST2096, and ST23 (30.77% and 23.08% respectively); K1 and K2 were the most common capsule serotypes among the hypervirulent cohort (46.15% and 15.38% respectively). THP-1-driven macrophage cells were infected with selected isolates including cKp, hgKp, hvKp, and Δpeg344-mutant isolates. hvKp isolates had decreased the viability of macrophages (from 91.5% to 81.5%) and increased the M2 convergence ratio at 2 hours of infection. Macrophages could inhibit the cKp isolates, but hvKp isolates were able to grow inside the macrophages at 3 hours of infection. Also, hvKp infection secreted less TNFα than cKp infection (368, 1462 pg/mL respectively). The peg344 deletion decreased the bacterial growth (from 430% to -3%) within the macrophages and recovered the TNFα secretion levels (from 203 to 824 pg/mL). In conclusion, hypervirulent K.pneumoniae is an emerging pathogen, and a serious concern in our region just like in other parts of the world. The peg344 gene is an accurate biomarker for differentiation in this region. The hypophagia of macrophages and the suppressed proinflammatory responses in the early stages contribute to the severe infections caused by hypervirulent clones. The peg344 gene plays an important role in bacteria's resistance against phagocytosis by macrophage cells.