Global gene expression profiling of a virulent Klebsiella pneumoniae strain during pulmonary infection

Klebsiella pneumoniae (Kpn) is an important respiratory pathogen associated with significant mortality, fierce inflammatory responses and high rates of antimicrobial resistance. The increasing incidence of multidrug resistant Kpn has significantly narrowed the therapeutic options available; as such, there is an urgent need to better understand Kpn pathophysiology to identify novel therapeutic targets. Here we performed an in vivo transcriptomic analysis of Kpn isolated from a mammalian host with pulmonary infection.

C57BL/6 mice were intranasally inoculated with the virulent Kp52.145 strain (serotype O1:K2); with lungs extracted, homogenised and pooled (n=3; in duplicate) at 32 h post-infection for bacterial RNA purification and RNA-Seq (Illumina). Differential gene expression (analysed using Degust [Voom/Limma]; FDR cut-off =0.01, abs log-FC=2) was assessed in comparison with mid-log phase growth in Lennox broth.

Overall, we identified >900 differentially expressed genes (DEGs), comprising ∼17 % of the combined chromosomal and plasmid coding sequence repertoire. 52 % of the DEGs were upregulated during infection, including several siderophore-independent iron-, manganese- and zinc-uptake systems (e.g. hmuRSTUV, sitABCD, mntH and znuACB). We also observed a marked in vivo oxidative stress signal, with several Kpn oxidative stress response genes (e.g. oxyR, katE, katG) upregulated during infection. In contrast, expression of mgrB, a negative-regulator of the PhoPQ two-component system associated with resistance to host antimicrobial peptides was downregulated.

This study provides a novel insight into Kpn gene expression during pulmonary infection. Overall, our data suggest that adaptation to metal starvation, oxidative stress and innate immune defenses are critical for the success of Kpn lung infection.