Comparison of iron acquisition mechanisms and growth characteristics of Escherichia coli from bloodstream infection in patients with low and normal iron status
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Sepsis is a systemic inflammatory response to infection which is one of the major public health issues with significant mortality and morbidity. Bloodstream infections are infectious diseases characterised by the presence of actively proliferating microorganisms in the bloodstream. Both bloodstream infections and sepsis are caused by microbes while bacteria are the most common cause. One of the important elements for bacterial growth is iron, and iron is strictly regulated in the body to protect from infections. However, bacteria evolve their own mechanism to scavenge iron from the host. The purpose of this current study is to compare the iron acquisition mechanisms and growth characteristics from the Escherichia coli from bloodstream patients with low and normal iron status. We used BSI isolates (n=61) and commensal strains (n=24). Of 61 BSI isolates, 32 from BSI with low iron status and 29 from BSI with normal iron status from HUNT2 study in Nord-Trøndelag. The growth experiments revealed that there is only a minor difference in growth characteristics between the groups. We found five phylogenetic groups (A, B1, B2, D and F) based on the core genome analysis. The group B2 was more prevalent within all three groups that showed the lowest growth than strains of other phylogenetic groups. The whole genome sequencing analysis found that there was only minor gene difference between low and normal iron strains, but an interesting difference between the strains from BSI patients and commensal strains. The overall study showed that there was no difference between E. coli strains from BSI patients who had had low iron status vs those who had normal iron status. Thus, our study indicated that there might be other specific factors associated with BSI rather than only bacterial growth and iron acquisition gene. The results need to be confirmed by doing further in-depth study in a larger sample size.