Frequency evaluation of genes encoding siderophores and the effects of different concentrations of Fe ions on growth rate of uropathogenic Escherichia coli

Abstract

Background and Objectives: Bacteria need iron for growth and most of them can actively acquire Fe ions using especial iron-chelating proteins which named siderophores. We aimed to determine the frequencies of iucA, iroN and irp2 genes in the uropathogenic Escherichia coli (UPEC) isolates. We also analyzed the effects of siderophore genes beside iron supplements on growth rate of the isolates. Materials and Methods: Totally, 170 E. coli strains were isolated from urinary tract infections and the presence of 3 siderophore genes were analyzed using PCR among them. Three final concentrations of 0.1, 0.5 and 1 mMFe(II) and Fe(III) ions were made in M9 broth medium. Inoculated cultures were incubated at 37°C for 33 hours and bacterial density in the suspension was measured with 1 hour intervals using spectrophotometer. Results: The frequency of iucA, iroN and irp2 genes among 170 UPEC isolates were 29 (17.1%), 52 (30.6%) and 116 (68.2%), respectively. In addition, Our findings showed that Fe(II) supplements had significantly higher promoting effects on UPEC growth rate almost in all of the three applied concentrations (0.1, 0.5 and 1 mM) compared to the control group (P<0.0001). Differences between Fe(III) supplemented groups and the controls were statistically significant when 1 mM concentration was added into the medium (p<0.05). Conclusion: irp2 gene probably plays a major role in the pathogenesis of UPEC strains. Promoting or inhibitory effects of iron on bacterial growth mainly depend on the iron concentration in the culture medium however different siderophores have different potentials for capturing and assimilation of Fe ions by the bacteria, especially inside the host cell.

Keywords

• Escherichia coli
• siderophore
• aerobactin
• sallmochelin
• Yersiniabactin