Extraintestinal pathogenic isolates of Escherichia coli do not possess active IgA₁, IgA₂, sIgA or IgG proteases

Infections outside of the intestinal tract due to pathogenic strains of Escherichia coli result in significant morbidity, mortality and increased healthcare costs. The ability of these strains to cause both mucosal and systemic infections, as well as recurrent infections due to the same (homologous) strain suggests the hypothesis that strains of E. coli that cause infection outside of the intestinal tract possess proteases that are capable of cleaving IgA₁, IgA₂, sIgA or IgG. To test this hypothesis the ability of eight E. coli strains, isolated from sites outside of the urinary tract and 14 homologous and 11 heterologous strains of E. coli that were isolated from women with recurrent UTI, to cleave IgA₁, IgA ₂, sIgA or IgG was evaluated. Our experimental design allowed for detection of cell-associated and secreted immunoglobulin proteases in both log and stationary phase. Surprisingly, none of these 33 human clinical isolates when grown in iron depleted Luria-Bertani medium or human urine were able to degrade the immunoglobulins assessed. Despite previous studies suggesting otherwise, the findings from this study support the concept that strains of E. coli that cause infection outside of the intestinal tract do not possess proteases that cleave the human immunoglobulins IgA₁, IgA ₂, sIgA or IgG.