Virulence-associated acquisition of iron in mammalian serum by Escherichia coli

Area of Science:

• Microbiology
• Immunology
• Infectious Diseases

Background:

• Iron is essential for bacterial growth, but its availability is limited in host environments.
• Escherichia coli (E. coli) exists in virulent and avirulent forms, with differing pathogenic potentials.
• Host defenses often involve iron sequestration to inhibit bacterial proliferation.

Purpose of the Study:

• To investigate the role of iron in the pathogenicity of virulent and avirulent strains of Escherichia coli.
• To determine how iron availability affects E. coli survival and growth in mammalian sera and in vivo.
• To elucidate the mechanisms by which virulent E. coli overcomes iron-restricted environments.

Main Methods:

• Experiments were conducted using mice models and in vitro cultures with mammalian sera.
• Mortality rates were assessed in mice infected with E. coli strains under varying iron conditions.
• Bacterial growth and survival were monitored in vitro in iron-deprived and iron-supplemented sera, milk, and egg white.
• The role of enterochelin and lipopolysaccharide in iron acquisition was examined.

Main Results:

• Iron administration increased mortality in mice infected with avirulent E. coli to levels comparable to virulent strains.
• In vitro, E. coli deprived of iron ceased multiplication and died rapidly in bovine/human sera, milk, and egg white.
• Antibacterial effects of iron deprivation were reversed by adding exogenous iron or enterochelin.
• Virulent E. coli strains, unlike avirulent ones, successfully acquired iron from mammalian serum and multiplied.

Conclusions:

• Iron availability significantly influences the pathogenicity of E. coli, particularly affecting avirulent strains in vivo.
• Virulent E. coli possesses enhanced mechanisms, including enterochelin and lipopolysaccharide, for iron acquisition from host environments.
• These iron-acquisition strategies are crucial for the survival and proliferation of virulent E. coli in mammalian sera, contributing to disease progression.