Reactivity and protective capacity of a polyclonal antiserum derived from mice immunized with antibiotic exposed Escherichia coli

Abstract
The murine immune response to Escherichia coli O6: K — alone or pre-exposed to 0·1 × MIC of aztreonam was investigated. Relative to mice immunized with untreated bacteria, mice immunized with antibiotic-treated microorganisms presented a significantly enhanced protection towards a challenge of 100 × LD50 of viable E. coli O6:K—. Previous injection of 0·1 mL of serum drawn from mice immunized with treated and untreated bacteria protected non-immunized mice towards a challenge of 10 × LD50 of viable E. coli O6: K—. Serum from mice immunized with treated bacteria also protected non-immunized mice towards a lethal challenge of E. coli O111. The antiserum contained high titre of IgG antibodies that cross-reacted with lipopolysaccharide isolated from smooth and rough Gram-negative bacteria. Immunoblotting showed additional bands of reactivity to the untreated E. coli O6: K—. Immunization with antibiotic-treated bacteria led to the production of type specific and cross reactive antibodies that protected animals against viable homologous and heterologous lethal challenges.

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