Membrane damage to Escherichia coli and bactericidal kinetics by the alternative complement pathway of channel catfish

Abstract

1. 1. Increased permeability of cytoplasmic membranes in Escherichia coli was a consequence of alternative complement pathway (ACP) activity of serum of channel catfish, Ictalurus punctatus. Evidence was provided by β-galactosidase activity extracellularly when E. coli was incubated with catfish serum. 2. 2. Lesions were detected on outer membranes of E. coli following exposure to catfish serum. 3. 3. Catfish ACP induced a temporal sequence of pre-killing and killing phases. 4. 4. Loss of cell viability, killing rate and cytoplasmic enzyme release increased with increasing serum concentrations. 5. 5. By incubating E. coli with sera treated to remove complement, both release of cytoplasmic enzyme and bactericidal activity were eliminated. 6. 6. Lethal activity associated with channel catfish ACP against Gram-negative bacteria was functionally comparable to that seen in mammalian and reptilian systems.