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Kinetics of the Transformation of Gram-Negative Rods to Spheroplasts and Ghosts by Serum¹

From the Department of Pediatrics, University of Washington School of Medicine, Seattle, Washington

Abstract

Kinetic analysis of the action of serum on Escherichia coli demonstrated that bacterial rods were quantitatively converted to spheroplasts and then to ghosts. The bactericidal action of serum preceded the conversion of rods to spheroplasts by lysozyme. The bacteriolytic action of serum, defined as a decrease in optical density (O.D), was associated with the conversion of spheroplasts to ghosts. These appeared to be consecutive first order reactions. Hypertonic sucrose decreased the rate of both reactions and did not specifically stabilize spheroplasts. Added calcium and magnesium stabilized spheroplasts but did not inhibit bactericidal action or the conversion of rods to spheroplasts.

On the basis of current evidence, bacterial rods are thought to be killed by antibody and complement and converted to spheroplasts by lysozyme. The subsequent conversion of spheroplasts to ghosts may be the result of instability of the exposed cell surface, not a direct effect of serum action.

Studies of antibody-complement action of serum on bacteria based solely on changes in O.D. may be subject to significant errors of interpretation. Investigations of the hemolytic complement system may be subject to similar errors.

Footnotes

¹ This investigation was carried out under the sponsorship of the Commission on Immunization of the Armed Forces Epidemiology Board and was supported in part by the Office of the Surgeon General, Department of the Army (Contract DA-49-193-MD-2308), by the Pediatric Microbiology Training Grant 5 T1 A1-227-03, U.S. Public Health Service, and State of Washington Initiative 171 Funds for Research in Biology and Medicine.

² This work was done during the tenure of a Special Fellowship (5 Fc HD-16,082-02) of the National Institute of Child Health and Human Development.