In vitro and in vivo effect of immunoglobulin G on the integrity of bacterial membranes

Serum Complement Activation by C4BP-IgM Fusion Protein Can Restore Susceptibility to Antibiotics in Neisseria gonorrhoeae

Neisseria gonorrhoeae is the etiological agent of gonorrhea, the second most common bacterial sexually transmitted infection worldwide. Reproductive sequelae of gonorrhea include infertility, ectopic pregnancy and chronic pelvic pain. Most antibiotics currently in clinical use have been rendered ineffective due to the rapid spread of antimicrobial resistance among gonococci. The developmental pipeline of new antibiotics is sparse and novel therapeutic approaches are urgently needed. Previously, we utilized the ability of N. gonorrhoeae to bind the complement inhibitor C4b-binding protein (C4BP) to evade killing by human complement to design a chimeric protein that linked the two N-terminal gonococcal binding domains of C4BP with the Fc domain of IgM. The resulting molecule, C4BP-IgM, enhanced complement-mediated killing of gonococci. Here we show that C4BP-IgM induced membrane perturbation through complement deposition and membrane attack complex pore insertion facilitates the access of antibiotics to their intracellular targets. Consequently, bacteria become more susceptible to killing by antibiotics. Remarkably, C4BP-IgM restored susceptibility to azithromycin of two azithromycin-resistant clinical gonococcal strains because of overexpression of the MtrC-MtrD-MtrE efflux pump. Our data show that complement activation can potentiate activity of antibiotics and suggest a role for C4BP-IgM as an adjuvant for antibiotic treatment of drug-resistant gonorrhea.

Seventy-Five Years of Research on Protein Binding

This review summarizes evidence that the impact of protein binding of the activity of antibiotics is multifaceted and more complex than indicated by the numerical value of protein binding alone. A plethora of studies has proven that protein binding of antibiotics matters, as the free fraction only is antibacterially active and governs pharmacokinetics. Several studies have indicated that independent from protein binding of immunoglobulin G, albumin, α1-acid-glycoprotein, and pulmonary surfactant acted synergistically with antibacterial agents, thus suggesting that some intrinsic properties of serum proteins may have mediated serum-antibiotic synergisms. It has been demonstrated that IgG and albumin permeabilized Gram-negative and Gram-positive bacteria and facilitated the uptake of poorly penetrating antibiotics. Alpha-1-acid-glycoprotein and pulmonary surfactant also exerted a permeabilizing activity, but proof that this property results in a sensitizing effect is missing. The permeabilizing effect of serum proteins may explain why serum-antibiotic synergisms do not represent a general phenomenon but are limited to specific drug-bug associations only. Although evidence has been generated to support the hypothesis that native serum proteins interact synergistically with antibiotics, systematic and well-controlled studies have to be performed to substantiate this phenomenon. The interactions between serum proteins and bacterial surfaces are driven by physicochemical forces. However, preparative techniques, storage conditions, and incubation methods have a significant impact on the intrinsic activities of these serum proteins affecting serum-antibiotic synergisms, so these techniques have to be standardized; otherwise, contradictory data or even artifacts will be generated.

[Immunoglobulins in the treatment of bacterial meningitis in childhood]

In a prospective, clinical study forty-four children with bacterial meningitis were treated with antibiotics and underwent a special intravenous treatment with 7-S-immunoglobulins. The children's age ranged between two days and thirteen years. Two of the children died. The other forty-two children did not show any signs of neurological deficiencies upon release from the hospital. The apparently improved prognosis, due to the immunoglobulin therapy, was confirmed by a retrospective study of thirty-six patients, that had an unfavorable prognosis of pneumococcal meningitis. All fourteen patients that had acquired pneumococcal meningitis, and had been treated with immunoglobulins, were clinically cured, whereas in comparison, the sixteen patients of the other group exhibited severe sequelae, and two of them died.

Experimental Klebsiella septicemia in mice: treatment with specific antibodies from the rabbit alone and in combination with gentamicin

Using a model of an experimental Klebsiella pneumoniae septicemia in mice, we examined the therapeutic effect of passively administered specific antibacterial antibodies from rabbits. Both specific IgM and IgG antibody proved to be therapeutically effective. However, the effect of IgG was markedly superior to that of IgM with regard both to the degree of protection and the time interval allowing efficient therapy after infection. The effect of IgG was due to a marked enhancement of in vivo phagocytosis, as demonstrated by monitoring bacterial numbers in the liver, spleen, lungs and kidneys. In mice immunocompromised with cyclophosphamide, treatment with IgG still exerted protection against low challenge inocula. When higher inocula were used, treatment with IgG ceased to influence the final mortality rates but delayed the course of the disease for several days by transient reduction of bacterial numbers in the parenchymal organs. In both normal and immunocompromised mice, concomitant treatment with gentamicin resulted in a marked synergistic enhancement of survival.