Reversal of the bactericidal reaction of serum by magnesium ion

Effects of serum components on gram-negative bacteria during bactericidal reactions

Biochemical changes which occur in a smooth strain of Escherichia coli were investigated with hyperimmune rabbit serum as a source of antibody and fresh normal guinea pig serum as a source of complement. Ribonucleic acid synthesis, as shown by incorporation of (3)H-uridine, was decreased as early as 5 min, and deoxyribonucleic acid synthesis, shown by incorporation of (3)H-thymidine, was decreased after 15 min of reaction. Incorporation of glycerol-2-(3)H into membrane lipid ceased after 25 to 30 min, probably as a result of functional or physical disruption of the membrane, or both. Permeability control (as indicated by loss of (3)H-uridine-labeled compounds and by decrease in optical density) and protein synthesis were subsequently shown to be affected after 30 min. The metabolic state of the bacteria was found to be important in determining the outcome of the reaction. This was shown by the influence of the type of medium on the reaction. A complex nutrient medium decreased susceptibility as compared with a simple medium. The energy sources glycerol and acetate also decreased susceptibility. It is postulated that the ability of the cell to prevent or repair damage to the cell membrane may be involved. Therefore, metabolic conditions which allow retention of vital processes associated with the cytoplasmic membrane and cell surface will mitigate the bactericidal effect. Such conditions may occur in vivo during bactericidal reactions.

Sensitization of complement-resistant smooth gram-negative bacterial strains

Many gram-negative bacteria are susceptible to the bactericidal action of complement in the presence of specific antibody. As a general rule, rough strains are readily killed, whereas smooth strains are relatively resistant. The results of this study show that the serum sensitivity of smooth gram-negative organisms can be controlled by the environmental conditions imposed by the test system. Smooth organisms which are completely resistant to the bactericidal action of immune serum plus complement in the presence of divalent cations become quite sensitive in a test system containing a relatively high concentration of certain univalent cations; this effect is potentiated by ethylenediaminetetraacetic acid. Since it is generally accepted that the serum resistance of smooth gram-negative organisms is associated with the protection afforded by their thick lipopolysaccharide layer, it is suggested that environmental conditions favoring serum sensitization cause some structural disorganization of the smooth lipopolysaccharide of these cells.

Polyamines can increase resistance of Neisseria gonorrhoeae to mediators of the innate human host defense

Polyamines are biogenic polycationic molecules involved in key cellular functions. Extracellular polyamines found in bodily fluids or laboratory media can be imported by bacteria or bind to negatively charged bacterial surface structures, where they can impair binding of antimicrobials. We hypothesized that the presence of polyamines in fluids that bathe urogenital mucosal surfaces could alter the susceptibility of the sexually transmitted strict human pathogen Neisseria gonorrhoeae to mediators of the innate host defense. Herein we report that polyamines can significantly increase gonococcal resistance to two structurally diverse cationic antimicrobial peptides (polymyxin B and LL-37) but not to antibiotics that exert activity in the cytosol or periplasm (e.g., ciprofloxacin, spectinomycin, or penicillin). The capacity of polyamines to increase gonococcal resistance to cationic antimicrobial peptides was dose dependent, correlated with the degree of cationicity, independent of a polyamine transport system involving the polyamine permeases PotH and PotI, and was reversible. In addition, we found that polyamines increase gonococcal resistance to complement-mediated killing by normal human serum. We propose that polyamines in genital mucosal fluids may enhance gonococcal survival during infection by reducing bacterial susceptibility to host-derived antimicrobials that function in innate host defense.

Killing of Actinobacillus actinomycetemcomitans by human lactoferrin

Actinobacillus actinomycetemcomitans is a fastidious, facultative gram-negative rod associated with endocarditis, certain forms of periodontal disease, and other focal infections. Human neutrophils have demonstrated bactericidal activity against A. actinomycetemcomitans, and much of the oxygen-dependent killing has been attributed to the myeloperoxidase-H2O2-halide system. However, the contribution of other neutrophil components to killing activity is obscure. Lactoferrin, an iron-binding glycoprotein, is a major constituent of neutrophil-specific granules and is also found in mucosal secretions. In this report, we show that human lactoferrin is bactericidal for A. actinomycetemcomitans. Killing activity required an unsaturated (iron- and anion-free) molecule that produced a 2-log decrease in viability within 120 min at 37 degrees C at a concentration of 1.9 microM. Besides exhibiting concentration dependence, killing kinetics were affected by minor variations in temperature and pH. Magnesium, a divalent cation thought to stabilize lipopolysaccharide interactions on the surface of gram-negative organisms, enhanced lactoferrin killing of A. actinomycetemcomitans, while other cations, such as potassium and calcium, had no effect. Our data suggest that lactoferrin contributes to killing of A. actinomycetemcomitans by human neutrophils and that it may also play a significant role in innate secretory defense against this potential periodontopathogen.

Antimicrobial activity of tertiary amine covalently bonded to a polystyrene fiber

Tertiary amine was covalently bonded to a polystyrene fiber and examined for antibacterial activity. The tertiary amine covalently bonded to a polystyrene fiber (TAF) showed a high antimicrobial activity against Escherichia coli. TAF exhibited a stronger antibacterial activity against gram-negative bacteria (E. coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Salmonella typhimurium, and Serratia marcescens) than against gram-positive bacteria (Staphylococcus aureus and Streptococcus faecalis) or Candida albicans. This activity against E. coli was accentuated by 0.1% deoxycholate or 10 mg of actinomycin D per ml, to which E. coli is normally not susceptible. This implies that TAF causes an increase of the bacterial outer membrane permeability. On the other hand, the antimicrobial activity was inhibited by adding Mg2+ or by lowering the pH. This suggest an electrostatic interaction between the bacterial cell wall and TAF. Scanning electron microscopy showed that E. coli cells were initially attached to TAF, with many projections on the cell surface, but then were apparently lysed after contact for 4 h. Taken together, these results imply that bacteria initially interact with TAF by an electrostatic force between the anionic bacterial outer membrane and the cationic tertiary amine residues of TAF and that longer contact with TAF damages the bacterial outer membrane structure and increases its permeability.

Partial characterization and purification of a rabbit granulocyte factor that increases permeability of Escherichia coli

Recently we reported that rapid killing of Escherichia coli by granulocytes or granulocyte fractions is accompanied by an equally rapid and discrete increase in permeability of the microbial envelope (Beckerdite, Mooney, Weiss, Franson, and Elsbach. 1974. J. Exp. Med. 140: 396-409). Most of this permeability-increasing activity (PI) is found in a crude granule preparation. PI is quantitatively recovered in a 23,000-g supernatant fraction (Sup II) after sulfuric acid extraction of granulocyte homogenates prepared in water. PI is nondialyzable, destroyed by pronase and trypsin, stable at 4degreesC for at least 2 mo, and destroyed by heating at 94degreesC. Anionic substances, such as heparin sulfate and isolated E. coli lipopolysaccharide, bind to and inhibit PI. PI has been purified up to 1,000-fold from homogenate in a yield of 50percent by acid extraction and carboxymethyl-Sephadex chromatography. Such purified fractions have bactericidal activity that equals that of disrupted granulocytes and Sup II, are similarly enriched with respect to granule-associated phospholipase, and protease activities. Whereas E. coli, sensitive to PI, binds or inactivates solubilized PI, a resistant strain of Serratia marcescens does not. Binding of PI to sensitive microorganisms seems to be necessary for expression of its biological activity since both the apparent binding to and the biological effect of PI on E. coli are completely blocked by 10-20 mM Mg2+ or Ca2+. Mg2+ or Ca2+ can reverse the effect on E. coli permeability produced by Sup II or the carboxymethyl-Sephadex fraction but not that produced by granulocyte homogenate. The close association of bactericidal, phospholipase A2, and permeability-increasing activities towards several gram-negative bacterial species suggests that they may be related.

Interaction of complement and polymyxin with gram-negative bacteria

The interaction of complement and polymyxin with gram-negative bacteria has been investigated by using three strains of Salmonella typhimurium in an attempt to determine the loci of complement action. It has been shown that the bactericidal activities of complement and polymyxin towards a smooth gram-negative organism are similarly affected by various components of the bactericidal test system. Further, complement and polymyxin have been shown to act synergistically in the bactericidal event. Evidence is presented which suggests that each agent produces lesions in the outer membrane of gram-negative bacteria, allowing lysozyme to interact with its glycopeptide substrate. An attack on the inner cytoplasmic membrane follows, since cell respiration is rapidly inhibited and this membrane becomes sufficiently disorganized to permit massive leakage of beta-galactosidase from the cytoplasm of the target cells.

Protective role of smooth lipopolysaccharide in the serum bactericidal reaction

The mechanism by which smooth lipopolysaccharide (LPS) protects Salmonella typhimurium C5 from the lethal action of specific antibody and complement has been investigated. Tris(hydroxymethyl)aminomethane (Tris) and ethylenediaminetetraacetate (EDTA), which sensitize S. typhimurium C5 to the bactericidal action of immune serum, were shown to cause appreciable structural modification of the smooth LPS associated with these cells. Mg(2+) was shown to reverse the sensitization of C5 by Tris, but this divalent cation was unable to reverse the sensitizing effect of Tris plus EDTA, which, unlike Tris, caused relatively large amounts of O-antigenic components to be released from the C5 cell wall. The possibility that smooth LPS blocks the interaction of activated complement components with receptors on the cell wall is discussed.

Characteristics of complement-dependent release of phospholipid from Escherichia coli

The release of (32)P-labeled bacterial phospholipid from a smooth Escherichia coli by serum components depends on complement activated by antibody. Phospholipid release in excess antibody tends to be proportional to the concentration of complement as does the release of other cellular constituents. Phospholipids are not simply stripped off during cell lysis. Whereas 94% of the total phospholipid freed from E. coli by mechanical lysis sediments at centrifugal forces sufficient to sediment molecules of 10(6) molecular weight, similar centrifugation sediments only 50% of the phospholipid released by antibody-complement. In fact, after mechanical lysis more than 50% of the phospholipid sediments at velocities sufficient to bring down cell envelopes. Although the bulk of the bacterial phospholipid is located in the cell envelopes, isolated (32)P-labeled cell envelopes and phenol-extracted lipopolysaccharide fails to release phospholipids in the presence of antibody-complement. Moreover, ethylenediaminetetraacetic acid, which like antibody-complement causes loss of cellular selective permeability and prepares E. coli cell walls for the action of lysozyme, releases only small amounts of phospholipid from E. coli and these are sedimentable. The most likely mechanism of phospholipid release caused by antibody-complement appears to be the activation directly or indirectly of an enzyme which is present only in the intact cells.

Studies on vaccination against bacillary dysentery. 5. Studies in Erythrocebus patas

In earlier studies in man it has been demonstrated that streptomycin-dependent shigellae, if given orally in 5 sufficiently large doses, confer a very high type-specific protection against bacillary dysentery.In the present study, 2 groups of Erythrocebus patas monkeys were immunized with live streptomycin-dependent Shigella flexneri 2a, and a third group was not vaccinated. One of the vaccinated groups was given streptomycin with each dose of the live vaccine. The animals that received streptomycin with the vaccine were shedding these organisms in their faeces for a significantly longer period than the animals that did not receive streptomycin. A week after the last dose of vaccine, the animals were challenged with virulent Sh. flexneri 2a organisms. All the control animals developed diarrhoea and excreted challenge organisms for an average of 9 days. None of the 9 immunized animals showed pathological changes nor symptoms of dysentery. On average, they excreted challenge organisms for only 2.3 days.Immunological tests confirmed the immunity of the vaccinated animals.This study shows that 3 doses of live oral streptomycin-dependent Shigella vaccine given together with streptomycin are at least as effective as immunization with 5 doses of the same vaccine without streptomycin. Oral application of streptomycin, therefore, seems to have had an enhancing effect on the immunizing property of live oral streptomycin-dependent enteric vaccines.

The serum bactericidal system: ultrastructural changes in Neisseria meningitidis exposed to normal rat serum

Exposure of meningococci to the bactericidal system of normal rat serum initiates a series of ultrastructural changes that accompany death of the organism. These morphological alterations consist of complement-dependent holes in the cell wall outer membrane, edema of the periplasmic space and cytoplasm, and accumulation of fibrillar material in and on the cell wall. Dissolution of the dense line and rupture of the cytoplasmic membrane also occur in meningococci exposed to normal rate serum. These latter two changes, however, are not seen in meningococci that are killed by bentonite-absorbed (lysozyme-deficient) serum, nor are they invariably present when other serum-susceptible organisms (N. catarrhalis and Herellea sp.) are treated with normal rat serum. The pattern of development of edema in serum-treated meningococci suggests that the cell wall outer membrane, mucopeptide layer, and cytoplasmic membrane act synergistically to maintain osmotic equilibrium of the bacterium. Death of the bacterium seems related to alteration of permeability following injury to the outer membrane. Holes are demonstrable, by negative straining, in the outer membrane of the meningococcal cell wall after exposure to the bactericidal effects of rat serum. The lesions are 110 A average greatest diameter and depend on the presence of antibody and complement for their formation. In addition, 82 A diameter holes are present in the walls of normal, untreated meningococci. The relation of complement-dependent holes to the smaller, naturally occurring holes is not known.