Sensitivity of Shigella strains to the bactericidal activity of human serum. III. The diversity of activity variants of bactericidal serum factors against Shigella flexneri serotypes.

Normal human serum is bactericidal for all studied Shigella flexneri strains (38) belonging to nine serotypes. Six variants of bactericidal activity of serum factors for these bacteria were determined.     

Sensitivity of Shigella strains to bactericidal activity of human serum. I. Participation of two independently active mechanisms in bactericidal action against Shigella sonnei phase II.

Normal human serum is strongly bactericidal for all studied Shigella sonnei phase II (10 strains). The studied bacteria were sensitive to two alternative mechanisms of the bactericidal activity of serum factors. The first mechanism involves the action of serum in which complement (C) is activated by the studied bacteria via the classical pathway. Lysozyme did not participate in this reaction. The second mechanism involves the combined action of two factors: C activated via the alternative pathway and lysozyme.     

Differential susceptibility to human serum byAeromonas spp.

A total of 91 strains ofAeromonas (A. hydrophila, A. sobria, andA. caviae) of clinical origin were challenged in vitro against pooled human serum. A majority of the isolates ofA. hydrophila andA. sobria were resistant to the bactericidal activity of human serum, as opposed to the more serum-sensitiveA. caviae species. This difference in serum sensitivity may potentially explain the greater association of the former species with bacteremia and invasive disease.     

Sensitivity of Shigella strains to the bactericidal activity of human serum. II. Shigella flexneri 3 a is killed by complement activated via the classical pathway, with participation of lysozyme.

Normal human serum is bactericidal for all studied strains (15) of Shigella flexneri serotype 3a. The activity of the serum was similar irrespective of the invasiveness of the bacteria or its lack. The studied bacteria were susceptible to a single mechanism of bactericidal activity involving complement activated via the classical pathway, accompanied by the action of lysozyme.     

Aerobactin genes in Shigella spp.

Aerobactin, a hydroxamate iron transport compound, is synthesized by some, but not all, Shigella species. Conjugation and hybridization studies indicated that the genes for the synthesis and transport of aerobactin are linked and are found on the chromosome of Shigella flexneri, S. boydii, and S. sonnei. The genes were not found in S. dysenteriae. A number of aerobactin synthesis mutants and transport mutants have been isolated. The most common mutations are deletions of the biosynthesis or biosynthesis and transport genes. The Shigella aerobactin genes share considerable homology with the E. coli ColV aerobactin genes. On the ColV plasmid and in the Shigella chromosome, the aerobactin genes are associated with a repetitive sequence which has been identified as IS1.     

Evaluation of the inhibitory effects of human serum components on bactericidal activity of human beta defensin 3

Naturally occurring cationic antimicrobial peptides (CAPs) are an essential component of the innate immune system of multicellular organisms. At concentrations generally higher than those found in vivo, most CAPs exhibit strong antibacterial properties in vitro, but their activity may be inhibited by body fluids, a fact that could limit their future use as antimicrobial and/or immunomodulatory agents. In the present study, we evaluated the effects of human serum components on bactericidal activity of the human beta-defensin 3 (hBD-3), a CAP considered particularly promising for future therapeutic employment. Human serum diluted to 20% strongly inhibited the bactericidal activity of the peptide against both the Gram-positive species Staphylococcus aureus and the Gram-negative species Acinetobacter baumannii. Such activity was not restored in serum devoid of salts (dialyzed), pre-treated with protease inhibitors, or subjected to both of these treatments. The addition of physiological concentrations of NaCl, CaCl2, and human albumin in the bactericidal assay abolished bactericidal activity of hBD-3 against S. aureus, while it only partially inhibited the activity of the peptide against A. baumannii. Although a proteolytic activity of serum on hBD-3 was demonstrated at the protein level by Western blot, addition of physiological concentrations of trypsin to the bactericidal assay only partially affected the antibacterial properties of the peptide. Altogether, these results demonstrate a major role of mono-divalent cations and serum proteins on inhibition of hBD-3 antibacterial properties and indicate a relative lack in sensitivity of the bactericidal activity of this peptide to trypsin and trypsin-like proteases.     

Influence of ozone on the susceptibility ofEscherichia coli K1 to the bactericidal action of serum

The susceptibility to the bactericidal action of normal bovine serum of twenty twoEscherichia coli K1 strains, isolated from the urine of patients with urinary tract infections, was determined. Only four strains were resistant. Ozonization of bacterial suspensions enhanced the sensitivity of the strains to the action of both normal serum and a serum in which the alternative pathway of complement activation was thermally blocked.     

Suppression of human PMN bactericidal activity by human IgA paraproteins.

IgA paraproteins which have previously been shown to suppress neutrophil chemotaxis were found to suppress neutrophil bactericidal activity in a concentration dependent manner. This inhibition was cell directed, dependent on the Fc portion of the IgA, and lost after reduction and alkylation which resulted in conversion of polymeric to monomeric IgA. IgA suppression of bactericial activity was not due to interference with cell metabolism or membrane fluidity as evidenced by a lack of effect on chemiluminescence or Con-A cap formation. Further tests demonstrated that the presence of IgA paraproteins inhibited PMN ingestion of IgG coated latex particles which could account for their effect on PMN bactericidal activity.     

Francisella tularensis resistance to bactericidal action of normal human serum

Abstract Lipopolysaccharide and outer membranes from the three virulent encapsulated (Cap⁺) strains of three subspecies of Francisella tularensis and their isogenic avirulent capsule-deficient (Cap⁻) mutants were isolated. It was shown that the Cap⁻ cells and their outer membranes almost completely consumed the available complement of normal human serum whereas Cap⁻ LPS (R-LPS), Cap⁺ cells and their components activated the complement less effectively. Absorption of normal human serum with Cap⁻ strain dramatically reduced the complement consumption for homologous strain and its surface structures. This reduction reflected the loss of bactericidal antibodies. Addition of antibodies to whole cells of F. tularensis completely restored complement activity. The cross-absorbing experiments demonstrated that Cap⁻ cells more effectively deplete bactericidal antibodies than homologous virulent strain. From these results it can be concluded that normal human serum is bactericidal for serum-sensitive Cap⁻ F. tularensis strains through the action of complement initiated by the classical complement pathway and serum resistance of virulent strains is not due to absence of targets for bactericidal antibodies, but is due to their low accessibility because of O-side chains of lipopolysaccharide.     

Influence of plasmids on bacterial susceptibility to the bactericidal activity of sera. II. Relation between transfer frequency of R plasmids and their protective activity to the lethal effect of normal rabbit serum

The plasmid pAM-Ia separated from the aggregate R588 protected E. coli K12 cells from the bactericidal action of normal rabbit serum much stronger when carried alone than in the aggregate. When aggregated with R100.1, its protective effect was also weakened. These decreases in protective effect are correlated qualitatively with inhibition of conjugational fertility. On the other hand the plasmid aggregate causing increase in protective activity showed no influence on their fertility.     

志贺菌毒力检测的常用方法

志贺菌属的细菌以人类为特异性宿主,感染人类肠上皮细胞,多导致痉挛性腹痛、腹泻、发烧等症状,是细菌性痢疾最为常见的病原菌。志贺菌的致病机理主要由其Ⅲ型分泌系统调节。志贺菌侵袭力的高低及毒力强弱决定了其致病性的强弱。我们简要介绍志贺菌属细菌的毒力检测方法。