Endotoxins and bacterial virulence

Acute cholecystitis associated with infection of Enterobacteriaceae from gut microbiota

Acute cholecystitis (AC) is one of the most common surgical diseases. Bacterial infection accounts for 50% to 85% of the disease's onset. Since there is a close relationship between the biliary system and the gut, the aims of this study were to characterize and determine the influence of gut microbiota on AC, to detect the pathogenic microorganism in the biliary system, and to explore the relationship between the gut and bile microbiota of patients with AC. A total of 185 713 high-quality sequence reads were generated from the faecal samples of 15 patients and 13 healthy controls by 16S rRNA gene pyrosequencing. Patients' samples were significantly enriched in Akkermansia, Enterobacter and Escherichia/Shigella group. The healthy controls, however, showed significant enrichment of Clostridiales, Coprococcus, Coprobacillaceae, Paraprevotella, Turicibacter and TM7-3 in their faecal samples. Escherichia coli was the main biliary pathogenic microorganism, among others such as Klebsiella spp., Clostridium perfringens, Citrobacter freundii and Enterobacter cloacae in the bile of the patients. Additionally, the amount of bile endotoxin significantly correlated with the number of Enterobacteriaceae, especially E. coli. Our data indicate that Enterobacteriaceae might play essential role in the pathogenesis and/or progress of AC. This was verified in an in vivo model using a pathogenic E. coli isolated from one of the patients in guinea pigs and observed marked gallbladder inflammation and morphologic changes. This study thus provides insight which could be useful for the prevention, diagnosis and treatment of AC and related diseases by controlling the growth of Enterobacteriaceae to alleviate the infection.

Elaboration of a 3.6-kilodalton lipooligosaccharide, antibody against which is absent from human sera, is associated with serum resistance of Neisseria gonorrhoeae

Neisseria gonorrhoeae strains that resist lysis by normal human sera (NHS) do so, in part, because NHS contain immunoglobulin M (IgM) specific for lipooligosaccharide (LOS) antigens of serum-sensitive strains, but lack antibodies for LOS antigens that can serve as loci for immune lysis of serum-resistant (serr) strains. We used a monoclonal antibody (McAb), specific for an epitope within a 3.6-kilodalton (kDa) component of Neisseria meningitidis L8 LOS, that binds a 3.6-kDa gonococcal LOS component so that we could explore further serr gonococcal strains. The McAb bound to the LOS of 6 of 7 serr of strains but not to the LOS of 0 of 14 serum-sensitive and serum-intermediate gonococcal strains of diverse origin. We studied three serr strains further. Strain 7134 does not elaborate the 3.6-kDa LOS component and does not bind the McAb; strains WR220 and WR302 do elaborate the 3.6-kDa LOS component. The titer (log2) at which the McAb, diluted in NHS, lysed strain WR220 was 7.7; for WR302 it was 3.7, and for 7134 it was 0. Addition of McAb to NHS caused increased classical and alternative-pathway C3 deposition onto strain WR220, but only classical-pathway-activated C3 deposition onto strain WR302. The difference in lytic effectiveness of the McAb for the two strains, therefore, may result from differences in alternative-pathway augmentation of McAb-dependent classical-pathway activation on their surfaces. None of 40 randomly selected normal young adults had serum antibody that could compete with the McAb for binding to WR220 LOS in a solid-phase RIA. We conclude that the 3.6-kDa LOS component is commonly expressed by serr strains of N. gonorrhoeae and that antibody to it would be lytic if present in human serum, but that it is infrequently, if ever, present. As a result, strains elaborating this LOS are resistant to lysis by NHS.

Phagocytosis and intracellular killing of the contagious equine metritis organism by equine neutrophils in serum

Equine neutrophils were combined with Haemophilus equigenitalis (contagious equine metritis organism; CEMO) or Escherichia coli in low- and high-antibody-titer serum to evaluate the neutrophils ability to phagocytize and kill these bacteria. More E. coli than CEMO were phagocytized at each time period. After 120 min in low-antibody-titer serum, 56.3% of the E. coli and 34.3% of the CEMO were phagocytized. A total of 45% of CEMO and 74.9% of E. coli were phagocytized by 120 min when neutrophils were in high-antibody-titer serum. More than 75% of the ingested E. coli and 90% of the ingested CEMO were killed within 210 min of incubation. Fewer E. coli than CEMO were killed at any given time period. Ultrastructural examination showed CEMO to be degraded in the neutrophil. Degradation was the most extensive in neutrophils in high-titer serum. It is suggested that CEMO is a pathogenic extracellular bacterium incapable of prolonged intracellular survival and that it is slower to be phagocytized than a nonpathogenic E. coli.

Interaction of Mycoplasma hyopneumoniae with the porcine respiratory epithelium as observed by electron microscopy

An in vivo-passaged strain of Mycoplasma hyopneumoniae attained viability titers of 10(6) to 10(8) color-changing units per mg of tissue in pig lungs and caused gross and histological pulmonic lesions. Mycoplasmas were readily located in the lumina of the respiratory tract by electron microscopy. In sections of tissue fixed in glutaraldehyde-osmium, the organisms were found to possess many radial fibrils on the outer surface of the limiting membrane. These fibrils appeared to interconnect adjacent mycoplasmas and to extend between the organism and epithelial cell. Ruthenium red staining demonstrated a thick, dark layer of capsular material enveloping the entire mycoplasma cell. The capsular material was seen to bridge the space between the mycoplasma and host cell. The general morphology of the in vitro-passaged strains grown in broth medium was essentially similar to that of the in vivo-passaged strain. In these organisms, however, no long fibrils were seen, although a fuzzy layer was present outside the cell membrane. The ruthenium red-positive capsule was stained less intensely, and its width was only about one-half that observed for the in vivo-passaged strain. In negatively stained preparations, the cells had an outer fringe of amorphous material apparently corresponding to the fuzzy layer seen in thin sections. The in vitro-passaged strain grew poorly in pig lungs and lost its ability to produce gross pulmonic lesions. The organisms in the respiratory tract had a capsule much thinner than that of the in vivo-passaged strain.

Characterization of opsonins for Bacteroides fragilis in immune sera collected from experimentally infected mice

Serum collected from mice experimentally infected with Bacteroides fragilis 23745 (immune serum) was analyzed for its ability to opsonize the in vitro ingestion of this organism by mouse peritoneal macrophages. B. fragilis was shown to be phagocytized most efficiently in the presence of immune serum although normal mouse serum demonstrated reduced, but significant, opsonic activity. Phagocytosis was greater in the presence of serum collected from animals inoculated twice with the organism than in the presence of serum from once-inoculated animals. The increased opsonic activity of serum from twice-inoculated animals compared to singly inoculated animals was associated with increases in immunoglobulin G1(IgG1), IgG2a, and IgG2b but not IgM. Adsorption analysis of immune serum with homologous or heterologous bacterial antigens indicated that both antibody and complement act synergistically in opsonizing B. fragilis, although either alone may effectively opsonize this organism. Further evaluation of antibody-mediated opsonization revealed that prior treatment of heat-inactivated immune serum with the reducing agent 2-mercaptoethanol caused a slight, but significant, decrease in opsonic activity, thus indicating that IgM is a minor opsonizing antibody for B. fragilis. When ingestion of a B. fragilis stock strain (23745) was compared to a recent clinical isolate (C-1), it was observed that the stock strain was more easily phagocytized in the presence of normal mouse serum, thus suggesting a possible anti-opsonic-phagocytic property of the clinical strain. In addition, the clinical isolate was phagocytized to a significantly greater degree in an aerobic than an anaerobic environment. Subsequent analysis of in vitro killing of B. fragilis 23745 by peritoneal macrophages reflected the previous results in that optimal killing occurred in the presence of immune serum, although normal serum promoted phagocytic killing to an intermediate degree. Thus, these studies implicate both antibody and complement, either alone or in combination, in the opsonization of B. fragilis. Moreover, the virulence of clinical B. fragilis strains may relate to their refractoriness to opsonization and phagocytosis.

Cellular antimicrobial immunity

Acquired resistance to infectious disease may be expressed by a predominantly humoral or a cellular mechanism or, more frequently, by a combination of the two. The cellular interactions which are responsible for the induction of the immune response in the skin, lung, intestinal mucosa, genitourinary tract, conjunctiva, and peritoneal cavity are discussed and the role of living or dead vaccines in the induction of acquired resistance is outlined. The host response involves three different cell types: the phagocytic cell (polymorphs or macrophages), the thymus-dependent (T) lymphocyte, and the thymus-independent (B) lymphocyte-plasma cell line. The normal unstimulated phagocytic cell is capable of killing most nonpathogenic bacteria that gain entry to the tissues. However, the presence of opsonic antibodies and activated macrophages is required to eliminate the pathogenic intracellular parasites. Such immunological activation involves the presence of sensitized T-lymphocytes in the lesion. The cellular response is also characterized by the simultaneous development of a state of delayed-type hypersensitivity (DTH), along with the antimicrobial CMI response. A rising humoral response normally develops subsequently. Killed bacterial cells (except when incorporated into Freund's complete adjuvant) induce the humoral response without the CMI reaction so that such vaccines are not able to fully protect the host against the naturally acquired disease. With the development of cell fractionation methods as well as the identification of distinctive cell surface markers, suspensions of B- and T-cells and macrophages can now be prepared for use in increasingly sophisticated transfer and reconstitution studies. The role of the different cell types in the expression of humoral and cellular immunity has been determined, and the effect of various immunopotentiating and immunosuppressive regimens on the immune system as a whole has been evaluated quantitatively. These studies have led to an appreciation of the role played by suppressor B- and T-cells in the interplay of both humoral and cellular components of the host defense system during the development of immune tolerance, desensitization, anergy, autoimmunity, and the expression of an anamnestic immune response following reinfection.

Gonococci causing disseminated gonococcal infection are resistant to the bactericidal action of normal human sera

The susceptibility of strains of Neisseria gonorrhoeae to the bactericidal action of normal human sera was determined for isolates from patients with disseminated gonococcal infection and uncomplicated gonorrhea. Serum susceptibility was correlated with penicillin susceptibility and auxotype. 38 of 39 strains (97%) of N. gonorrhoeae from Seattle patients with disseminated gonococcal infection were resistant to the complement-dependent bactericidal action of normal human sera. 36 of these were inhibited by less than or equal to mug/ml of penicillin G and required arginine, hypoxanthine, and uracil for growth on chemically defined medium (Arg-Hyx-Ura- auxotype). 12 of 43 isolates from patients with uncomplicated gonorrhea were also of the Arg-Hyx-Ura-auxotype, inhibited by less than or equal to 0.030 mug/ml of penicillin G, and serum resistant. Of the 31 remaining strains of other auxotypes isolated from patients with uncomplicated gonorrhea, 18 (58.1%) were sensitive to normal human sera in titers ranging from 2 to 2,048. The bactericidal action of normal human sera may prevent the dissemination of serum-sensitive gonococci. However, since only a small proportion of individuals infected by serum-resistant strains develop disseminated gonococcal infection, serum resistance appears to be a necessary but not a sufficient virulence factor for dissemination. Host factors such as menstruation and pharyngeal gonococcal infection may favor the dissemination of serum-resistant strains. Since serum-resistant Arg-Hyx-Ura strains are far more frequently isolated from patients with disseminated gonococcal infection than serum-resistant strains of other auxotypes, Arg-Hyx-Ura-strains may possess other virulence factors in addition to serum resistance.