Inhibition of macrophage phagocytosis by Bacteroides fragilis in vivo and in vitro

Music of metagenomics-a review of its applications, analysis pipeline, and associated tools

This humble effort highlights the intricate details of metagenomics in a simple, poetic, and rhythmic way. The paper enforces the significance of the research area, provides details about major analytical methods, examines the taxonomy and assembly of genomes, emphasizes some tools, and concludes by celebrating the richness of the ecosystem populated by the "metagenome."

Gut Bacteroides species in health and disease

The functional diversity of the mammalian intestinal microbiome far exceeds that of the host organism, and microbial genes contribute substantially to the well-being of the host. However, beneficial gut organisms can also be pathogenic when present in the gut or other locations in the body. Among dominant beneficial bacteria are several species of Bacteroides, which metabolize polysaccharides and oligosaccharides, providing nutrition and vitamins to the host and other intestinal microbial residents. These topics and the specific organismal and molecular interactions that are known to be responsible for the beneficial and detrimental effects of Bacteroides species in humans comprise the focus of this review. The complexity of these interactions will be revealed.

Replication of Colonic Crohn's Disease Mucosal Escherichia coli Isolates within Macrophages and Their Susceptibility to Antibiotics

There is increasing evidence that Escherichia coli organisms are important in Crohn's disease (CD) pathogenesis. In CD tissue they are found within macrophages, and the adherent-invasive CD ileal E. coli isolate LF82 can replicate inside macrophage phagolysosomes. This study investigates replication and antibiotic susceptibility of CD colonic E. coli isolates inside macrophages. Replication of CD colonic E. coli within J774-A1 murine macrophages and human monocyte-derived macrophages (HMDM) was assessed by culture and lysis after gentamicin killing of noninternalized bacteria and verified by electron microscopy (EM). All seven CD colonic isolates tested replicated within J774-A1 macrophages by 3 h (6.36-fold +/- 0.7-fold increase; n = 7 isolates) to a similar extent to CD ileal E. coli LF82 (6.8-fold +/- 0.8-fold) but significantly more than control patient isolates (5.2-fold +/- 0.25-fold; n = 6; P = 0.006) and E. coli K-12 (1.0-fold +/- 0.1-fold; P < 0.0001). Replication of CD E. coli HM605 within HMDM (3.9-fold +/- 0.7-fold) exceeded that for K-12 (1.4-fold +/- 0.2-fold; P = 0.03). EM showed replicating E. coli within macrophage vacuoles. Killing of HM605 within J774-A1 macrophages following a 3-h incubation with antibiotics at published peak serum concentrations (C(max)) was as follows: for ciprofloxacin, 99.5% +/- 0.2%; rifampin, 85.1% +/- 6.6%; tetracycline, 62.8% +/- 6.1%; clarithromycin, 62.1% +/- 5.6% (all P < 0.0001); sulfamethoxazole, 61.3% +/- 7.0% (P = 0.0007); trimethoprim, 56.3% +/- 3.4% (P < 0.0001); and azithromycin, 41.0% +/- 10.5% (P = 0.03). Ampicillin was not effective against intracellular E. coli. Triple antibiotic combinations were assessed at 10% C(max), with ciprofloxacin, tetracycline, and trimethoprim causing 97% +/- 0.0% killing versus 86% +/- 2.0% for ciprofloxacin alone. Colonic mucosa-associated E. coli, particularly CD isolates, replicate within macrophages. Clinical trials are indicated to assess the efficacy of a combination antibiotic therapy targeting intramacrophage E. coli.

Experimental maxillary sinusitis induced by Bacteroides fragilis. A bacteriological and histological study in rabbits

Experimental anaerobic maxillary sinusitis was induced in New Zealand White rabbits by blocking the ostium and inoculating Bacteroides fragilis, strain NCTC 9343. The animals were examined histologically and bacteriologically after 5 days, and 2, 3 and 4 weeks. All the infected sinuses displayed signs of moderate or severe inflammation throughout the study period. Ciliary damage and desquamation, hyperplasia and metaplasia of the epithelium were characteristic features. Furthermore, heavy leukocyte- and, particularly, round cell-infiltration, fibrosis, periosteal hyperplasia and bone degradation and -formation were also frequently encountered. The secretory cell count in the epithelium increased, including the regeneration of goblet cells. After 4 weeks no obvious recovery could be seen, and the inducing microorganism was re-isolated in the majority of cases. In comparison with experimental pneumococcal sinusitis, the B. fragilis infection exerts a more prolonged and severe inflammation.

Suppression of blastogenic transformation of lymphocytes by Bacteroides fragilis in vitro and in vivo

Bacteroides species and Enterobacteriaceae are known to cause synergistic infections. However, the mechanisms behind this synergy are not completely understood. Several authors have shown that Bacteroides species may inhibit the phagocytosis of Enterobacteriaceae by polymorphonuclear leukocytes as well as by macrophages. With the present study we have addressed the question of whether Bacteroides fragilis (BF) is also capable of suppressing specific immune functions. When incubated together with murine lymphocytes, BF significantly inhibited the blastogenic transformation of these cells stimulated by Escherichia coli-lipopolysaccharide (LPS) or concanavalin A. This effect was dose dependent and was not mediated by prostaglandins. Other bacteria such as E. coli or Listeria monocytogenes did not show such an extensive suppression, while Streptococcus pneumoniae was equally active. BF also inhibited the pokeweed mitogen induced blastogenic transformation of human lymphocytes. Moreover, lymphocytes from BF-injected animals obtained 3 to 12 hours after infection proved to be partly refractory for LPS-stimulation. Finally, BF injections also affected T-cell dependent immunity as judged from the aggravation of an experimental listeriosis in mice.

Effects of anti-Bacteroides-antibodies on Escherichia coli and different Bacteroides species in vitro and vivo

Bacteroides species are known to cause synergistic pathogenicity in mixed infections with Enterobacteriaceae. In vitro studies showed that anaerobes may compete with aerobes for opsonisation thus interfering with the phagocytosis and killing of the latter by leukocytes. The present study investigated the effect of anti-Bacteroides-antibodies on in vitro phagocytosis of E. coli and on experimental mixed infections. It was shown that in vitro, B. fragilis suppressed the phagocytosis of E. coli by leukocytes only moderately. The addition of specific antibodies to the phagocytosis mixture could enhance this effect. However, antibodies in the absence of B. fragilis were also active suggesting a nonspecific mechanism such as blockade of Fc receptors. Prophylactic treatment with the immunoglobulin preparations failed to protect mice from experimental infections with E. coli and Bacteroides species.

Induction of an atypical interferon by bacteroides fragilis and Escherichia coli in experimental infections and in leukocyte cultures

Previous reports have shown that Bacteroides fragilis may enhance the pathogenicity of coinfecting enterobacteriaceae by interfering with the host's immune response. With the present study, we have investigated the possible role of interferons (IFN) in mediating these effects. Mice injected with B. fragilis developed moderate serum levels of IFN that appeared just prior to alterations of the animals' immunity described earlier. The IFN was neutralized by treatment with anti-IFN-alpha/beta-antibodies or hydrochloric acid; hence it displayed the same "atypical" characteristics as IFN found in patients with immuno-compromising diseases such as AIDS, systemic lupus erythematosus or rheumatoid arthritis. Escherichia coli displayed the same induction patterns as B. fragilis, while gram-positive bacteria induced "regular" IFN alpha/beta and gamma. Spleen cells, peritoneal macrophages, or liver leukocytes taken from B. fragilis or E. coli-injected animals 6 h post infection were refractory to IFN induction by E. coli lipopolysaccharide in vitro; cells from mice infected with gram-positive organisms showed normal or enhanced responsiveness.