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      Toll-Like Receptor-4 Dependent Inflammatory Responses Following Intestinal Colonization of Secondary Abiotic IL10-Deficient Mice with Multidrug-Resistant Pseudomonas Aeruginosa

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          The rising incidences of infections with multidrug-resistant (MDR) Gram-negative bacteria including Pseudomonas aeruginosa (PA) have gained increasing attention in medicine, but also in the general public and global health politics. The mechanisms underlying opportunistic pathogen–host interactions are unclear, however. To address this, we challenged secondary abiotic IL10 –/– mice deficient for Toll-like receptor-4 (TLR4 –/– × IL10 –/–), the main receptor of the Gram-negative cell wall constituent lipopolysaccharide, with a clinical MDR PA isolate. Despite higher intestinal colonization densities, apoptotic colonic epithelial cell numbers were lower in TLR4 –/– × IL10 –/– mice as compared to IL10 –/– controls at day 14 postinfection (p.i.), whereas proliferating/regenerating cells had increased in the latter only. Furthermore, PA-colonized TLR4 –/– × IL10 –/– mice displayed less distinct innate and adaptive immune cell responses in the colon as compared to IL10 –/– counterparts that were accompanied by lower nitric oxide concentrations in mesenteric lymph nodes in the former at day 14 p.i. Conversely, splenic NO levels were higher in both naive and PA-colonized TLR4-deficient IL10 –/– mice versus IL10 –/– controls. Remarkably, intestinal MDR PA was able to translocate to extra-intestinal including systemic compartments of TLR4 –/– × IL10 –/– mice only. Hence, MDR PA-induced intestinal and systemic immune responses observed in secondary abiotic IL10 –/– mice are TLR4-dependent.

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          Most cited references 41

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          Establishment of Pseudomonas aeruginosa infection: lessons from a versatile opportunist.

          Pseudomonas aeruginosa is an ubiquitous pathogen capable of infecting virtually all tissues. A large variety of virulence factors contribute to its importance in burn wounds, lung infection and eye infection. Prominent factors include pili, flagella, lipopolysaccharide, proteases, quorum sensing, exotoxin A and exoenzymes secreted by the type III secretion system.
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            Gram-negative bacteria aggravate murine small intestinal Th1-type immunopathology following oral infection with Toxoplasma gondii.

            Oral infection of susceptible mice with Toxoplasma gondii results in Th1-type immunopathology in the ileum. We investigated gut flora changes during ileitis and determined contributions of gut bacteria to intestinal inflammation. Analysis of the intestinal microflora revealed that ileitis was accompanied by increasing bacterial load, decreasing species diversity, and bacterial translocation. Gram-negative bacteria identified as Escherichia coli and Bacteroides/Prevotella spp. accumulated in inflamed ileum at high concentrations. Prophylactic or therapeutic administration of ciprofloxacin and/or metronidazole ameliorated ileal immunopathology and reduced intestinal NO and IFN-gamma levels. Most strikingly, gnotobiotic mice in which cultivable gut bacteria were removed by quintuple antibiotic treatment did not develop ileitis after Toxoplasma gondii infection. A reduction in total numbers of lymphocytes was observed in the lamina propria of specific pathogen-free (SPF), but not gnotobiotic, mice upon development of ileitis. Relative numbers of CD4(+) T cells did not differ in naive vs infected gnotobiotic or SPF mice, but infected SPF mice showed a significant increase in the frequencies of activated CD4(+) T cells compared with gnotobiotic mice. Furthermore, recolonization with total gut flora, E. coli, or Bacteroides/Prevotella spp., but not Lactobacillus johnsonii, induced immunopathology in gnotobiotic mice. Animals recolonized with E. coli and/or total gut flora, but not L. johnsonii, showed elevated ileal NO and/or IFN-gamma levels. In conclusion, Gram-negative bacteria, i.e., E. coli, aggravate pathogen-induced intestinal Th1-type immunopathology. Thus, pathogen-induced acute ileitis may prove useful to study bacteria-host interactions in small intestinal inflammation and to test novel therapies based on modulation of gut flora.
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              Has the era of untreatable infections arrived?

              Antibiotic resistance is a major public health concern, with fears expressed that we shortly will run out of antibiotics. In reality, the picture is more mixed, improving against some pathogens but worsening against others. Against methicillin-resistant Staphylococcus aureus (MRSA)--the highest profile pathogen--the range of treatment options is expanding, with daptomycin, linezolid and tigecycline all launched, and telavancin, ceftobiprole, ceftaroline and dalbavancin anticipated. There is a greater problem with enterococci, especially if, as in endocarditis, bactericidal activity is needed and the isolate has high-level aminoglycoside resistance; nevertheless, daptomycin, telavancin and razupenem all offer cidal potential. Against Enterobacteriaceae, the rapid and disturbing spread of extended-spectrum beta-lactamases, AmpC enzymes and quinolone resistance is forcing increased reliance on carbapenems, with resistance to these slowly accumulating via the spread of metallo-, KPC and OXA-48 beta-lactamases. Future options overcoming some of these mechanisms include various novel beta-lactamase-inhibitor combinations, but none of these overcomes all the carbapenemase types now circulating. Multiresistance that includes carbapenems is much commoner in non-fermenters than in the Enterobacteriaceae, depending mostly on OXA carbapenemases in Acinetobacter baumannii and on combinations of chromosomal mutation in Pseudomonas aeruginosa. No agent in advanced development has much to offer here, though there is interest in modified, less-toxic, polymyxin derivatives and in the siderophore monobactam BAL30072, which has impressive activity against A. baumannii and members of the Burkholderia cepacia complex. A final and surprising problem is Neisseria gonorrhoeae, where each good oral agent has been eroded in turn and where there is now little in reserve behind the oral oxyimino cephalosporins, to which low-level resistance is emerging.

                Author and article information

                Eur J Microbiol Immunol (Bp)
                Eur J Microbiol Immunol (Bp)
                European Journal of Microbiology & Immunology
                Akadémiai Kiadó (Budapest )
                11 September 2017
                September 2017
                : 7
                : 3
                : 210-219
                Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health , Department of Microbiology and Hygiene, Berlin, Germany
                Author notes
                * Department of Microbiology and Hygiene, Charité – University Medicine Berlin, CC5, Campus Benjamin Franklin, FEM, Garystr. 5, D-14195 Berlin, Germany; +49-30-450524318; markus.heimesaat@
                © 2017, The Author(s)

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium for non-commercial purposes, provided the original author and source are credited, a link to the CC License is provided, and changes – if any – are indicated.

                Page count
                Figures: 6, Tables: 0, Equations: 0, References: 38, Pages: 10
                Original Article


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