Leslie Dybas

Contrasting immune responses mediate Campylobacter jejuni-induced colitis and autoimmunity.

Campylobacter jejuni is a leading cause of foodborne enteritis that has been linked to the autoimmune neuropathy, Guillain Barré syndrome (GBS). C57BL/6 interleukin (IL)-10+/+ and congenic IL-10−/− mice serve as C. jejuni colonization and colitis models, respectively, but a mouse model for GBS is lacking. We demonstrate that IL-10−/− mice infected with a C. jejuni colitogenic human isolate had significantly upregulated type 1 and 17 but not type 2 cytokines in the colon coincident with infiltration of phagocytes, T cells and innate lymphoid cells (ILCs). Both ILC and T cells participated in interferon-γ (IFN-γ), IL-17, and IL-22 upregulation but in a time- and organ-specific manner. T cells were, however, necessary for colitis as mice depleted of Thy-1+ cells were protected while neither Rag1−/− nor IL-10R blocked Rag1−/− mice developed colitis after infection. Depleting IFN-γ, IL-17, or both significantly ameliorated colitis and drove colonic responses toward type 2 cytokine and antibody induction. In contrast, C. jejuni GBS patient strains induced mild colitis associated with blunted type 1/17 but enhanced type 2 responses. Moreover, the type 2 but not type 1/17 antibodies cross-reacted with peripheral nerve gangliosides demonstrating autoimmunity.

The Campylobacter jejuni CiaD effector protein activates MAP kinase signaling pathways and is required for the development of disease.

BackgroundEnteric pathogens utilize a distinct set of proteins to modulate host cell signaling events that promote host cell invasion, induction of the inflammatory response, and intracellular survival. Human infection with Campylobacter jejuni, the causative agent of campylobacteriosis, is characterized by diarrhea containing blood and leukocytes. The clinical presentation of acute disease, which is consistent with cellular invasion, requires the delivery of the Campylobacter invasion antigens (Cia) to the cytosol of host cells via a flagellar Type III Secretion System (T3SS). We identified a novel T3SS effector protein, which we termed CiaD that is exported from the C. jejuni flagellum and delivered to the cytosol of host cells.ResultsWe show that the host cell kinases p38 and Erk 1/2 are activated by CiaD, resulting in the secretion of interleukin-8 (IL-8) from host cells. Additional experiments revealed that CiaD-mediated activation of p38 and Erk 1/2 are required for maximal invasion of host cells by C. jejuni. CiaD contributes to disease, as evidenced by infection of IL-10 knockout mice. Noteworthy is that CiaD contains a Mitogen-activated protein (MAP) kinase-docking site that is found within effector proteins produced by other enteric pathogens. These findings indicate that C. jejuni activates the MAP kinase signaling pathways Erk 1/2 and p38 to promote cellular invasion and the release of the IL-8 pro-inflammatory chemokine.ConclusionsThe identification of a novel T3SS effector protein from C. jejuni significantly expands the knowledge of virulence proteins associated with C. jejuni pathogenesis and provides greater insight into the mechanism utilized by C. jejuni to invade host cells.

Fungicidal activity of anidulafungin in serum from patients does not correlate to its susceptible breakpoint against Candida spp.

A et al. A multicenter trial of the efficacy and safety of tigecycline versus imipenem/cilastatin in patients with complicated intra-abdominal infections. BMC Infect Dis 2005; 5: 88. 2 Ellis-Grosse EJ, Babinchak T, Dartois N et al. The efficacy and safety of tigecycline in the treatment of skin and skin-structure infections: results of 2 double-blind phase 3 comparison studies with vancomycin-aztreonam. 3 Tanaseanu C, Bergallo C, Teglia O et al. Integrated results of 2 phase 3 studies comparing tigecycline and levofloxacin in community-acquired pneumonia. 4 Curcio D. Tigecycline for treating bloodstream infections: a critical analysis of the available evidence. 6 Jenkins I. Linezolid-and vancomycin-resistant Enterococcus faecium endocarditis: successful treatment with tigecycline and daptomycin. 7 Schutt AC, Bohm NM. Multidrug-resistant Enterococcus faecium endocarditis treated with combination tigecycline and high-dose daptomycin. 9 Florescu I, Beuran M, Dimov R et al. Efficacy and safety of tigecycline compared with vancomycin or linezolid for treatment of serious infections with methicillin-resistant Staphylococcus aureus or vancomycin-resistant enterococci: a Phase 3, multicentre, double-blind, randomized study. 10 Cunha BA. Once-daily tigecycline therapy of multidrug-resistant and non-multidrug-resistant Gram-negative bacteraemias. 12 Anthony K, Fishman N, Linkin D et al. Clinical and microbiological outcomes of serious infections with multidrug-resistant Gram-negative organisms treated with tigecycline. A Phase 3, open-label, non-comparative study of tigecycline in the treatment of patients with selected serious infections due to resistant Gram-negative organisms including Enterobacter species, Acinetobacter baumannii and Klebsiella pneumoniae. Use of tigecycline for the treatment of prolonged bacteraemia due to a multiresistant VIM-1 and SHV-12 b-lactamase-producing Klebsiella pneumoniae epidemic clone. Clinical experience of serious infections caused by Enterobacteriaceae producing VIM-1 metallo-b-lactamase in a Greek university hospital. 18 Rolston K, Raad I, Hachem R et al. Tigecycline use in cancer patients with serious infections. A report on 110 cases from a single institution. Fungicidal activity of anidulafungin in serum from patients does not correlate to its susceptible breakpoint against Candida spp. Sir, Echinocandins, such as anidulafungin, are now considered a primary treatment for patients with suspected candidiasis or candidaemia. 1 Common Candida spp. are highly susceptible to these antifungal agents and .99% of isolates are inhibited by 2 mg/L, the current susceptible breakpoint. 2 In vitro time – kill studies find that echinocandins are fungicidal against Candida spp. at concentrations achieved in serum. 3 A major concern with the results from in vitro studies is the absence of testing in the presence of serum proteins. The echinocandins are highly …

Anti-anaerobic activity of serum from patients treated with tigecycline for skin/soft tissue infections.

To gain additional data concerning the anti-anaerobic activity of tigecycline in serum, we analyzed blood samples from six patients with a complicated skin/soft tissue infection who were receiving IV tigecycline 50 mg every 12 h. Venous blood samples were obtained after multiple doses of tigecycline at 1, 6 and 12 h after the initiation of a 1 h IV infusion. Sera from these samples were tested to determine serum inhibitory and bactericidal activity over time against 4 anaerobic bacteria (Bacteroides fragilis, Peptoniphilus asaccharolyticus, Prevotella bivia and Finegoldia magna). An analysis of serum titers found that tigecycline exhibited early (1 h) and prolonged (12 h) inhibitory activity against each study isolate. Moreover, it provided bactericidal activity for 12 h against these strains with the exception of F. magna. Tigecycline was found to exhibit antibacterial activity at serum concentrations below the MICs of the anaerobic bacteria tested. This finding further supports that the antimicrobial activity of tigecycline can be greater than that suggested by the free fraction of drug and that serum appears to enhance this antibacterial activity.

Phenotypic and Genotypic Analyses of Methicillin-Resistant Staphylococcus aureus Isolates from a Community Hospital

Background:Strains of methicillin-resistant Staphylococcus aureus (MRSA) with decreased susceptibility to vancomycin (Van) have become a concern because of the increased risk of clinical failure. Methods:In this study, we obtained all clinical isolates of MRSA cultured over a 1 month period (April 2007) from the microbiology laboratory in a 500-bed community/teaching hospital in Lansing, Michigan. Each isolate was analyzed for Van susceptibility and selected other agents. All isolates with Van minimal inhibitory concentrations (MICs) of 2.0 &mgr;g/mL were further analyzed by transmission electron microscopy for cell wall thickness, polymerase chain reaction for accessory gene regulator (agr) subtypes, and &dgr;-hemolysin expression. Results:We found that 52 (65%) of the 80 strains had Van MICs greater than 1.0 &mgr;g/mL. None were resistant or heteroresistant to Van or other agents tested such as linezolid (MIC90, 1.5 &mgr;g/mL), daptomycin (MIC90, 0.75 &mgr;g/mL), and tigecycline (MIC90, 0.19 &mgr;g/mL). The mean cell wall thickness of 9 strains with Van MICs of 2.0 &mgr;g/mL was similar to an S. aureus American Type Culture Collection (ATCC, no. 29213) strain with a Van MIC of 0.5 &mgr;g/mL. Analysis of the agr subtypes found that 5 isolates (56%) had agr II polymorphism, and all 9 strains had diminished or absent &dgr;-hemolysin expression. Conclusions:Most MRSA strains in this study had Van MICs greater than 1.0 &mgr;g/mL. Those MRSA strains with Van MICs of 2.0 &mgr;g/mL did not have thickened cell walls but had decreased &dgr;-hemolysin expression, which is associated with diminished bactericidal activity of Van.

Serum Bactericidal Activity of Levofloxacin and Moxifloxacin Against Strains of Streptococcus pneumoniae With First-Step Mutations

Background: The increase in minimal inhibitory concentrations (MICs) to fluoroquinolones (FQ) among Streptococcus pneumoniae is of global concern. Strains with first-step mutations have a higher likelihood of subsequent mutations that can lead to complete resistance and clinical failure. Methods: Patients admitted to the hospital with a diagnosis of community-acquired bacterial pneumonia were equally randomized to receive levofloxacin (Levo; 750 mg intravenously for 60 minutes) or moxifloxacin (Moxi; 400 mg intravenously for 60 minutes) once daily for treatment of their infection. After the third dose, blood samples were obtained at the end of the infusion (peak), at 12 hours (midpoint), and before the next dose (trough). The bactericidal activities of Levo and Moxi at each time point were determined by time-kill methodology against S. pneumoniae isolates including those with first-step mutations. Results: Peak concentrations of both Levo and Moxi produced bactericidal activity by 6 hours against a wild-type strain of S. pneumoniae. Against a parC mutation, both FQs exhibited bactericidal activity with the peak and midpoint concentrations. Only Moxi exhibited antibacterial activity with the trough serum concentrations. Against the parE mutant, similar kill curves were observed by the peak and midpoint concentrations for Levo and Moxi. With the trough concentration, Moxi continued to produce bactericidal activity, whereas no inhibition was observed with Levo. Against the gyrA mutants, neither FQ exhibited bactericidal activity. Moxi exhibited greater inhibitory activity than Levo against one of these strains, although regrowth occurred by 24 hours with the midpoint and trough concentrations. We did not detect any changes in the MICs of these study isolates to either of these FQs during our time-kill experiments. Conclusions: Using concentrations achieved in serum with 750 mg of Levo and 400 mg of Moxi, we would expect comparable treatment outcomes for these 2 respiratory FQs against susceptible isolates of S. pneumoniae including those with first-step mutations. Alternative antimicrobial agents should be used to treat S. pneumoniae strains with intermediate susceptibility (Levo MICs > 2 mg/L and Moxi MICs > 0.5 mg/L) to fluoroquinolones.