Pathogens2015, 4(3), 599-605; doi:10.3390/pathogens4030599 (registering DOI) - published 30 July 2015 Show/Hide Abstract
Abstract: Susceptibility testing with the use of surrogate agents is common among clinical microbiology laboratories. One such example is oxacillin and cefoxitin for β-lactams against methicillin-susceptible Staphylococcus aureus (MSSA). This study aimed to assess the surrogate predictive value (SPV) of oxacillin and cefoxitin for the susceptibility of commonly utilized parenteral β-lactams against MSSA as well as to evaluate the concordance between predictive susceptibility testing and the in vivo exposures for ceftriaxone. Broth microdilution MICs were determined for cefazolin, cefoxitin, ceftaroline, ceftriaxone, nafcillin, and oxacillin against a national collection of 1238 MSSA from US hospitals. Pharmacodynamic profiling was utilized to establish a clinical breakpoint for commonly utilized doses of ceftriaxone. Oxacillin had good SPVs for all the β-lactams tested, whereas cefoxitin produced unacceptable major errors for all four agents and thus appears to be an unacceptable susceptibility surrogate. While oxacillin is an adequate surrogate based on the currently defined laboratory criteria, our data also suggest that caution should be exercised when incorporating this testing approach in the clinical setting in view of the fact that the MIC distribution of MSSA coupled with the commonly utilized low doses of ceftriaxone may result in inadequate in vivo exposures against this pathogen.
Abstract: Legionella spp. and Mycobacterium avium complex (MAC) are opportunistic pathogens of public health concern. Hot water systems, including showers, have been identified as a potential source of infection. This paper describes the colonization of Legionella and MAC on the flexible tubing within a model potable shower system, utilizing thermostatic mixing and a flexible shower head. A MAC qPCR method of enumeration was also developed. MAC and Legionella spp. were detected within the biofilm at maximum concentrations of 7.0 × 104 and 2.0 × 103 copies/cm2 PVC tubing respectively. No significant changes were observed between sample of the flexible shower tubing that dried between uses and those that remained filled with water. This suggested the “unhooking” showerheads and allowing them to dry is not an effective method to reduce the risk of Legionella or MACcolonisation.
Abstract: The Candida albicans RHR2 gene, which specifies a glycerol biosynthetic enzyme, is required for biofilm formation in vitro and in vivo. Prior studies indicate that RHR2 is ultimately required for expression of adhesin genes, such as ALS1. In fact, RHR2 is unnecessary for biofilm formation when ALS1 isoverexpressed from an RHR2-independent promoter. Here, we describe two additional biological processes that depend upon RHR2: invasion into an abiotic substrate and pathogenicity in an abdominal infection model. We report here that abiotic substrate invasion occurs concomitantly with biofilm formation, and a screen of transcription factor mutants indicates that biofilm and hyphal formation ability correlates with invasion ability. However, analysis presented here of the rhr2Δ/Δmutant separates biofilm formation and invasion. We found that an rhr2Δ/Δ mutant forms a biofilm upon overexpression of the adhesin gene ALS1 or the transcription factor genes BRG1 or UME6. However, the biofilm-forming strains do not invade the substrate. These results indicate that RHR2 has an adhesin-independent role in substrate invasion, and mathematical modeling argues that RHR2 is required to generate turgor. Previous studies have shown that abdominal infection by C. albicans has two aspects: infection of abdominal organs and persistence in abscesses. We report here that an rhr2Δ/Δmutant is defective in both of these infection phenotypes. We find here that overexpression of ALS1 in the mutant restores infection of organs, but does not improve persistence in abscesses. Therefore, RHR2 has an adhesin-independent role in abdominal infection, just as it does in substrate invasion. This report suggests that RHR2, through glycerol synthesis, coordinates adherence with host- or substrate-interaction activities that enable proliferation of the C. albicans population.
Abstract: IL-17 protects against pathogens by acting on nonhematopoietic cells to induce neutrophil recruitment through upregulation of chemokines and G-CSF. IL-17- and Th17-deficient humans and mice are susceptible to mucosal Candida albicans infections, linked to impaired neutrophil responses. IL-17 production is traditionally associated with CD4+ Th17 cells. However, IL-17 is also expressed during innate responses to facilitate rapid pathogen clearance. Innate IL-17-expressing cells include various lymphocyte-type subsets, including ILC3, NKT, γδ-T and “natural” Th17 (nTh17) cells. Some reports suggest that neutrophils can express IL-17 during fungal infections. Here, we asked whether neutrophils serve as a source of IL-17 during acute oropharyngeal candidiasis (OPC) using an IL-17A fate-tracking reporter mouse. Mice were subjected to OPC for two days, and oral tissue was analyzed by flow cytometry. IL-17A was expressed by γδ-T cells and TCRβ+ natural Th17 (nTh17) cells, as recently reported. Although infiltrating neutrophils were recruited to the tongue following infection, they did not express the IL-17A reporter. Moreover, neutrophil-depleted mice exhibited normal transcription of both Il17a and downstream IL-17-dependent gene targets after Candida challenge. Thus, in acute OPC, neutrophils are not a measurable source of IL-17 production, nor are they necessary to trigger IL-17-dependent gene expression, although they are essential for ultimate pathogen control.
Abstract: The economic impact of non-lethal human and equine West Nile virus (WNV) disease is substantial, since it is the most common presentation of the infection. Experimental infection with virulent WNV strains in the mouse and hamster models frequently results in severe neural infection and moderate to high mortality, both of which are not representative features of most human and equine infections. We have established a rabbit model for investigating pathogenesis and immune response of non-lethal WNV infection. Two species of rabbits, New Zealand White (Oryctolagus cuniculus) and North American cottontail (Sylvilagus sp.), were experimentally infected with virulent WNV and Murray Valley encephalitis virus strains. Infected rabbits exhibited a consistently resistant phenotype, with evidence of low viremia, minimal-absent neural infection, mild-moderate neuropathology, and the lack of mortality, even though productive virus replication occurred in the draining lymph node. The kinetics of anti-WNV neutralizing antibody response was comparable to that commonly seen in infected horses and humans. This may be explained by the early IFNα/β and/or γ response evident in the draining popliteal lymph node. Given this similarity to the human and equine disease, immunocompetent rabbits are, therefore, a valuable animal model for investigating various aspects of non-lethal WNV infections.
Abstract: Thousands of preventable injuries and deaths are annually caused by microbial, chemical and physical hazards from building water systems. Water is processed in buildings before use; this can degrade the quality of the water. Processing steps undertaken on-site in buildings often include conditioning, filtering, storing, heating, cooling, pressure regulation and distribution through fixtures that restrict flow and temperature. Therefore, prevention of disease and injury requires process management. A process management framework for buildings is the hazard analysis and critical control point (HACCP) adaptation of failure mode effects analysis (FMEA). It has been proven effective for building water system management. Validation is proof that hazards have been controlled under operating conditions and may include many kinds of evidence including cultures of building water samples to detect and enumerate potentially pathogenic microorganisms. However, results from culture tests are often inappropriately used because the accuracy and precision are not sufficient to support specifications for control limit or action triggers. A reliable negative screen is based on genus-level Polymerase Chain Reaction (PCR) for Legionella in building water systems; however, building water samples with positive results from this test require further analysis by culture methods.