A Novel Model of Invasive Fungal Rhinosinusitis in Rats

Overcoming bacteriophage insensitivity in Staphylococcus aureus using clindamycin and azithromycinat subinhibitory concentrations

BACKGROUND

Staphylococcus aureus is a pathogen of major concern in both acute infections and chronic conditions such as chronic rhinosinusitis (CRS). Bacteriophage (phage) therapy has recently regained interest for its potential to treat infections caused by antibiotic resistant strains including Methicillin Resistant Staphylococcus aureus (MRSA). However, bacteria can adapt and become resistant to phages. The aim of this study is to determine the potential for antibiotics to overcome phage resistance.

METHODS

The susceptibility of S. aureus clinical isolates (CIs) to phages J-Sa36, Sa83 and Sa87 alone or in combination with protein synthesis inhibitor (PSI) antibiotics clindamycin, azithromycin and erythromycin was assessed using plaque spot assays, minimum inhibitory concentration (MIC) assays, double layer spot assays and resazurin assays. The safety and efficacy of subinhibitory PSI antibiotics in combination with phage was tested in a Sprague Dawley rat model of sinusitis infected with a phage resistant S. aureus CI.

RESULTS

All three antibiotics at subinhibitory concentrations showed synergy when combined with all 3 phages against S. aureus CIs in planktonic and biofilm form and could sensitize phage-resistant S. aureus to promote phage infection. The combination of topical subinhibitory clindamycin or azithromycin and phage was safe and could eradicate S. aureus sinonasal biofilms in vivo.

CONCLUSION

Subinhibitory concentrations of PSI antibiotics could sensitize phage-resistant S. aureus and MRSA strains to phages in vitro and in vivo. This data supports the potential use of phage-PSI antibiotic combination therapies, in particular for difficult-to-treat infections with phage-resistant S. aureus and MRSA strains.

In Vitro or In Vivo Models, the Next Frontier for Unraveling Interactions between Malassezia spp. and Hosts. How Much Do We Know?

Malassezia is a lipid-dependent genus of yeasts known for being an important part of the skin mycobiota. These yeasts have been associated with the development of skin disorders and cataloged as a causal agent of systemic infections under specific conditions, making them opportunistic pathogens. Little is known about the host-microbe interactions of Malassezia spp., and unraveling this implies the implementation of infection models. In this mini review, we present different models that have been implemented in fungal infections studies with greater attention to Malassezia spp. infections. These models range from in vitro (cell cultures and ex vivo tissue), to in vivo (murine models, rabbits, guinea pigs, insects, nematodes, and amoebas). We additionally highlight the alternative models that reduce the use of mammals as model organisms, which have been gaining importance in the study of fungal host-microbe interactions. This is due to the fact that these systems have been shown to have reliable results, which correlate with those obtained from mammalian models. Examples of alternative models are Caenorhabditis elegans, Drosophila melanogaster, Tenebrio molitor, and Galleria mellonella. These are invertebrates that have been implemented in the study of Malassezia spp. infections in order to identify differences in virulence between Malassezia species.

Characterization of a novel, papain-inducible murine model of eosinophilic rhinosinusitis

BACKGROUND

Eosinophilic chronic rhinosinusitis (ECRS) is a disease characterized by eosinophilic inflammatory infiltrate and a local type 2 cytokine milieu. Current animal models fail to recapitulate many of the innate and adaptive immunologic hallmarks of the disease, thus hindering the development of effective therapeutics. In the present study, mice were exposed intranasally to the cysteine protease papain, which shares functional similarities with parasitic proteases and aeroallergens, to generate a rapidly inducible murine model of eosinophilic rhinosinusitis.

METHODS

C57BL/6 mice were intranasally instilled with 20 μg papain or heat-inactivated papain (HP) on days 0-2 and days 7-10, and then euthanized on day 11. Nasal lavage fluid (NALF) was analyzed to quantify eosinophils and inflammatory cytokine secretion. Sinonasal tissue was sectioned and stained for goblet cells or homogenized to analyze cytokine levels. Serum samples were assayed for immunoglobulin E (IgE) by enzyme-linked immunoassay. Sinonasal mucosal tissue was dissociated and analyzed by flow cytometry.

RESULTS

Compared with HP treatment, papain induced significant eosinophilia in NALF, goblet cell hyperplasia, innate and adaptive immune cell infiltration, type 2 cytokine production, and IgE responses. Flow cytometric analysis of sinonasal tissues revealed significant inflammatory cell infiltration and interleukin-13-producing cell populations.

CONCLUSION

In this study, we demonstrated that the cysteine protease papain induces allergic sinonasal eosinophilic rhinosinusitis and resembles T-helper 2 cell inflammation and innate immune characteristics of ECRS. This model permits further study into the molecular mechanisms underlying ECRS pathology and provides a model system for the evaluation of potential pharmacologic interventions.

Prospective transfrontal sheep model of skull-base reconstruction using vascularized mucosa

BACKGROUND

No high-fidelity animal model exists to examine prospective wound healing following vascularized reconstruction of the skull base. Such a model would require the ability to study the prospective behavior of vascularized mucosal repairs of large dural and arachnoid defects within the intranasal environment. The objective of this study was to therefore develop and validate a novel, in vivo, transfrontal sheep model of cranial base repair using vascularized sinonasal mucosa.

METHODS

Twelve transfrontal craniotomy and 1.5-cm durotomy reconstructions were performed in 60-kg to 70-kg Dorset/Ovis Aries sheep using vascularized mucosa with or without an adjunctive Biodesign™ underlay graft (n = 6 per group). Histologic outcomes were graded (scale, 0 to 4) by a blinded veterinary histopathologist after 7, 14, and 28 days for a range of wound healing parameters.

RESULTS

All sheep tolerated the surgery, which required 148 ± 33 minutes. By day 7, the mucosa was fully adherent with complete partitioning of the sinus and intracranial compartments. Fibroblast infiltration and flap neovascularization scores significantly increased between day 7 (0.3 ± 0.5 and 0.0 ± 0.0) and day 28 (4.0 ± 0.0, p = 0.01 and 2.0 ± 0.8, p = 0.01; respectively), while hemorrhage scores significantly decreased from 2.5 ± 0.6 to 0.0 ± 0.0 (p = 0.01). The inflammatory scores were not significantly different between the heterologous graft and control sides.

CONCLUSION

The described sheep model accurately reflects prospective intranasal wound healing following vascularized mucosal reconstruction of dural defects. This model can be used in future studies to examine novel reconstructive materials, tissue glues, and transmucosal drug delivery to the central nervous system.

Rodent Models of Invasive Aspergillosis due to Aspergillus fumigatus: Still a Long Path toward Standardization

Invasive aspergillosis has been studied in laboratory by the means of plethora of distinct animal models. They were developed to address pathophysiology, therapy, diagnosis, or miscellaneous other concerns associated. However, there are great discrepancies regarding all the experimental variables of animal models, and a thorough focus on them is needed. This systematic review completed a comprehensive bibliographic analysis specifically-based on the technical features of rodent models infected with Aspergillus fumigatus. Out the 800 articles reviewed, it was shown that mice remained the preferred model (85.8% of the referenced reports), above rats (10.8%), and guinea pigs (3.8%). Three quarters of the models involved immunocompromised status, mainly by steroids (44.4%) and/or alkylating drugs (42.9%), but only 27.7% were reported to receive antibiotic prophylaxis to prevent from bacterial infection. Injection of spores (30.0%) and inhalation/deposition into respiratory airways (66.9%) were the most used routes for experimental inoculation. Overall, more than 230 distinct A. fumigatus strains were used in models. Of all the published studies, 18.4% did not mention usage of any diagnostic tool, like histopathology or mycological culture, to control correct implementation of the disease and to measure outcome. In light of these findings, a consensus discussion should be engaged to establish a minimum standardization, although this may not be consistently suitable for addressing all the specific aspects of invasive aspergillosis.

Prognostic Factors for Survival in Patients with Acute Invasive Fungal Rhinosinusitis

Background

Acute invasive fungal rhinosinusitis (AIFR) is an aggressive opportunistic infection with a high mortality rate. There are few reports that demonstrate an improvement in the overall prognosis. Furthermore, definite prognostic factors related to patient survival remain unclear.

Objective

The objective of this study was to evaluate the various clinical factors related to survival of patients with AIFR.

Methods

This is a retrospective case series with patients treated for AIFR between 1997 and 2013. A total of 45 patients with AIFR were enrolled for analysis. We evaluated demographics, clinical characteristics, and disease course.

Results

Mean age of patients was 59.6 years. AIFR developed most commonly in patients with immunocompromised host, such as diabetes (n = 23) or hematologic malignancy (n = 17). There were two main genera of fungus, Aspergillus (n = 30) and Mucor (n = 14). Headache, cranial neuropathy, visual loss, and orbital pain were the most common presenting symptoms. Overall survival was 53%. Underlying hematologic malignancy and diabetes were significantly associated with overall survival, and accompanying severe neutropenia and elevated C-reactive protein (CRP) were also related to poor prognosis. Initial presentation with facial swelling, involvement of nasal septum, or shorter symptom duration was also associated with survival reduction. Multivariate analysis revealed that CRP more than 5.50 mg/dL (Hazard ratio [HR], 9.04; p = 003) was an independent prognostic factor in patients with AIFR.

Conclusions

Overall survival rate remained approximately 50% in patients with AIFR. The prognosis of AIFR is significantly influenced by underlying diseases, accompanying neutropenia, CRP levels, symptom duration, involvement of septum, and the presence of facial swelling. Elevation of CRP, in particular, was an independent predictor of poor outcomes and should be monitored appropriately.

A novel fungus concentration-dependent rat model for acute invasive fungal rhinosinusitis: an experimental study

Background

Acute invasive fungal rhinosinusitis is a lethal infectious process afflicting immunocompromised individuals. Knowledge about this disease is still limited due to the scarcity of animal models designed to study the pathogenesis of this infection. Mast cells are tissue-resident immune cells that participate in a variety of allergic and inflammatory conditions. Limited attention has been given to the role of mast cells in acute invasive fungal rhinosinusitis. Therefore, the objectives of this study were to create a rat model of acute invasive fungal rhinosinusitis based on analyzing the impact of different fungal concentrations on establishing infection, and to observe the changes of mast cells in rats with this disease.

Methods

Sprague–Dawley rats were divided randomly into four groups, three of which were experimental and received different concentrations of Aspergillus fumigatus inoculations, and one was a control group (D). The inoculated Aspergillus fumigatus concentrations were 5 × 10⁷ conidia/ml in group A, 10⁷ conidia/ml in group B, and 10⁶ conidia/ml in group C. Before fungal inoculation, rats were immunosuppressed using cyclophosphamide and cortisone acetate, and had Merocel sponges inserted into the right nares. Hematology and histopathology investigations were then performed.

Results

An acute invasive fungal rhinosinusitis rat model was established successfully with an incidence rate of 90% in group A, 50% in group B and 10% in group C. Aspergillus fumigatus invasion was observed in 20% of the lungs in group A, but was not seen in the remaining groups. In addition, no fungi invaded the orbital tissue, brains, livers, spleens or kidneys of any rat. Compared with the control set, the total number of mast cells in the experimental groups was not significantly increased, but mast cell degranulation, on the other hand, was only found in infected nasal cavities.

Conclusions

This investigation illustrates that various fungal concentrations have different effects on the incidence of acute invasive fungal rhinosinusitis, and it also demonstrates the feasibility of using this model to study the process of fungal rhinosinusoidal invasion. In addition, the results suggest that mast cells may play a role in the protection of sinuses against acute Aspergillus fumigatus infection and in the clearance of established hyphal masses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0713-y) contains supplementary material, which is available to authorized users.