Guinea pig model for Staphylococcus aureus native valve endocarditis

Animal and Human Tissue Models of Vertical Listeria monocytogenes Transmission and Implications for Other Pregnancy-Associated Infections

Intrauterine infections lead to serious complications for mother and fetus, including preterm birth, maternal and fetal death, and neurological sequelae in the surviving offspring. Improving maternal and child heath is a global priority. Yet, the development of strategies to prevent and treat pregnancy-related diseases has lagged behind progress made in other medical fields. One of the challenges is finding tractable model systems that replicate the human maternal-fetal interface. Animal models offer the ability to study pathogenesis and host defenses in vivo However, the anatomy of the maternal-fetal interface is highly divergent across species. While many tools are available to study host responses in the pregnant mouse model, other animals have placentas that are more similar to that of humans. Here we describe new developments in animal and human tissue models to investigate the pathogenesis of listeriosis at the maternal-fetal interface. We highlight gaps in existing knowledge and make recommendations on how they can be filled.

Role of B cells in host defense against primary Coxiella burnetii infection

Despite Coxiella burnetii being an obligate intracellular bacterial pathogen, our recent study demonstrated that B cells play a critical role in vaccine-induced immunity to C. burnetii infection by producing protective antibodies. However, the role of B cells in host defense against primary C. burnetii infection remains unclear. In this study, we investigated whether B cells play an important role in host defense against primary C. burnetii infection. The results showed that peritoneal B cells were able to phagocytose virulent C. burnetii bacteria and form Coxiella-containing vacuoles (CCVs) and that C. burnetii can infect and replicate in peritoneal B1a subset B cells in vitro, demonstrating a potential role for peritoneal B cells in host defense against C. burnetii infection in vivo. In addition, the results showing that B1a cells secreted a high level of interleukin-10 (IL-10) in response to C. burnetii infection in vitro suggest that B1a cells may play an important role in inhibiting the C. burnetii infection-induced inflammatory response. The observation that adoptive transfer of peritoneal B cells did not significantly affect the severity of C. burnetii infection-induced diseases in both severe combined immunity-deficient (SCID) and μMT mice indicates that peritoneal B cells alone may not be able to control C. burnetii infection. In contrast, our finding that C. burnetii infection induced more-severe splenomegaly and a higher bacterial burden in the spleens of B1a cell-deficient Bruton's tyrosine kinase x-linked immunity-deficient (BTK(xid)) mice than in their wild-type counterparts further suggests that B1a cells play an important role in host defense against primary C. burnetii infection.

Protein A suppresses immune responses during Staphylococcus aureus bloodstream infection in guinea pigs

Staphylococcus aureus infection is not associated with the development of protective immunity, and disease relapses occur frequently. We hypothesize that protein A, a factor that binds immunoglobulin Fcγ and cross-links V(H)3 clan B cell receptors (IgM), is the staphylococcal determinant for host immune suppression. To test this, vertebrate IgM was examined for protein A cross-linking. High V(H)3 binding activity occurred with human and guinea immunoglobulin, whereas mouse and rabbit immunoglobulins displayed little and no binding, respectively. Establishing a guinea pig model of S. aureus bloodstream infection, we show that protein A functions as a virulence determinant and suppresses host B cell responses. Immunization with SpA(KKAA), which cannot bind immunoglobulin, elicits neutralizing antibodies that enable guinea pigs to develop protective immunity.

IMPORTANCE

Staphylococcus aureus is the leading cause of soft tissue and bloodstream infections; however, a vaccine with clinical efficacy is not available. Using mice to model staphylococcal infection, earlier work identified protective antigens; however, corresponding human clinical trials did not reach their endpoints. We show that B cell receptor (IgM) cross-linking by protein A is an important immune evasion strategy of S. aureus that can be monitored in a guinea pig model of bloodstream infection. Further, immunization with nontoxigenic protein A enables infected guinea pigs to elicit antibody responses that are protective against S. aureus. Thus, the guinea pig model may support preclinical development of staphylococcal vaccines.

Right atrial pressure alterations during echocardiography-guided-catheterization predict tricuspid valvular impairment: a novel method for the creation of a rabbit model of Staphylococcus aureus endocarditis

Background

We previously reported the use of a catheter system to damage the tricuspid valve and create infectious endocarditis (IE) in an animal model. The current study aims to create a faint IE model suitable for antibiotic prophylaxis using a low bacterial inoculum. We also aim to explore a way to quantitatively assess valvular impairment and to predict the success of the IE models during catheterization.

Methods

Ninety rabbits were assigned to two groups according to the density of bacteria inoculated (1 × 10⁵ CFU for Group A and 1 × 10⁴ CFU for Group B). A catheter system consisting of a polyethylene catheter and a guide wire were used to damage the valve. The catheter system was passed through the rabbits’ tricuspid valves under echocardiographic guidance. A pressure transducer was used to assess right atrial pressure (P_RA) before and just after valvular damage to calculate the pressure alterations (ΔP_RA). The animals in group A and B were divided into 3 subgroups according to the ΔP_RA (0–5 mmHg for Groups A₁ and B₁; 5–10 mmHg for Groups A₂ and B₂; 10–15 mmHg for Groups A₃ and B₃). Staphylococcus aureus (ATCC 29213) inoculation was performed 24 hr after cardiac catheterization.

Results

Faint IE was confirmed in 20%, 93.3%, 26.7%, 6.7%, 20%, and 33.3% of the rabbits in Groups A₁, A₂, A₃, B₁, B₂, and B₃, respectively. There was no difference in the LV/RV ratio and V_TR of the No-IE, faint-IE, and severe IE animals. Faint IE rabbits had a larger ΔP_RA than No-IE rabbits (7.81 ± 1.21 vs. 2.48 ± 1.0, P < 0.01, for Group A; 7.60 ± 1.32 vs. 2.98 ± 1.08, P < 0.01, for Group B). The ΔP_RA of severe IE and faint IE rabbits was significantly different (13.11 ± 1.31 vs. 7.81 ± 1.21, P < 0.01, for Group A; 12.73 ± 1.44 vs.7.60 ± 1.32, P < 0.01, for Group B).

Conclusion

ΔP_RA could be used to assess valvular impairment. Controlling the value of ΔP_RA during catheterization and inoculating of an appropriate dose of bacteria was associated with a successful IE model.

A rabbit model of right-sided Staphylococcus aureus endocarditis created with echocardiographic guidance

Background

The most widely used experimental models of infective endocarditis (IE) are the rabbit and rat models, in which cardiac valve lesions are induced by a polyethylene catheter introduced into the left ventricle through the aortic valve. Our study was designed to create a rabbit model of IE right-sided with echocardiographic guidance.

Methods

Thirty rabbits underwent both catheterization and inoculation (group A). These were divided into three subgroups of ten based on the time of catheter removal (immediately, after 24 h, and after death or moribundity for groups, A₁, A₂, and A₃, respectively). Ten inoculated-only and ten catheterized-only rabbits served as controls. A catheter system consisted of a polyethylene catheter and a guide wire inside it. This system was passed through the rabbits’ tricuspid valves under echocardiographic guidance to damage them. The ratio of left ventricle to right ventricle (LV/RV) was measured in a four-chamber view before catheterization and at the time of death or moribundity. The peak velocity of tricuspid regurgitation (V_TR) was measured in a four-chamber view at the time of catheterization and at the time of death or moribundity. Staphylococcus aureus (ATCC 29213) inoculation was performed 24 h after right heart catheterization to produce IE.

Results

IE was confirmed in 28 of 30 rabbits by macroscopic and histologic examination of tricuspid valves, blood cultures, and bacterial count in cardiac vegetations. Cardiac vegetations were confirmed in 25 of 28 IE rabbits by echocardiography. Enlargement of right ventricle dimension with a significantly decreased LV/RV ratio was confirmed in all IE rabbits at the time of death or moribundity than at the initial state (1.11 ± 0.35 vs. 1.95 ± 0.39, P < 0.01; 1.21 ± 0.34 vs. 1.98 ± 0.35, P < 0.01; 1.04 ± 0.31 vs. 2.00 ± 0.41, P < 0.01 for groups A₁, A₂, and A₃, respectively). V_TR was significantly higher in all the IE rabbits at the time of death or moribundity than at the time of catheterization (1.89 ± 0.46 vs 0.76 ± 0.45, P < 0.01; 2.04 ± 0.73 vs 0.68 ± 0.66, P < 0.01; 2.24 ± 0.51 vs 0.87 ± 0.55, P < 0.01 for group A₁, A₂ and A₃, respectively).

Conclusion

The models described herein closely reproduced the pathogenesis and pathophysiology of right heart catheter-induced endocarditis in humans. Echocardiographic guidance is helpful in the process of right heart catheterization. Some echocardiographic parameters, such as V_TR and the LV/RV ratio could be used to assess the success or failure of the IE models.

The guinea pig as a model of infectious diseases

The words 'guinea pig' are synonymous with scientific experimentation, but much less is known about this species than many other laboratory animals. This animal model has been used for approximately 200 y and was the first to be used in the study of infectious diseases such as tuberculosis and diphtheria. Today the guinea pig is used as a model for a number of infectious bacterial diseases, including pulmonary, sexually transmitted, ocular and aural, gastrointestinal, and other infections that threaten the lives of humans. Most studies on the immune response to these diseases, with potential therapies and vaccines, have been conducted in animal models (for example, mouse) that may have less similarity to humans because of the large number of immunologic reagents available for these other species. This review presents some of the diseases for which the guinea pig is regarded as the premier model to study infections because of its similarity to humans with regard to symptoms and immune response. Furthermore, for diseases in which guinea pigs share parallel pathogenesis of disease with humans, they are potentially the best animal model for designing treatments and vaccines. Future studies of immune regulation of these diseases, novel therapies, and preventative measures require the development of new immunologic reagents designed specifically for the guinea pig.

Therapeutic efficacy of GAR-936, a novel glycylcycline, in a rat model of experimental endocarditis

GAR-936, a novel glycylcycline, was investigated with a rat model of experimental endocarditis. It was compared with vancomycin against both vancomycin-susceptible and -resistant Enterococcus faecalis and methicillin-resistant Staphylococcus aureus. GAR-936 exhibited the lowest MICs (</=0.12 microgram/ml) in vitro against each of the isolates tested. Endocarditis was established by placement of a catheter across the aortic valve, followed by intravenous injection of 10(6) CFU of bacteria 48 h later. Treatment with GAR-936 or vancomycin was initiated 24 to 36 h after bacterial infection and administered subcutaneously twice a day for 3 days at ascending doses. GAR-936 reduced bacterial vegetation titers by >2 log(10) CFU, compared to those in untreated controls, for both vancomycin-susceptible and -resistant (VanA and VanB) E. faecalis strains and >4 log(10) CFU for a methicillin-resistant S. aureus isolate. The glycylcycline was more efficacious at a lower administered dose in the rat model of endocarditis than was vancomycin. The efficacy of GAR-936 in this model was apparently not enhanced by a factor in rat serum, as was observed for vancomycin with a time-kill curve. The results of this study demonstrate the therapeutic potential of GAR-936 for the treatment of enterococcal and staphylococcal infections and warrant further investigation.

Infective endocarditis: new concepts in pathogenesis

Gram-positive cocci account for the large majority of cases of infective endocarditis. Pathogenesis investigations of endocarditis have therefore focused on purported virulence factors in staphylococci, viridans group streptococci and enterococci. In addition to novel molecular techniques that have been adapted for use in the examination of gram-positive cocci, animal models of experimental endocarditis have been employed to support or discount the role of specific bacterial components in production of infective endocarditis. This review details recent work that addresses endocarditis pathogenesis and highlights pertinent findings from these investigations.