Midgut Volvulus Adds a Murine, Neutrophil-Driven Model of Septic Condition to the Experimental Toolbox

BACKGROUND

Severe infections that culminate in sepsis are associated with high morbidity and mortality. Despite continuous efforts in basis science and clinical research, evidence based-therapy is mostly limited to basic causal and supportive measures. Adjuvant therapies often remain without clear evidence. The objective of this study was to evaluate the septic volvulus ischemia-reperfusion model in comparison to two already established models and the role of neutrophil extacellular traps (NETs) in this model.

METHODS

The technique of the murine model of midgut volvulus was optimized and was compared to two established models of murine sepsis, namely cecal ligation and puncture (CLP) and intra-peritoneal (i.p.) injection of lipopolysaccharide (LPS).

RESULTS

Midgut volvulus for 15 min caused a comparable mortality (38%) as CLP (55%) and peritoneal LPS injection (25%) at 48 h. While oxidative stress was comparable, levels of circulating free DNA (cfDNA), and splenic/hepatic and pulmonary translocation of bacteria were decreased and increased, respectively at 48 h. DNases were increased compared to the established models. Proteomic analysis revealed an upregulation of systemic Epo, IL-1b, Prdx5, Parp1, Ccl2 and IL-6 at 48 h in comparison to the healthy controls.

DISCUSSION AND CONCLUSION

Midgut volvulus is a stable and physiological model for sepsis. Depending on the duration and subsequent tissue damage, it represents a combination of ischemia-reperfusion injury and hyperinflammation.

RELSA-A multidimensional procedure for the comparative assessment of well-being and the quantitative determination of severity in experimental procedures

Good science in translational research requires good animal welfare according to the principles of 3Rs. In many countries, determining animal welfare is a mandatory legal requirement, implying a categorization of animal suffering, traditionally dominated by subjective scorings. However, how such methods can be objectified and refined to compare impairments between animals, subgroups, and animal models remained unclear. Therefore, we developed the RELative Severity Assessment (RELSA) procedure to establish an evidence-based method based on quantitative outcome measures such as body weight, burrowing behavior, heart rate, heart rate variability, temperature, and activity to obtain a relative metric for severity comparisons. The RELSA procedure provided the necessary framework to get severity gradings in TM-implanted mice, yielding four distinct RELSA thresholds L1<0.27, L2<0.59, L3<0.79, and L4<3.45. We show further that severity patterns in the contributing variables are time and model-specific and use this information to obtain contextualized between animal-model and subgroup comparisons with the severity of sepsis > surgery > restraint stress > colitis. The bootstrapped 95% confidence intervals reliably show that RELSA estimates are conditionally invariant against missing information but precise in ranking the quantitative severity information to the moderate context of the transmitter-implantation model. In conclusion, we propose the RELSA as a validated tool for an objective, computational approach to comparative and quantitative severity assessment and grading. The RELSA procedure will fundamentally improve animal welfare, data quality, and reproducibility. It is also the first step toward translational risk assessment in biomedical research.

NOX2 Deficiency Permits Sustained Survival of S. aureus in Macrophages and Contributes to Severity of Infection

Although the crucial role of professional phagocytes for the clearance of S. aureus infections is well-established, several studies indicate an adverse role of leukocytes in the dissemination of S. aureus during infection. Since only little is known about macrophages in this context, we analyzed the role of macrophages, and in particular reactive oxygen species deficiency, for the seeding of S. aureus metastases. Infection of bone marrow-derived macrophages (BMDM) with S. aureus revealed that NADPH oxidase 2 (NOX2-) deficient, but not NOX1- or NOX4-deficient, BMDM failed to clear intracellular S. aureus. Despite of larger intracellular bacterial burden, NOX2-deficient BMDM showed significantly improved survival. Intravenous injection of mice with in vitro-infected BMDMs carrying intracellular viable S. aureus led to higher bacterial loads in kidney and liver of mice compared to injection with plain S. aureus. An even higher frequency of liver abscesses was observed in mice infected with S. aureus-loaded nox2 ^-/- BMDM. Thus, the improved intracellular survival of S. aureus and improved viability of NOX2-deficient BMDM is associated with an aggravated metastatic dissemination of S. aureus infection. A combination of vancomycin and the intracellularly active antibiotic rifampicin led to complete elimination of S. aureus from liver within 48 h, which was not achieved with vancomycin treatment alone, underscoring the impact of intracellular S. aureus on the course of disease. The results of our study indicate that intracellular S. aureus carried by macrophages are sufficient to establish a systemic infection. This suggests the inclusion of intracellularly active antibiotics in the therapeutic regimen of invasive S. aureus infections, especially in patients with NADPH oxidase deficiencies such as chronic granulomatous disease.

Exploitation of two siderophore receptors, BauA and BfnH, for protection against Acinetobacter baumannii infection

Iron uptake system is expressed in early stages of Acinetobacter baumannii infections under iron-restricted conditions. This study is aimed at the evaluation of immuno-protectivity of BfnH in comparison with BauA in both mature and selected fragmental proteins. The study was designed in single and combined forms of antigens. BfnH is presented in 3472 strains of A. baumannii with more than 97% identity. The preliminary immune-informatics analysis of this protein indicated a region from the β-barrel domain including exposed loops 2-5, with antigenic score comparable to that of BfnH. There was a significant rise in the specific IgG response in all test groups. The bacterial challenge with a lethal dose of A. baumannii demonstrated partial protection of whole proteins which coincides with a significant reduction in the bacterial population colonized in the main organs and an increase in the survival level. Passive immunization of the mice brought about 50% survival in the mice groups immunized with BfnH and with a combination of BfnH and BauA. The protectivity of siderophore receptors suggests their potential immunogenic role that could be considered as a component of multivalent subunit vaccine candidates against A. baumannii.

Antiquorum Sensing Activity of Seed Oils from Oleaginous Plants and Protective Effect During Challenge with Chromobacterium violaceum

Seed oils from oleaginous plants are rich in fatty acids (FAs) that play important roles in the health of the consumers. Recent studies indicate that FA also can play an important role in communication and regulation of virulence in bacteria. Nevertheless, evidence demonstrating protection against bacterial infections mediated by their quorum sensing inhibition (QSI) activity is scarce. In this study, sunflower, chia, and amaranth oils, were assayed for their QSI capacity by inhibiting violacein production and alkaline exoprotease activity of Chromobacterium violaceum. In vitro assays revealed that the oils exhibited QSI activities, whereas in vivo they delayed death of mice inoculated intraperitoneally with the bacterium. Gas chromatography coupled with mass spectrometry analysis of the oils indicated the presence of saturated FA (SAFA) and unsaturated FA as main components. Through a structure-activity relationship study of free FAs, bactericidal effect was identified mainly for polyunsaturated FAs, whereas QSI activity was restricted to SAFA of chains 12-18 carbon atoms in length. These data correlate with a possible interaction suggested by molecular docking analysis of lauric, myristic, and stearic acids with the CviR protein. Our study highlights the antiquorum sensing potential of SAFA, which may be future antivirulence therapeutic agents for the treatment of bacterial infections.

Purified citritin in combination with vancomycin inhibits VRE in vitro and in vivo

Gram-positive pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VRE) have been frequently associated with bacterial resistance mechanisms. These mechanisms, in turn, restrict a range of therapeutic opportunities for the treatment of infections caused by these micro-organisms. Faced with this problem, the present study aims to isolate and characterize molecules with antimicrobial activity derived from the fungus Penicillium citrinum isolated from Cerrado soil. Furthermore, we also tested possible antibacterial potential alone and in combination with commercial antimicrobial agents. In this context, citrinin was isolated and characterized by nuclear magnetic resonance and electrospray ionization. Functional analyses showed MIC of 128 µg ml^-1 against S. aureus ATCC 25923, E. faecalis ATCC 29212 and a clinical isolate of vancomycin-resistant E. faecium (VRE01). However, for a clinical strain of methicillin-resistant S. aureus (MRSA01), the MIC was 256 µg ml^-1. In order to avoid such high concentrations and reduce the collateral effects, additive effects were evidenced by combining citrinin with cefoxitin against MRSA01 (FIC index=0.5) and also citrinin with vancomycin toward VRE01 (FIC index=0.5). In vivo studies with BALB/c-tipe mice (MRSA assay) demonstrated a clinical ineffectiveness of cefoxitin associated with citrinin (9.8 mg kg^-1 of cefoxitin +0.2 mg kg^-1 of citrinin), with this combination being inefficient to increase animal survival. However, the combination used in the treatment of VRE (23.5 mg kg^-1 of citrinin +1.5 mg kg^-1 of vancomycin) sepsis model was extremely promising, leading to an animal survival rate of 80 percent. In summary, our data show, for the first time, the possible successful use of citrinin associated with vancomycin for pathogenic bacteria control.