Potential of the fluoroketolide RBx 14255 against Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae in an experimental murine meningitis model

Developing a Novel Murine Meningococcal Meningitis Model Using a Capsule-Null Bacterial Strain

BACKGROUND

Neisseria meningitidis (meningococcus) is a Gram-negative bacterium that colonises the nasopharynx of about 10% of the healthy human population. Under certain conditions, it spreads into the body, causing infections with high morbidity and mortality rates. Although the capsule is the key virulence factor, unencapsulated strains have proved to possess significant clinical implications as well. Meningococcal meningitis is a primarily human infection, with limited animal models that are dependent on a variety of parameters such as bacterial virulence and mouse strain. In this study, we aimed to develop a murine Neisseria meningitidis meningitis model to be used in the study of various antimicrobial compounds.

METHOD

We used a capsule-deficient Neisseria meningitidis strain that was thoroughly analysed through various methods. The bacterial strain was incubated for 48 h in brain-heart infusion (BHI) broth before being concentrated and injected intracisternally to bypass the blood-brain barrier in CD-1 mice. This prolonged incubation time was a key factor in increasing the virulence of the bacterial strain. A total of three more differently prepared inoculums were tested to further solidify the importance of the protocol (a 24-h incubated inoculum, a diluted inoculum, and an inactivated inoculum). Antibiotic treatment groups were also established. The clinical parameters and number of deaths were recorded over a period of 5 days, and comatose mice with no chance of recovery were euthanised.

RESULTS

The bacterial strain was confirmed to have no capsule but was found to harbour a total of 56 genes coding virulence factors, and its antibiotic susceptibility was established. Meningitis was confirmed through positive tissue culture and histological evaluation, where specific lesions were observed, such as perivascular sheaths with inflammatory infiltrate. In the treatment groups, survival rates were significantly higher (up to 81.25% in one of the treatment groups compared to 18.75% in the control group).

CONCLUSION

We managed to successfully develop a cost-efficient murine (using simple CD-1 mice instead of expensive transgenic mice) meningococcal meningitis model using an unencapsulated strain with a novel method of preparation.

Novel fluorobenzothiazole as a dual inhibitor of gyrase B and topoisomerase IV against Gram-positive pathogens

Aim: The development of a novel inhibitor targeting gyrase B and topoisomerase IV offers an opportunity to combat multidrug resistance. Methods: We investigated the activity of RBx 10080758 against Gram-positive bacteria in vitro and in vivo. Results: RBx 10080758 showed a potent 50% inhibitory concentration of 0.13 μM and 0.25 μM against gyrase B and topoisomerase IV, respectively, and exhibited strong whole-cell in vitro activity with MIC ranges of 0.015-0.06 and 0.015-0.03 μg/ml against Staphylococcus aureus and Streptococcus pneumoniae, respectively. In a rat thigh infection model with methicillin-resistant S. aureus, RBx 10080758 at 45 mg/kg exhibited a >3 log10 CFU reduction in thigh muscles. Conclusion: RBx 10080758 displayed potent activity against multiple multidrug-resistant Gram-positive bacteria with a dual-targeting mechanism of action.

Enantioselective Fluorination of α-Substituted β-Diketones Using β,β-Diaryl Serines

We report the enantioselective fluorination of α-substituted β-diketones using β,β-diaryl serines as a primary amine organocatalyst. The reaction affords the corresponding fluorinated products in yields of 74 to 99% with excellent enantioselectivity (75-95% ee). Moreover, for synthetic applications, the diol, aldols, and the allylic fluoride were synthesized from 2a, maintaining excellent enantioselectivity (94% ee). The control experiment reveals that the CO₂H group of the β,β-diaryl serines plays an important role in inducing the high enantioselectivity.

The search for novel treatment strategies for Streptococcus pneumoniae infections

This review provides an overview of the most important novel treatment strategies against Streptococcus pneumoniae infections published over the past 10 years. The pneumococcus causes the majority of community-acquired bacterial pneumonia cases, and it is one of the prime pathogens in bacterial meningitis. Over the last 10 years, extensive research has been conducted to prevent severe pneumococcal infections, with a major focus on (i) boosting the host immune system and (ii) discovering novel antibacterials. Boosting the immune system can be done in two ways, either by actively modulating host immunity, mostly through administration of selective antibodies, or by interfering with pneumococcal virulence factors, thereby supporting the host immune system to effectively overcome an infection. While several of such experimental therapies are promising, few have evolved to clinical trials. The discovery of novel antibacterials is hampered by the high research and development costs versus the relatively low revenues for the pharmaceutical industry. Nevertheless, novel enzymatic assays and target-based drug design, allow the identification of targets and the development of novel molecules to effectively treat this life-threatening pathogen.