BackgroundSince the appearance of COVID-19 in January 2020, invasive bacterial infections have decreased significantly worldwide. However, alterations in age and sex distributions, clinical forms, phenotypes, and genotypes of isolates have not been analyzed. Our goal is to present and discuss these data considering the current COVID-19 pandemic situation. Methods: The data of the national reference center for meningococci and Haemophilus influenzae in France were mined to examine the above aspects of invasive bacterial infection before (2018–2019) and after (2020–2021) the COVID-19 pandemic. Detailed epidemiological, clinical, and microbiological data were collected, and whole genome sequencing was carried out on meningococcal isolates (n = 1466). Results: In addition to the overall decline in the number of cases, various changes in age, sex, and phenotypes of isolates were also noted. As for N. meningitidis, more cases were observed in adults, as well as more invasive pneumopathies. Furthermore, fewer hyperinvasive meningococcal genotypes have circulated since COVID-19 emerged. The situation has been different for H. influenzae, as the number of invasive cases among adults decreased due to a reduction in non-typeable isolates. In contrast, cases due to serotypeable isolates, particularly serotypes a and b, increased in children <5 years-old. Conclusions: It is possible that measures implemented to stop COVID-19 may have reduced the circulation of N. meningitidis and H. influenzae isolates, but to a variable extent. This may be due to differences in circulation between these two species according to age groups. Vaccination schedules against these two species may have also influenced the evolution of these invasive bacterial infections since the emergence of the COVID-19 pandemic.

Infections by Neisseria meningitidis show duality between frequent asymptomatic carriage and occasional life-threatening disease. Bacterial and host factors involved in this balance are not fully understood. Cytopathic effects and cell damage may prelude to pathogenesis of isolates belonging to hyper-invasive lineages. We aimed to analyze cell–bacteria interactions using both pathogenic and carriage meningococcal isolates. Several pathogenic isolates of the ST-11 clonal complex and carriage isolates were used to infect human epithelial cells. Cytopathic effect was determined and apoptosis was scored using several methods (FITC-Annexin V staining followed by FACS analysis, caspase assays and DNA fragmentation). Only pathogenic isolates were able to induce apoptosis in human epithelial cells, mainly by lipooligosaccharide (endotoxin). Bioactive TNF-α is only detected when cells were infected by pathogenic isolates. At the opposite, carriage isolates seem to provoke shedding of the TNF-α receptor I (TNF-RI) from the surface that protect cells from apoptosis by chelating TNF-α. Ability to induce apoptosis and inflammation may represent major traits in the pathogenesis of N. meningitidis. However, our data strongly suggest that carriage isolates of meningococci reduce inflammatory response and apoptosis induction, resulting in the protection of their ecological niche at the human nasopharynx. Acquisition of Neisseria meningitidis often leads to asymptomatic colonization (carriage) and rarely results in invasive disease associated with tissue injury. The reasons that make disease-associated isolates (pathogenic isolates) but not asymptomatic carriage isolates able to invade the host to establish disease are not understood. Isolates belonging to the ST-11 clonal complex are most frequently associated with the disease and rarely found in carriers. These hyper-invasive isolates may be able to induce cytopathic effects in target cells. We aimed to investigate the cytopathic effect of meningococcal isolates on epithelial cells using both ST-11 pathogenic isolates and carriage isolates. We showed that cytopathic effects were strongly associated with pathogenic isolates and infected cells exhibited features of apoptosis. This effect is mainly mediated by bacterial endotoxin (lipooligosaccharide) and involved an autocrine signaling mechanism of secreted TNF-α through its receptor TNF-RI. In contrast, carriage isolates down-regulate TNF-RI on the surface of infected cells by increasing TNF-RI shedding into the medium. We suggest that chelating secreted TNF-α protects cells from apoptosis. Our results unravel a differential modulation of TNF-α signaling by meningococcal isolates leading to cell survival or death and would therefore contribute to better understanding of the duality between carriage and invasiveness.

Invasive meningococcal disease (IMD) cases declined upon the implementation of non-pharmaceutical measures to control the COVID-19 pandemic. A rebound in IMD cases was feared upon easing these measures. We conducted a retrospective descriptive study using the French National Reference Center Database for meningococci between 2015 and 2022. We scored serogroups, sex, age groups, and clonal complexes of the corresponding isolates. Our data clearly show a decline in the number of IMD cases for all serogroups and age groups until 2021. This decline was mainly due to a decrease in IMD cases provoked by the hyperinvasive ST-11 clonal complex. However, since the fall of 2021, there has been an increase in IMD cases, which accelerated in the second half of 2022. This rebound concerned all age groups, in particular 16-24 years. The increase in cases due to serogroups B, W, and Y were mainly due to the expansion of isolates of the ST-7460, the clonal complex ST-9316 and the clonal complex ST-23, respectively. IMD epidemiology changes constantly and profound epidemiological changes have been recently observed. The surveillance of IMD needs to be enhanced using molecular tools. Additionally, vaccination strategies need to be updated to acknowledge recent epidemiological changes of these vaccine-preventable serogroups.

Early differential diagnosis between acute bacterial and viral meningitis is problematic. We aimed to investigate whether the detection of lipocalin 2, a protein of the acute innate immunity response, may be used as a marker for acute bacterial meningitis.

Haemophilus influenzae is a prevalent agent of respiratory infections, including acute otitis media (AOM), that lead to high antibiotic prescription and may contribute to the development of bacterial resistance to antibiotics. The objective of this work was to describe and analyse antibiotic resistance of H. influenzae from 2017 to 2021 in France. We characterized H. influenzae isolates transmitted to the French national reference centre for H. influenzae between 2017 and 2021. We included all the 608 non-invasive respiratory isolates. Resistance rates to the main antibiotics were described. The relationship between resistance rate, age, and sex of patients and germ serotype was investigated. Isolates were mainly from alveolar lavage (29.3%), expectoration (22.9%), or sputum (15%). Resistance to amoxicillin (61.4%), amoxicillin/clavulanic acid (47.4%), and cefotaxime (39.3%) was high and correlated with the presence of β-lactamase and/or modifications of the ftsI gene encoding penicillin-binding protein 3. Resistance to sulfamethoxazole/trimethoprim (33.2%) was more moderate. There were no significant differences according to serotype, age, or gender. The benefit/risk balance of first choice use of amoxicillin and even of amoxicillin/clavulanic acid in AOM is questionable in view of the significant resistance to H. influenzae. The use of sulfamethoxazole/trimethoprim could be an alternative but may still need further evaluation.

Differential modulation of NF-κB during meningococcal infection is critical in innate immune response to meningococcal disease. Non-invasive isolates of Neisseria meningitidis provoke a sustained NF-κB activation in epithelial cells. However, the hyperinvasive isolates of the ST-11 clonal complex (ST-11) only induce an early NF-κB activation followed by a sustained activation of JNK and apoptosis. We show that this temporal activation of NF-κB was caused by specific cleavage at the C-terminal region of NF-κB p65/RelA component within the nucleus of infected cells. This cleavage was mediated by the secreted 150 kDa meningococcal ST-11 IgA protease carrying nuclear localisation signals (NLS) in its α-peptide moiety that allowed efficient intra-nuclear transport. In a collection of non-ST-11 healthy carriage isolates lacking NLS in the α-peptide, secreted IgA protease was devoid of intra-nuclear transport. This part of iga polymorphism allows non-invasive isolates lacking NLS, unlike hyperinvasive ST-11 isolates of N. meningitides habouring NLS in their α-peptide, to be carried asymptomatically in the human nasopharynx through selective eradication of their ability to induce apoptosis in infected epithelial cells. Strains of Neisseria meningitidis isolated from patients induce apoptotic cell death, whereas strains isolated from healthy carriage isolates do not. Part of the difference has been shown to arise from differential modulation of NF-κB during meningococcal infection. While non-invasive isolates of Neisseria meningitidis provoke a sustained NF-κB activation in epithelial cells, hyperinvasive isolates only induce an early NF-κB activation followed by a sustained activation of JNK and apoptosis. Here, we elucidate the mechanism conferring this differential modulation, specifically showing that ST-11 hyperinvasive isolates promote specific cleavage of NF-κB p65/RelA component in a manner dependent on the secreted IgA protease. This cleavage occurs within the nuclear compartment. Secreted IgA protease from non-invasive isolates was unable to reach the nuclear compartment of infected cells, resulting in a sustained activation of NF-κB activity and subsequent cytoprotective effect. Modulation of NF-κB-related signaling is likely a double-edged sword to decide the fate of meningococcal infection.