Introduction: A Neisseria meningitidis carrier study has been conducted among students at Örebro university in Sweden in 2018 and 2019. Pharyngeal samples were collected from 3489 students. PCR for the genes ctrA and crgA was run on all samples. The positive samples were then cultured on agar plates to find the N. meningitidis. In 349 of the PCR positive samples, no N. meningitidis could be isolated, which raised the question if other bacteria could have these genes. The most likely bacteria to have these genes were assumed to be other species within the genus Neisseria. Aim: To identify whether other neisserial species have the ctrA and crgA genes. Methods: The 349 samples were cultured on agar plates for two days. The species were then identified by MALDI-TOF MS. The isolated Neisserial species and some other species as controls were saved. PCR for ctrA and crgA genes were then run on these bacteria to determine whether they possessed these genes. Results: Five N. meningitidis that had been missed by the first round of culture were identified. Seventy-five other colonies of neisserial species were isolated. N. subflava (n=40) were the most common. Nine (12 %) were crgA positive but none were ctrA positive. At least one crgA positive colony was found in four of the five different non-meningococcal neisserial species isolated in this study. Conclusion: The crgA gene seems quite common among non-meningococcal neisserial species while ctrA seems to be specific for N. meningitidis

Neisseria meningitidis (Nm) est un germe commensal du rhinopharynx ayant pour seul hôte l’homme. Malgré un portage asymptomatique largement répandu, et pour des raisons encore inconnues, elle peut échapper au système immunitaire de l’hôte et devenir pathogène provoquant ainsi méningite et septicémie pouvant être mortelles principalement chez les enfants. Au cours du processus infectieux, Nm alterne entre des phases de colonisation et de dissémination, et se retrouve alors confrontée à différents environnements. L’adaptation rapide à ces variations, par modulation de l’expression des gènes de virulence, représente un facteur important dans sa pathogénie. Les facteurs qui contribuent à la virulence de Nm sont essentiellement des structures présentes à la surface de la bactérie parmi lesquelles les pili et la capsule. Les gènes codant ces facteurs sont sous le contrôle de la protéine CrgA, régulateur transcriptionnel de la famille LysR qui intervient lors de l’adhésion de Nm aux cellules humaines. La protéine CrgA régule négativement sa propre expression ainsi de celle des gènes impliqués dans la synthèse de la capsule (sia) et des pili (pilE et pilC1). Par ailleurs, le PTS est un système de transduction du signal qui intervient, par phosphorylation ou via des interactions protéine/protéine, dans le transport des sucres et dans la régulation du métabolisme du carbone. Chez Nm, ce système est incomplet (constitué des protéines EI, HPr, et deux EIIA), il n’est donc pas fonctionnel pour le transport des sucres mais aurait pu conserver ses fonctions régulatrices. Nous avons montré que les protéines du PTS de Nm étaient actives in vitro et in vivo et que la cascade de phosphorylation du PTS était fonctionnelle. Nous avons également montré que l’inactivation du gène ptsH, codant la protéine HPr, entrainait une diminution significative de la synthèse de la capsule, une augmentation de l’adhésion du mutant aux cellules épithéliales humaines et une augmentation de l’expression de crgA. De ce fait, l’absence de l’HPr semble empêcher la répression de crgA et par conséquent celle des gènes sia. Par ailleurs, des expériences de co-immunoprécipitation, nous ont permis de mettre en évidence que l’HPr interagissait directement avec la protéine CrgA in vitro et in vivo. Ces résultats suggèrent que la protéine HPr interviendrait dans la régulation de l’expression des gènes de virulence de Nm via la régulation de l’expression de crgA. Ainsi, un lien entre métabolisme du carbone et virulence a été mis en évidence chez Nm. / Neisseria meningitidis (Nm) is a commensal bacterium of the nasopharynx, which only colonizes humans. Despite a large number of asymptomatic carriers, and for reasons so far unknown, Nm occasionally becomes virulent, escaping the host’s immune system and causing septicaemia and meningitis, the latter being potentially lethal, mostly in children.During the infectious process, Nm alternates between phases of colonization and dissemination, each time facing different environments. This rapid adaptation to the changing environment occurs via the modulation of the expression of virulence genes and represents an important factor of pathogenicity. The structures involved in virulence in Nm are mainly present at the surface of the bacterium, including the pili and the capsule. The genes coding for these structures are controlled by the CrgA protein, a transcriptional regulator of the LysR family, which is induced during the adhesion of Nm to human cells. CrgA negatively regulates its own expression as well as the expression of those genes implicated in the synthesis of the capsule (sia) and pili (pilE and pilC1).Moreover, the PTS is a signal transduction system, which is involved, via phosphorylation or protein/protein interactions, in the transport of sugars and the regulation of the carbon metabolism. In Nm, the PTS is incomplete (only composed of the proteins EI, HPr and two EIIA), thus not functioning in the transport of sugars but it may have conserved regulatory functions.In this work, we demonstrate that the PTS proteins in Nm are active in vitro and in vivo and that the phosphorylation cascade of the PTS is functional. We further show that the inactivation of the ptsH gene, coding for the HPr protein, significantly reduces the synthesis of the capsule, enhances the adhesion of the mutants to human epithelial cells and increases the expression of crgA. Thus, the absence of HPr seems to inhibit the repression of crgA and as a consequence also the repression of the sia genes. Furthermore, from co-immunoprecipitation experiments we provide evidence that HPr directly interacts with the CrgA protein in vitro and in vivo. These results suggest that the HPr protein in Nm regulates the expression of the virulence genes via the regulation of crgA expression. Thus, we provide evidence of a link between carbon metabolism and virulence in Nm.