In vitro phenotypic and transcriptomic variation in Neisseria musculi morphotypes correlate with colonization variability and persistence in vivo

Abstract

Asymptomatic colonization of the upper respiratory tract is a common trait of the two human restricted pathogens, Neisseria gonorrhoeae and Neisseria meningitidis. In vivo models of pathogenic neisserial infections are heterologous systems that permit short-term colonization but do not fully recapitulate infections in humans. Studying Neisseria musculi (Nmus), an oral commensal, in laboratory mice allows investigation of Neisseria-host interactions that avoids host restriction barriers. Nmus produces smooth and rough morphotypes on solid media. We compared the in vitro phenotypes, biofilm transcriptomes, in vivo colonization patterns and burdens of the two Nmus morphotypes. We observed that the two morphotypes differ in biofilm formation, pilin production, transformation frequency, and aggregation in vitro. These phenotypes strongly correlated with differential expression of a set of genes in the Nmus biofilms including those that encoded factors for bacterial attachment. In vivo, the smooth morphotype stably colonized the oral cavities of all inoculated A/J and C57BL/6J mice at higher burdens relative to the rough. Interestingly, both morphotypes colonized the oral cavities of A/Js at higher magnitudes than in C57BL/6Js. Gut colonization by the smooth morphotype was qualitatively higher than the rough. Nasal colonization in the A/Js were transient following nasal inoculations. Collectively, our results demonstrate that colonization by Nmus can be affected by various factors including Nmus morphotypes, inoculation routes, anatomical niches, and host backgrounds. The Nmus-mouse model can use variable morphotype-host combinations to study the dynamics of neisserial asymptomatic colonization and persistence in multiple extragenital niches. IMPORTANCEAnimal models for human adapted pathogenic Neisseria spp. do not fully mimic human infections and are complicated by host restriction barriers that can hinder long-term persistence. Such barriers can be avoided by studying Neisseria spp. native to the animal host used for disease models. Neisseria musculi (Nmus) isolated from wild mice colonizes the oral cavity and gut of laboratory mice for extended periods. Nmus shares host interaction factors with species pathogenic to humans and thus provides a native system to study orthologs of factors that may facilitate asymptomatic colonization and persistence in the human upper respiratory tract. We investigated the Nmus-mouse system to compare in vitro and in vivo phenotypes of two Nmus morphotypes. Our results support the hypothesis that the two morphotypes vary in different aspects of Neisseria-host interactions. Future use of the Nmus-host system will help identify molecular mechanisms required for neisserial asymptomatic colonization, dissemination, and persistence.