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

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 was 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.