The microbiota and the gut-brain axis: insights from the temporal and spatial mucosal alterations during colonisation of the germfree mouse intestine

The influence of the gut microbiota on the nervous system, brain development and behaviour, in particular during microbial colonisation of the host, has recently been receiving profound interest. Our time-resolved mining of combined data analyses of the ex-germfree mouse intestine during a 30-day course of colonisation with conventional mouse faecal microbiota (conventionalisation), shed light on temporal altered expression of genes of which the products influenced functions of the nervous system. Plasma tryptophan and kynurenine levels reflected high indoleamine dioxygenase activity, which was supported by significant temporal induction of the encoding gene in all gut tissues. However, the majority of genes associated with neuronal development and function were reduced. Colonic substance P elevation in response to conventionalisation was higher only after 30-days. These results support a functional microbiota-neurohumoral relationship during conventionalisation and suggest a delayed neuronal response that is elicited only after the microbiota accommodating homeostasis has been accomplished.

Vibrio cholerae Phosphoenolpyruvate Phosphotransferase System Control of Carbohydrate Transport, Biofilm Formation, and Colonization of the Germfree Mouse Intestine

ABSTRACT The bacterial phosphoenolpyruvate phosphotransferase system (PTS) is a highly conserved phosphotransfer cascade whose components modulate many cellular functions in response to carbohydrate availability. Here, we further elucidate PTS control of Vibrio cholerae carbohydrate transport and activation of biofilm formation on abiotic surfaces. We then define the role of the PTS in V. cholerae colonization of the adult germfree mouse intestine. We report that V. cholerae colonizes both the small and large intestines of the mouse in a distribution that does not change over the course of a month-long experiment. Because V. cholerae possesses many PTS-independent carbohydrate transporters, the PTS is not essential for bacterial growth in vitro. However, we find that the PTS is essential for colonization of the germfree adult mouse intestine and that this requirement is independent of PTS regulation of biofilm formation. Therefore, competition for PTS substrates may be a dominant force in the success of V. cholerae as an intestinal pathogen. Because the PTS plays a role in colonization of environmental surfaces and the mammalian intestine, we propose that it may be essential to successful transit of V. cholerae through its life cycle of pathogenesis and environmental persistence.

Optimizing the Germfree Mouse Model for In Vivo Evaluation of Oral Vibrio cholerae Vaccine and Vector Strains

ABSTRACT The germfree mouse model of Vibrio cholerae infection can be used to judge immune responses to V. choleraevaccine and vector strains. In the original model, a single oral inoculation was administered on day 0, a booster oral inoculation was administered on day 14, and immune responses were analyzed with samples collected on day 28. Unfortunately, immune responses in this model frequently were low level, and interanimal variability occurred. In order to improve this model, we evaluated various primary and boosterV. cholerae inoculation schedules. The most prominent systemic and mucosal antibody responses were measured in mice that received a multiple primary inoculation series on days 0, 2, 4, and 6 and booster inoculations on days 28 and 42. These modifications result in improved preliminary evaluation of V. cholerae vaccine and vector strains in mice.