The evolutionary timing and spread of the Mycobacterium tuberculosis complex (MTBC), one of the most successful groups of bacterial pathogens, remains largely unknown. Here, using mycobacterial tandem repeat sequences as genetic markers, we show that the MTBC consists of two independent clades, one composed exclusively of M. tuberculosis lineages from humans and the other composed of both animal and human isolates. The latter also likely derived from a human pathogenic lineage, supporting the hypothesis of an original human host. Using Bayesian statistics and experimental data on the variability of the mycobacterial markers in infected patients, we estimated the age of the MTBC at 40,000 years, coinciding with the expansion of “modern” human populations out of Africa. Furthermore, coalescence analysis revealed a strong and recent demographic expansion in almost all M. tuberculosis lineages, which coincides with the human population explosion over the last two centuries. These findings thus unveil the dynamic dimension of the association between human host and pathogen populations.

SummaryThe population genomics of Pseudomonas aeruginosa was analysed by genome sequencing of representative strains of the 15 most frequent clonal complexes in the P. aeruginosa population and of the five most common clones from the environment of which so far no isolate from a human infection has been detected. Gene annotation identified 5892-7187 open reading frame (ORFs; median 6381 ORFs) in the 20 6.4-7.4 Mbp large genomes. The P. aeruginosa pangenome consists of a conserved core of at least 4000 genes, a combinatorial accessory genome of a further 10 000 genes and 30 000 or more rare genes that are present in only a few strains or clonal complexes. Whole genome comparisons of single nucleotide polymorphism synteny indicated unrestricted gene flow between clonal complexes by recombination. Using standardized acute lettuce, Galleria mellonella and murine airway infection models the full spectrum of possible host responses to P. aeruginosa was observed with the 20 strains ranging from unimpaired health following infection to 100% lethality. Genome comparisons indicate that the differential genetic repertoire of clones maintains a habitat-independent gradient of virulence in the P. aeruginosa population.

BackgroundSince the discovery of the human CFTR gene in 1989 various mouse models for cystic fibrosis (CF) have been generated and used as a very suitable and popular tool to approach research on this life-threatening disease. Age related changes regarding the course of disease and susceptibility towards pulmonary infections have been discussed in numerous studies.MethodsHere, we investigated CftrTgH(neoim)Hgu and Cftrtm1Unc-Tg(FABPCFTR)1Jaw/J CF mice and their non-CF littermates during an acute lung infection with Pseudomonas aeruginosa for age dependent effects of their lung function and immune response.Mice younger than three or older than six months were intratracheally infected with P. aeruginosa TBCF10839. The infection was monitored by lung function of the animals using non-invasive head-out spirometry and the time course of physiological parameters over 192 hours. Quantitative bacteriology and lung histopathology of a subgroup of animals were used as endpoint parameters.ResultsAge-dependent changes in lung function and characteristic features for CF like a shallower, faster breathing pattern were observed in both CF mouse models in uninfected state. In contrast infected CF mice did not significantly differ from their non-CF littermates in susceptibility and severity of lung infection in both mouse models and age groups. The transgenic Cftrtm1Unc-Tg(FABPCFTR)1Jaw/J and their non-CF littermates showed a milder course of infection than the CftrTgH(neoim)Hgu CF and their congenic C57Bl/6J non-CF mice suggesting that the genetic background was more important for outcome than Cftr dysfunction.ConclusionsPrevious investigations of the same mouse lines have shown a higher airway susceptibility of older CF mice to intranasally applied P. aeruginosa. The different outcome of intranasal and intratracheal instillation of bacteria implies that infected CF epithelium is impaired during the initial colonization of upper airways, but not in the subsequent response of host defense.

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Background: Classic infection models in rodents use lethal doses of bacteria as inocula, thus creating models which are rarely comparable to the clinical situation. Moreover, single time-point evaluation requires killing of the animals, necessitating large numbers of animals. Longitudinal parameters such as temperature appear to have a relatively low accuracy. Spirometry might be an accurate method to assess the course of a bacterial lung infection without the necessity to sacrifice the animals. Objectives: We measured lung function in C57BL/6JZtm mice following intratracheal infection with Pseudomonas aeruginosa and compared it to physiological parameters and lung histology. Methods: Head-out spirometry measuring 14 parameters was performed on C57BL6/J mice for eight days following a P. aeruginosa lung infection. Additionally rectal temperature, body weight and condition were assessed together with histological data and bacteriological clearance. Results: Several spirometric parameters were significantly altered for more than 72 h after inoculation, which was four times longer than observed alterations in physiological parameters such as temperature. Volume (amount of air inspired) decreased more than seven-fold within 6 h after inoculation and required 72 h to recover, rendering it the most sensitive spirometric parameter investigated. Spirometric and histological data correlated well. Conclusions: Our findings suggest that non-invasive head-out spirometry is a reliable and highly sensitive method to longitudinally assess the course of bacterial lung infections.