The influence of microorganisms growing as sessile communities in a large number of human infections has been extensively studied and recognized for 30–40 years, therefore warranting intense scientific and medical research. Nonetheless, mimicking the biofilm-life style of bacteria and biofilm-related infections has been an arduous task. Models used to study biofilms range from simple in vitro to complex in vivo models of tissues or device-related infections. These different models have progressively contributed to the current knowledge of biofilm physiology within the host context. While far from a complete understanding of the multiple elements controlling the dynamic interactions between the host and biofilms, we are nowadays witnessing the emergence of promising preventive or curative strategies to fight biofilm-related infections. This review undertakes a comprehensive analysis of the literature from a historic perspective commenting on the contribution of the different models and discussing future venues and new approaches that can be merged with more traditional techniques in order to model biofilm-infections and efficiently fight them.

SummaryPaired two-component regulatory systems consisting of a sensor kinase and a response regulator are the major means by which bacteria sense and respond to different stimuli. The role of essential response regulator, MtrA, in Mycobacterium tuberculosis proliferation is unknown. We showed that elevating the intracellular levels of MtrA prevented M. tuberculosis from multiplying in macrophages, mice lungs and spleens, but did not affect its growth in broth. Intracellular trafficking analysis revealed that a vast majority of MtrA overproducing merodiploids were associated with lysosomal associated membrane protein (LAMP-1) positive vacuoles, indicating that intracellular growth attenuation is, in part, due to an impaired ability to block phagosome-lysosome fusion. A merodiploid strain producing elevated levels of phosphorylation-defective MtrA (MtrA D53N ) was partially replicative in macrophages, but was attenuated in mice. Quantitative real-time PCR analyses revealed that expression of dna A, an essential replication gene, was sharply upregulated during intramacrophage growth in the MtrA overproducer in a phosphorylation-dependent manner. Chromatin immunoprecipitation using anti-MtrA antibodies provided direct evidence that MtrA regulator binds to dna A promoter in vivo indicating that dna A promoter is a MtrA target. Simultaneous overexpression of mtr A regulator and its cognate mtr B kinase neither inhibited growth nor sharply increased the expression levels of dna A in macrophages. We propose that proliferation of M. tuberculosis in vivo depends, in part, on the optimal ratio of phosphorylated to nonphosphorylated MtrA response regulator.

SummaryThe genetic factors responsible for the regulation of cell division in Mycobacterium tuberculosis are largely unknown. We showed that exposure of M. tuberculosis to DNA damaging agents, or to cephalexin, or growth of M. tuberculosis in macrophages increased cell length and sharply elevated the expression of Rv2719c, a LexA-controlled gene. Overexpression of Rv2719c in the absence of DNA damage or of antibiotic treatment also led to filamentation and reduction in viability both in broth and in macrophages indicating a correlation between Rv2719c levels and cell division. Overproduction of Rv2719c compromised midcell localization of FtsZ rings, but had no effect on the intracellular levels of FtsZ. In vitro, the Rv2719c protein did not interfere with the GTPdependent polymerization activity of FtsZ indicating that the effects of Rv2719c on Z-ring assembly are indirect. Rv2719c protein exhibited mycobacterial murein hydrolase activity that was localized to the N-terminal 110 amino acids. Visualization of nascent peptidoglycan (PG) synthesis zones by probing with fluoresceinated vancomycin (Van-FL) and localization of green fluorescent protein-Rv2719c fusion suggested that the Rv2719c activity is targeted to potential PG synthesis zones. We propose that Rv2719c is a potential regulator of M. tuberculosis cell division and that its levels, and possibly activities, are modulated under a variety of growth conditions including growth in vivo and during DNA damage, so that the assembly of FtsZ-rings, and therefore the cell division, can proceed in a regulated manner.

FtsZ, a bacterial homolog of tubulin, forms a structural element called the FtsZ ring (Z ring) at the predivisional midcell site and sets up a scaffold for the assembly of other cell division proteins. The genetic aspects of FtsZ-catalyzed cell division and its assembly dynamics in Mycobacterium tuberculosis are unknown. Here, with an M. tuberculosis strain containing FtsZ TB tagged with green fluorescent protein as the sole source of FtsZ, we examined FtsZ structures under various growth conditions. We found that midcell Z rings are present in approximately 11% of actively growing cells, suggesting that the low frequency of Z rings is reflective of their slow growth rate. Next, we showed that SRI-3072, a reported FtsZ TB inhibitor, disrupted Z-ring assembly and inhibited cell division and growth of M. tuberculosis. We also showed that M. tuberculosis cells grown in macrophages are filamentous and that only a small fraction had midcell Z rings. The majority of filamentous cells contained nonring, spiral-like FtsZ structures along their entire length. The levels of FtsZ in bacteria grown in macrophages or in broth were comparable, suggesting that Z-ring formation at midcell sites was compromised during intracellular growth. Our results suggest that the intraphagosomal milieu alters the expression of M. tuberculosis genes affecting Z-ring formation and thereby cell division.Mycobacterium tuberculosis, the causative agent of tuberculosis, is an important infectious agent that globally causes more than three million new infections each year (8). Recent years have seen an increase in the number of M. tuberculosis strains that are resistant to one or more antituberculosis drugs, and this has highlighted the need for the development of a new generation of antimicrobial agents. One hallmark of the M. tuberculosis life cycle is that it exists in two metabolically distinct growth states: an active replicative state and a nonproliferative persistent state where the bacterium survives without any increase in the bacterial burden on the host. Physiological studies carried out by Wayne and colleagues indicate that M. tuberculosis cells in the hypoxiainduced nonreplicative persistent state are blocked at the cell division stage after completing DNA replication and undergo a round of cell division prior to initiation of a new round of DNA replication (40,41). This latter process is also referred to as reactivation. Development of antimycobacterial agents targeting the cell division process could potentially prevent the multiplication and subsequent proliferation of the pathogen in active, as well as reactivation, growth states.FtsZ, a bacterial homolog of tubulin, is a key player in cell division and is essential for initiation of this process (22, 32). FtsZ protein catalyzes the formation of distinct structures, referred to as FtsZ rings (Z rings), at the midcell site and sets up a scaffold for ordered assembly of other cell division proteins. The combined action of multiple cell division proteins results in septation (22,32)....

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