Nontuberculous mycobacteria (NTM) are emergent pathogens whose importance in human health has been growing. After being regarded mainly as etiological agents of opportunist infections in HIV patients, they have also been recognized as etiological agents of several infections on immune-competent individuals and healthcare-associated infections. The environmental nature of NTM and their ability to assemble biofilms on different surfaces play a key role in their pathogenesis. Here, we review the clinical manifestations attributed to NTM giving particular importance to the role played by biofilm assembly.

Macrophages can potentially kill all mycobacteria by poorly understood mechanisms. In this study, we explore the role of NF-κB in the innate immune response of macrophages against Mycobacterium smegmatis, a nonpathogenic mycobacterium efficiently killed by macrophages, and Mycobacterium avium which survives within macrophages. We show that infection of macrophages with M. smegmatis induces an activation of NF-κB that is essential for maturation of mycobacterial phagosomes and bacterial killing. In contrast, the pathogenic M. avium partially represses NF-κB activation. Using microarray analysis, we identified many lysosomal enzymes and membrane-trafficking regulators, including cathepsins, LAMP-2 and Rab34, were regulated by NF-κB during infection. Our results argue that NF-κB activation increases the synthesis of membrane trafficking molecules, which may be rate limiting for regulating phagolysosome fusion during infection. The direct consequence of NF-κB inhibition is the impaired delivery of lysosomal enzymes to M. smegmatis phagosomes and reduced killing. Thus, the established role of NF-κB in the innate immune response can now be expanded to include regulation of membrane trafficking during infection.

After internalization into macrophages non-pathogenic mycobacteria are killed within phagosomes. Pathogenic mycobacteria can block phagosome maturation and grow inside phagosomes but under some conditions can also be killed by macrophages. Killing mechanisms are poorly understood, although phago-lysosome fusion and nitric oxide (NO) production are implicated. We initiated a systematic analysis addressing how macrophages kill ‘non-pathogenic’Mycobacterium smegmatis. This system was dynamic, involving periods of initial killing, then bacterial multiplication, followed by two additional killing stages. NO synthesis represented the earliest killing factor but its synthesis stopped during the first killing period. Phagosome actin assembly and fusion with late endocytic organelles coincided with the first and last killing phase, while recycling of phagosome content and membrane coincided with bacterial growth. Phagosome acidification and acquisition of the vacuolar (V) ATPase followed a different pattern coincident with later killing phases. Moreover, V-ATPase localized to vesicles distinct from classical late endosomes and lysosomes. Map kinase p38 is a crucial regulator of all processes investigated, except NO synthesis, that facilitated the host for some functions while being usurped by live bacteria for others. A mathematical model argues that periodic high and low cellular killing activity is more effective than is a continuous process.

Both pathogenic and non-pathogenic mycobacteria are internalized into macrophage phagosomes. Whereas the non-pathogenic types are invariably killed by all macrophages, the pathogens generally survive and grow. Here, we addressed the survival, production of nitrogen intermediates (RNI) and intracellular trafficking of the non-pathogenic Mycobacterium smegmatis, the pathogen-like, BCG and the pathogenic M. bovis in different mouse, human and bovine macrophages. The bacteriocidal effects of RNI were restricted for all bacterial species to the early stages of infection. EM analysis showed clearly that all the mycobacteria remained within phagosomes even at late times of infection. The fraction of BCG and M. bovis found in mature phagolysosomes rarely exceeded 10% of total, irrespective of whether bacteria were growing, latent or being killed, with little correlation between the extent of phagosome maturation and the degree of killing. Theoretical modelling of our data identified two different potential sets of explanations that are consistent with our results. The model we favour is one in which a small but significant fraction of BCG is killed in an early phagosome, then maturation of a small fraction of phagosomes with both live and killed bacteria, followed by extremely rapid killing and digestion of the bacteria in phago-lysosomes.

In Europe, the mean incidence of urinary tract infections in intensive care units is 1.1 per 1000 patient‐days. Of these cases, catheter‐associated urinary tract infections (CAUTI) account for 98%. In total, CAUTI in hospitals is estimated to give additional health‐care costs of £1–2.5 billion in the United Kingdom alone. This is in sharp contrast to the low cost of urinary catheters and emphasizes the need for innovative products that reduce the incidence rate of CAUTI. Ureteral stents and other urinary‐tract devices suffer similar problems. Antimicrobial strategies are being developed, however, the evaluation of their efficacy is very challenging. This review aims to provide considerations and recommendations covering all relevant aspects of antimicrobial material testing, including surface characterization, biocompatibility, cytotoxicity, in vitro and in vivo tests, microbial strain selection, and hydrodynamic conditions, all in the perspective of complying to the complex pathology of device‐associated urinary tract infection. The recommendations should be on the basis of standard assays to be developed which would enable comparisons of results obtained in different research labs both in industry and in academia, as well as provide industry and academia with tools to assess the antimicrobial properties for urinary tract devices in a reliable way.

Nontuberculous mycobacteria (NTM) are emergent pathogens whose importance in human health has been gaining relevance after being recognized as etiological agents of opportunist infections in HIV patients. Currently, NTM are recognized as etiological agents of several respiratory and extra-respiratory infections of immune-competent individuals. The environmental nature of NTM together with the ability to assemble biofilms on different surfaces plays a key role on their pathogenesis. In the present work the ability of three fast-growing NTM (Mycobacterium smegmatis, Mycobacterium fortuitum and Mycobacterium chelonae) to persist within a model of human alveolar macrophages was evaluated. Most often human infections with NTM occur by contact with the environment. Biofilms can work as environmental reservoirs. For this reason, it was decided to evaluate the ability of NTM to assemble biofilms on different surfaces. Scanning electron microscopy was used to elucidate the biofilm structure. The ability to assemble biofilms was connected with the ability to spread on solid media known as sliding. Biofilm assembly and intracellular persistence seems to be ruled by different mechanisms.