BackgroundThe shiga toxin-producing E. coli (STEC) O104:H4 caused a major outbreak in Germany in spring 2011. STEC are usually susceptible to common antibiotics. However, antibiotic treatment of STEC-infected patients is not recommended because STEC may enhance production and release of shiga toxins (STX) in response to antibiotics, which eventually enhances the frequency and severity of clinical symptoms, including haemolytic uraemic syndrome (HUS) and fatalities.ResultsWe characterized the response to antibiotics of STEC O104:H4 isolates from two HUS patients during the German STEC outbreak in spring 2011 in comparison to the common STEC O157:H7. Liquid cultures of STEC O157:H7 and O104:H4 were incubated with graded dilutions of the antibiotics ciprofloxacin, meropenem, fosfomycin, gentamicin, rifampicin, and chloramphenicol. At defined times of antibiotic treatment, transcriptional activation of the STX2 gene, contents of STX and STX-activity in the culture supernatants were quantified. Unlike the common serotype O157:H7, STEC O104:H4 does not release STX in response to therapeutic concentrations of ciprofloxacin, meropenem, fosfomycin, and chloramphenicol.ConclusionsIn future outbreaks, the response of the respective epidemiologic STEC strain to antibiotics should be rapidly characterized in order to identify antibiotics that do not enhance the release of STX. This will eventually allow clinical studies tackling the question whether antibiotic treatment impacts on the eradication of STEC, clinical course of disease, and frequency of carriers.

Inhibition of phagosome maturation is an important hallmark of mycobacterial pathogenesis. A variety of genomic, transcriptomic and proteomic approaches have been used to pin down the molecule responsible for this pathogenic principle. We in this study characterize a glycolipid of Mycobacterium marinum identified through a screen of mutants disabled in inhibiting phagosome maturation to be phenolphthiocerol diester (phenolic glycolipid, PGL). This molecule is sufficient to impart its ability to inhibit phagosome maturation onto other microbial cells and even inert beads that are used as model pathogens. In addition, it abrogates pro‐inflammatory cytokine secretion induced by strong inducers such as heat‐killed Mycobacterium bovis bacille Calmette–Guérin. This strong dual agonistic effect of PGL overrides pro‐inflammatory and pro‐lysosomal delivery impulses set not only by mycobacteria but also by other pathogens and thus provides convincing evidence that this molecule is a vital mycobacterial virulence factor.

Virulent mycobacteria cause arrest of phagosome maturation as a part of their survival strategy in hosts. This process is mediated through multiple virulence factors, whose molecular nature remains elusive. Using Mycobacterium marinum as a model, we performed a genome-wide screen to identify mutants whose ability to inhibit phagosome maturation was impaired, and we succeeded in isolating a comprehensive set of mutants that were not able to occupy an early endosome-like phagosomal compartment in mammalian macrophages. Categorizing and ordering the multiple mutations according to their gene families demonstrated that the genes modulating the cell envelope are the principal factors in arresting phagosome maturation. In particular, we identified a novel gene, pmiA, which is capable of influencing the constitution of the cell envelope lipids, thereby leading to the phagosome maturation block. The pmiA mutant was not able to resist phagosome maturation and was severely attenuated in mice. Complementing the mutant with the wild-type gene restored the attenuated virulence to wild-type levels in mice.Mycobacterium tuberculosis, the causative agent of tuberculosis, claims the lives of over 1.7 million people per year. An estimated one-third of the world's population is infected with the tuberculosis bacillus (43). The predilection of virulent mycobacteria to dwell in a hostile environment (macrophages) is considered central for effective pathogenesis. The mycobacteria persist inside macrophages by occupying an early endosome-like phagosomal compartment and avoiding the default pathway of phagosome maturation (PM) (3). Phagosomes containing mycobacteria do not have pH values below pH 6.2 and are characterized by the absence of lysosome-associated membrane protein and lysosomal hydrolases, reduced levels of ATPase, and retention of the early endosomal markers Rab5 and TACO or mouse coronin (12,30,40). Phagosomal factors that mediate the killing of mycobacteria at different stages have been described previously (2).Although several host cell mechanisms involved in the inhibition of PM have been proposed, an explanation for how mycobacteria establish a safe haven for themselves in the hostile environment in macrophages remains elusive. Possible roles for mycobacterial urease (17) and lipoarabinomannan in impeding phagosome acidification have been postulated (37). Mycobacterial protein kinase G was shown to prevent transfer of mycobacteria to lysosomes (41). Mycobacterial phosphoinositol mannosides that are similar to the mammalian phosphoinositol lipids enhance fusion of phagosomes containing mycobacteria with early endosomes (39). In addition, Vergne and colleagues identified a secreted mycobacterial lipid phosphatase (SapM) that hydrolyzes phosphoinositol-3-phosphate, leading to inhibition of PM (38). Pathogenic mycobacteria induce disruption of the actin filament network regulated by p38 mitogen-activated protein kinases, but the effector molecules have not been elucidated (2, 18). The close apposition of the mycobacterial...

Hollow mesoporous silica capsules were used as amphiphilic drug delivery vehicles and sustained release systems for antimicrobial and anticancer drugs.

The dynamic interplay between metabolism and immune responses in health and disease, by which different immune cells impact on metabolic processes, are being increasingly appreciated. However, the potential of master regulators of metabolism to control innate immunity are less understood. Here, we studied the cross-talk between leptin signaling and macrophage function in the context of bacterial infections. We found that upon infection with Gram-negative pathogens, such as Salmonella Typhimurium, leptin receptor (Lepr) expression increased in both mouse and human macrophages. Unexpectedly, both genetic Lepr ablation in macrophages and global pharmacologic leptin antagonization augmented lysosomal functions, reduced S. Typhimurium burden, and diminished inflammation in vitro and in vivo. Mechanistically, we show that leptin induction activates the mTORC2/Akt pathway and subsequently down-regulates Phlpp1 phosphatase, allowing for phosphorylated Akt to impair lysosomal-mediated pathogen clearance. These data highlight a link between leptin signaling, the mTORC2/Phlpp1/Akt axis, and lysosomal activity in macrophages and have important therapeutic implications for modulating innate immunity to combat Gram-negative bacterial infections.