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Chromophore-binding domains from plant and bacterial photoreceptor proteins have recently gathered increasing attention as new sources of genetically encoded fluorescent proteins (FPs). In particular, FPs based on the flavin-binding LOV (light, oxygen, or voltage sensing) domain offer advantages over green fluorescent protein (GFP) owing to their smaller size, pH and thermal stability, utility under anaerobic conditions and their ability to generate reactive oxygen species. This review focuses on the potential applications of this emerging class of fluorescent reporters, discusses the advantages and limitations of LOV-based FPs, whilst offering insights regarding the further development of this technology for bioimaging and photodynamic therapy., (Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Nosocomial infections are increasingly being recognised as a major patient safety issue. The modern hospital environment and associated health care practices have provided a niche for the rapid evolution of microbial pathogens that are well adapted to surviving and proliferating in this setting, after which they can infect susceptible patients. This is clearly the case for bacterial pathogens such as Methicillin Resistant Staphylococcus aureus (MRSA) and Vancomycin Resistant Enterococcus (VRE) species, both of which have acquired resistance to antimicrobial agents as well as enhanced survival and virulence properties that present serious therapeutic dilemmas for treating physicians. It has recently become apparent that the spore-forming bacterium Clostridium difficile also falls within this category. Since 2000, there has been a striking increase in C. difficile nosocomial infections worldwide, predominantly due to the emergence of epidemic or hypervirulent isolates that appear to possess extended antibiotic resistance and virulence properties. Various hypotheses have been proposed for the emergence of these strains, and for their persistence and increased virulence, but supportive experimental data are lacking. Here we describe a genetic approach using isogenic strains to identify a factor linked to the development of hypervirulence in C. difficile. This study provides evidence that a naturally occurring mutation in a negative regulator of toxin production, the anti-sigma factor TcdC, is an important factor in the development of hypervirulence in epidemic C. difficile isolates, presumably because the mutation leads to significantly increased toxin production, a contentious hypothesis until now. These results have important implications for C. difficile pathogenesis and virulence since they suggest that strains carrying a similar mutation have the inherent potential to develop a hypervirulent phenotype.

The ability of an isogenic set of mutants of Salmonella enterica serovar Typhimurium L354 (SL1344) with defined deletions in genes encoding components of tripartite efflux pumps, including acrB, acrD, acrF and tolC, to colonize chickens was determined in competition with L354. In addition, the ability of L354 and each mutant to adhere to, and invade, human embryonic intestine cells and mouse monocyte macrophages was determined in vitro. The tolC and acrB knockout mutants were hyper-susceptible to a range of antibiotics, dyes and detergents; the tolC mutant was also more susceptible to acid pH and bile and grew more slowly than L354. Complementation of either gene ablated the phenotype. The tolC mutant poorly adhered to both cell types in vitro and was unable to invade macrophages. The acrB mutant adhered, but did not invade macrophages. In vivo, both the acrB mutant and the tolC mutant colonized poorly and did not persist in the avian gut, whereas the acrD and acrF mutant colonized and persisted as well as L354. These data indicate that the AcrAB-TolC system is important for the colonization of chickens by S. Typhimurium and that this system has a role in mediating adherence and uptake into target host cells.