Antibiotic resistance is a massive and serious threat to human welfare and healthcare. Apart from being genetically resistant to antibiotics, the other important mechanism by which bacteria can evade antibiotics is multidrug tolerance. Here cells enter into a transiently nongrowing phase, and as a result, latent infection remains inside the host, causing disease recurrence. Biofilm-derived antibiotic tolerance and persister formation of the pathogenic bacteria inside the host remain a serious issue of treatment failure and recurrent chronic infection in the case of all major pathogens. As a result, new chemotherapeutic agents are sought that specifically inhibit biofilm formation or maturation as well as cause the dispersion of mature biofilms, thus allowing the conventional drugs to kill sensitive cells residing inside. This mini-review attempts to analyze different small-molecule-based chemical approaches that have been used to enable bacterial biofilm inhibition at different steps of maturation.
Bacterial populations can use bet-hedging strategies to cope with rapidly changing environments. One example is non-growing cells in clonal bacterial populations that are able to persist antibiotic treatment. Previous studies suggest that persisters arise in bacterial populations either stochastically through variation in levels of global signalling molecules between individual cells, or in response to various stresses. Here, we show that toxins used in contact-dependent growth inhibition (CDI) create persisters upon direct contact with cells lacking sufficient levels of CdiI immunity protein, which would otherwise bind to and neutralize toxin activity. CDI-mediated persisters form through a feedforward cycle where the toxic activity of the CdiA toxin increases cellular (p)ppGpp levels, which results in Lon-mediated degradation of the immunity protein and more free toxin. Thus, CDI systems mediate a population density-dependent bet-hedging strategy, where the fraction of non-growing cells is increased only when there are many cells of the same genotype. This may be one of the mechanisms of how CDI systems increase the fitness of their hosts.
The Impact of Skilled Foreign Workers on Firms: An Investigation of Publicly Traded U.S. Firms * Many U.S. businessmen are vocally in favor of an increase in the number of H-1B visas. Is there systematic evidence that this would positively affect firms' productivity, sales, employment or profits? To address these questions we assemble a unique dataset that matches all labor condition applications (LCAs) -the first step towards H-1B visas for skilled foreign-born workers in the U.S. -with firm-level data on publicly traded U.S. firms (from Compustat). Our identification is based on the sharp reduction in the annual H-1B cap that took place in 2004, combined with information on the degree of dependency on H-1B visas at the firm level as in Kerr and Lincoln (2010). The main result of this paper is that if the cap on H-1B visas were relaxed, a subset of firms would experience gains in average labor productivity, firm size, and profits. These are firms that conduct R&D and are heavy users of H-1B workers -they belong to the top quintile among filers of LCAs. These empirical findings are consistent with a heterogeneous-firms model where innovation enhances productivity and is subject to fixed costs.
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