Biofilm

About: Biofilm is a research topic. Over the lifetime, 23010 publications have been published within this topic receiving 906812 citations. The topic is also known as: biofilms.

Antibiotics as Signal Molecules

Abstract: Antibiotics have been extensively used in the treatment of infectious diseases The lethality of these compounds has been exploited in clinical and laboratory approaches and their specific targets in bacterial physiology elucidated However, along with this development of drugs has come the problem of increasing resistance in microbes, resulting in dramatically reduced therapeutic effectiveness 1 Pathogenic microbes have rapidly evolved efficient mechanisms of resistance, including increased efflux, enzymatic inactivation, target modification, or biofilm formation 2 The concentrations of these molecules required to achieve an antimicrobial effect are likely extremely high compared to the concentrations in which these molecules can be found in natural environments While we know their effect at lethal concentrations, the activities of these molecules at concentrations below the inhibitory limit needs deeper investigation 3 The findings of the nineteenth-century pharmacologist Hugo Schulz, who noted that certain disinfectants could have stimulatory effect on yeast growth at low concentrations, could be considered the first evidence that the action of an antimicrobial can cause a differential response depending on the concentration His observation was the first example of what it would be later called hormesis This term was coined by Chester Southam and John Ehrlich in the mid-1920s and it is used to refer to the ability of certain molecules to induce diverse responses depending on the concentration used 3 The vast amount of information related to the lethal concentration of antibiotics, targets, or side effects, contrasts dramatically with the relatively few studies focused on their effect at concentrations below the MIC (minimal inhibitory concentration) As pointed by Davies, only a small fraction of natural products that have antimicrobial activity have been extensively studied, and their role in natural settings is poorly understood Thus it is possible that many of these molecules formerly considered antibiotics might have a different function in nature It is now believed that many of these compounds might act as signaling molecules that modulate gene expression in microbial populations, or physiological functions such as motility, pigmentation, and production of metabolites, and thus facilitate inter- and intra-species communication 4 This fundamental lack of understanding may be rooted in our conception of the microbial world as single and separated species, as they are usually studied under laboratory conditions However, in nature, each niche is complex, and to different extents, variable in microbial community composition 5,6–8 Therefore it is conceivable that molecules fluctuate in concentration and diversity, thus facilitating communication among species 9 Many interesting lines of research are currently focused on understanding how some antibiotics may affect, either positively or negatively, cell-cell communication systems, and the physiological responses that are affected as a result In some cases, natural products can influence the ability of bacteria to transition from a planktonic state to complex multicellular aggregates attached to surfaces known as biofilms Cells in bioflms are encased in an extracellular matrix which can serve as a barrier for antibiotics 10 One example is the biofilm produced by the gram-negative pathogen, Pseudomonas aeruginosa, which is resistant to antibiotics produced by gram-positive competitors 11 Studies on many model microorganisms from the genera Bacillus, Streptomyces, and Pseudomonas are shedding new light on the fascinating world of cell signaling and communication in microbial world 5,12,13 We will discuss in this review several examples of the dual functions of some well-known antibiotics, including those that when used at sub-inhibitory concentrations (SIC) promote an interesting response in bacterial populations and the ecological implications of such varied responses Also, the role of other naturally synthesized antibiotics will be discussed in the context of cell communication in natural environments, including one of the most exploited environmental niches for antibiotic discovery, the soil

BapA, a large secreted protein required for biofilm formation and host colonization of Salmonella enterica serovar Enteritidis

Abstract: In environmental settings, biofilms represent the common way of life of microorganisms. Salmonella enterica serovar Enteritidis, the most frequent cause of gastroenteritis in developed countries, produces a biofilm whose matrix is mainly composed of curli fimbriae and cellulose. In contrast to other bacterial biofilms, no proteinaceous compound has been reported to participate in the formation of this matrix. Here, we report the discovery of BapA, a large cell-surface protein required for biofilm formation by S. Enteritidis. Deletion of bapA caused the loss of the capacity to form a biofilm whereas the overexpression of a chromosomal copy of bapA increased the biofilm biomass formation. We provide evidence that overproduction of curli fimbriae and not cellulose can compensate for the biofilm deficiency of a bapA mutant strain. BapA is secreted through a type I protein secretion system (BapBCD) situated downstream of the bapA gene and was found to be loosely associated with the cell surface. Experiments with mixed bacterial populations positive or negative for BapA showed that BapA minus cells are not recruited into the biofilm matrix. The expression of bapA is coordinated with that of genes encoding curli fimbriae and cellulose, through the action of csgD. Studies on the contribution of BapA to S. Enteritidis pathogenesis revealed that orally inoculated animals with a bapA-deficient strain survived longer than those inoculated with the wild-type strain. Also, a bapA mutant strain showed a significantly lower colonization rate at the intestinal cell barrier and consequently a decreased efficiency for organ invasion compared with the wild-type strain. Taken together, these data demonstrate that BapA contributes both to biofilm formation and invasion through the regular Salmonella infection route.

The Staphylococcal Biofilm: Adhesins, Regulation, and Host Response.

Abstract: The staphylococci comprise a diverse genus of Gram-positive, nonmotile commensal organisms that inhabit the skin and mucous membranes of humans and other mammals. In general, staphylococci are benign members of the natural flora, but many species have the capacity to be opportunistic pathogens, mainly infecting individuals who have medical device implants or are otherwise immunocompromised. Staphylococcus aureus and Staphylococcus epidermidis are major sources of hospital-acquired infections and are the most common causes of surgical site infections and medical device-associated bloodstream infections. The ability of staphylococci to form biofilms in vivo makes them highly resistant to chemotherapeutics and leads to chronic diseases. These biofilm infections include osteomyelitis, endocarditis, medical device infections, and persistence in the cystic fibrosis lung. Here, we provide a comprehensive analysis of our current understanding of staphylococcal biofilm formation, with an emphasis on adhesins and regulation, while also addressing how staphylococcal biofilms interact with the immune system. On the whole, this review will provide a thorough picture of biofilm formation of the staphylococcus genus and how this mode of growth impacts the host.

Microanatomy at Cellular Resolution and Spatial Order of Physiological Differentiation in a Bacterial Biofilm

Abstract: Bacterial biofilms are highly structured multicellular communities whose formation involves flagella and an extracellular matrix of adhesins, amyloid fibers, and exopolysaccharides. Flagella are produced by still-dividing rod-shaped Escherichia coli cells during postexponential growth when nutrients become suboptimal. Upon entry into stationary phase, however, cells stop producing flagella, become ovoid, and generate amyloid curli fibers. These morphological changes, as well as accompanying global changes in gene expression and cellular physiology, depend on the induction of the stationary-phase sigma subunit of RNA polymerase, σ S (RpoS), the nucleotide second messengers cyclic AMP (cAMP), ppGpp, and cyclic-di-GMP, and a biofilm-controlling transcription factor, CsgD. Using flagella, curli fibers, a CsgD::GFP reporter, and cell morphology as “anatomical” hallmarks in fluorescence and scanning electron microscopy, different physiological zones in macrocolony biofilms of E. coli K-12 can be distinguished at cellular resolution. Small ovoid cells encased in a network of curli fibers form the outer biofilm layer. Inner regions are characterized by heterogeneous CsgD::GFP and curli expression. The bottom zone of the macrocolonies features elongated dividing cells and a tight mesh of entangled flagella, the formation of which requires flagellar motor function. Also, the cells in the outer-rim growth zone produce flagella, which wrap around and tether cells together. Adjacent to this growth zone, small chains and patches of shorter curli-surrounded cells appear side by side with flagellated curli-free cells before curli coverage finally becomes confluent, with essentially all cells in the surface layer being encased in “curli baskets.” IMPORTANCE Heterogeneity or cellular differentiation in biofilms is a commonly accepted concept, but direct evidence at the microscale has been difficult to obtain. Our study reveals the microanatomy and microphysiology of an Escherichia coli macrocolony biofilm at an unprecedented cellular resolution, with physiologically different zones and strata forming as a function of known global regulatory networks that respond to biofilm-intrinsic gradients of nutrient supply. In addition, this study identifies zones of heterogeneous and potentially bistable CsgD and curli expression, shows bacterial curli networks to strikingly resemble Alzheimer plaques, and suggests a new role of flagella as an architectural element in biofilms.