Relative cell surface hydrophobicity of Escherichia coli strains with various recognized fimbrial antigens and without recognized fimbriae

Factors Influencing Pseudomonas aeruginosa Initial Adhesion and Evolution at the Dodecane-Water Interface

Bacterial adhesion and evolution at the oil-water interface are important for a broad range of applications such as food manufacturing and microbial-enhanced oil recovery, etc. However, our understanding on bacterial interfacial adhesion and evolution, particularly at the single-cell level, is still far from complete. In this work, by employing Pseudomonas aeruginosa PAO1 at the dodecane-water interface as a model system, we have studied the effects of different factors on bacterial interfacial adhesion and the dynamic evolution of bacterial interfacial behavior at the single-cell level. The results show that PAO1 cells displayed a chemotactic behavior toward dodecane. Among the tested factors, bacterial initial interfacial attachment showed a negative correlation with the secreted cell-surface associated lipopolysaccharide and Psl while a positive correlation with type IV pili. Adding nonbiological surfactant Pluronic F-127, as expected, greatly reduced the cell interfacial adhesion. More importantly, the dynamics analysis of cell attachment/detachment at the dodecane-water interface over a long-time scale revealed a reversible to irreversible attachment transition of cells. This transition is accompanied with the interface aging resulting from bacterial activities, which led to an increase of the interfacial viscoelasticity with time and finally the formation of the gel-like interface. Further analysis demonstrated the important role of exopolysaccharides in the latter process. Our findings provide more details of bacterial oil-water interfacial behavior at the single-cell level and may shed light on developing new strategies for controlling bacterial colonization at the oil-water interface.

Level of Fimbriation Alters the Adhesion of Escherichia coli Bacteria to Interfaces

Adhesion of bacteria to interfaces is the first step in pathogenic infection, in biofilm formation, and in bioremediation of oil spills and other pollutants. Bacteria use a variety of surface structures to promote interfacial adhesion, with the level of expression of these structures varying in response to local conditions and environmental signals. Here, we investigated how overexpression of type 1 fimbriae, one such appendage, modifies the ability of Escherichia coli to adhere to solid substrates, via biofilm formation and yeast agglomeration, and to oil/water interfaces, via a microbial adhesion to hydrocarbon assay. A plasmid that enables inducible expression of E. coli MG1655 type 1 fimbriae was transformed into fimbriae-deficient mutant strain MG1655ΔfimA. The level of fimH gene expression in the engineered strain, measured using quantitative real-time PCR, could be tuned by changing the concentration of inducer isopropyl β-d-1-thiogalactopyranoside (IPTG), and was higher than that in strain MG1655. Increasing the degree of fimbriation only slightly modified the surface energy and zeta potential of the bacteria, but enhanced their ability to agglomerate yeast cells and to adhere to solid substrates (as measured by biofilm formation) and to oil/water interfaces. We anticipate that the tunable extent of fimbriation accessible with this engineered strain can be used to investigate how adhesin expression modifies the ability of bacteria to adhere to interfaces and to actively self-assemble there.

Surface and virulence properties of environmental Vibrio cholerae non-O1 from Albufera Lake (Valencia, Spain)

A total of 140 environmental Vibrio cholerae non-O1 isolates, together with several culture collection strains from both environmental and clinical sources, were studied in relation to hemagglutination, surface hydrophobicity, and the enzymatic, hemolytic, cytotoxic, and enterotoxic activities of their extracellular products. A total of 78 and 62% of the strains produced hemagglutinins and exohemagglutinins, respectively. Four different hemagglutinating and two exohemagglutinating activities were found by using eight sugars in the inhibition assays. Cell-bound mannose-sensitive hemagglutination was detected mainly in chicken blood, whereas fucose-sensitive hemagglutination was recorded only in human blood. Cell-bound hemagglutinin resistant to all sugars tested was the only one related to surface hydrophobicity. The surface properties varied along the growth curves. The non-O1 strains displayed strong enzymatic and hemolytic activities, except for esculin hydrolysis. Of 26 non-O1 isolates selected for cytotoxin and enterotoxin production, 23 showed a wide spectrum of cytotoxic effects on cell lines of poikilothermic and homoiothermic species, but they were weakly enterotoxigenic in the infant mouse test. All extracellular products of cytotoxic strains were proteolytic, lipolytic, and hemolytic, and a high percentage produced hemagglutination of chicken blood. The cytotoxic factors in the non-O1 strains analyzed were not R plasmid mediated.

The effect of subinhibitory concentrations of some antibiotics on the hydrophobicity of gram-negative bacteria

Cell surface hydrophobicity is currently regarded as an important factor in promoting bacterial adherence to a wide variety of surfaces. This feature was investigated in some Gram-negative bacteria isolated from urinary tract infections and the extent to which their surface characteristics were affected by subinhibitory concentrations of some antibiotics was assayed. Surface properties were evaluated using the salting-out technique (SAT) and bacterial absorption to n-hexadecane (BATH). SAT showed that all except 3 Escherichia coli strains were autoaggregating. BATH detected more hydrophobic characteristics in the stationary phase of bacterial growth. Pretreatment with antibiotics generally reduced hydrophobicity and thus affected the initial reversible phase of attachment of bacteria to eukaryotic cells.

Hemagglutinating properties of Shigella dysenteriae type 1 and other Shigella species

Strains of Shigella dysenteriae type 1 cultured in Casamino Acids-yeast extract broth medium in the presence of 1 mM calcium chloride at 37 degrees C for 22 h induced hemagglutination of erythrocytes that was inhibited by N-acetylneuraminic acid, N-acetylneuramin-lactose, and alpha 1-glycoprotein. The hemagglutination was heat labile, and the absence of cell-surface appendages suggested a nonfimbrial adhesin(s). Under the same conditions, strains of Shigella flexneri (types 1a, 1b, 2a, and 2b) showed N-acetylneuraminic acid-resistant hemagglutination of erythrocytes.