Cortical cell stiffness is independent of substrate mechanics

Cortical stiffness is an important cellular property that changes during migration, adhesion and growth. Previous atomic force microscopy (AFM) indentation measurements of cells cultured on deformable substrates have suggested that cells adapt their stiffness to that of their surroundings. Here we show that the force applied by AFM to a cell results in a significant deformation of the underlying substrate if this substrate is softer than the cell. This ‘soft substrate effect’ leads to an underestimation of a cell’s elastic modulus when analysing data using a standard Hertz model, as confirmed by finite element modelling and AFM measurements of calibrated polyacrylamide beads, microglial cells and fibroblasts. To account for this substrate deformation, we developed a ‘composite cell–substrate model’. Correcting for the substrate indentation revealed that cortical cell stiffness is largely independent of substrate mechanics, which has major implications for our interpretation of many physiological and pathological processes

Chemical composition of the extracellular slime glycolipoprotein of Pseudomonas aeruginosa and its relation to gentamicin resistance

The slime glycolipoproteins (GLPs) extracted from Pseudomonas aeruginosa strain C2 and its laboratory-induced gentamicin-resistant variant were analysed for cross chemical composition. The GLP of the wild-type strain contained significantly greater amounts of neutral sugars, uronic acid and thiobarbituric-reactive material (p < 0.001) than the GLP of the gentamicin-resistant variant. Also significantly higher (p < 0.01) was the amino-sugar content of the GLP from the wild-type strain. Paper chromatographic analyses of the hydrolysates of the GLPs revealed that two neutral sugars, rhamnose and mannose, were absent from the GLP of the resistant variant. The GLP of strain C2 contained significantly less protein than the GLP of the gentamicin-resistant variant

Staphylococci from the feces of different animal species: biotypes of Staphylococcus aureus strains of sheep and goat origin

Staphylococcus aureus was found in 96% of the rectal swabs from 133 sheep and in 80% of the swabs from 125 goats. Seventy seven percent of the isolates from both hosts exhibited the fibrinolytic and growth characteristics of human biotype A on human plasma and crystal violet agar, respectively, but 99% of these isolates resembled S. aureus of animal origin in their other properties. Only 21% of the sheep and 24% of the goat isolates were clearly identifiable as human biotype A and animal biotypes B and C