Molecular Insights into Pathogenesis and Infection with Aspergillus Fumigatus

The virulence of fungi is dependent on multiple factors, including the immune status of patients and biological features of fungi. In particular, the virulence of Aspergillus fumigatus is due to the complex interaction among various molecules involved in thermotolerance (such as ribosomal biogenesis proteins, α-mannosyltransferase and heat shock proteins), pigment production (DHN-melanin), immune evasion (like melanin and hydrophobin) and nutrient uptake (such as siderophores and zinc transporters). Other molecules also play important roles in the virulence of A. fumigatus, including cell wall components and those which maintain its integrity (for instance β-1-3 glucan, α-1-3 glucan, chitin, galactomannan and mannoproteins) and adhesion (such as hydrophobins), as well as various hydrolytic enzymes (such as serine and aspartic protease, phospholipases, metalloproteinase and dipeptidyl peptidases). Signalling molecules (including G-protein, cAMP, Ras protein and calcineurin) also increase the virulence through altering the metabolic response to stress conditions and toxins (such as gliotoxin, fumitremorgins, fumagatin and helvolic acid).

Detection of neuraminidase activity in pseudomonas aeruginosa PAO1

Some properties of neuraminidase produced by Pseudomonas aeruginosa PAO1 growth in a defined medium [BHI] were examined and evaluated for its features. The obtained supernatant enzyme of P. aeruginosa PAO1 cultures was used in a sensitive fluorometric assay by using 2'-[4-methylumbelliferyl] alpha-D-N acetylneuraminic acid as substrate.As hydrolyzing MUN with neuraminidase; free N-acetylneuraminic acid and 4-methylumbelliferone were formed with a shift in the fluorescence spectra from 315/374 nm [substrate] to 365/450 nm [product]. Enzyme activity was then measured by the fluorescence of 4-methylumbelliferone at 450 nm. Among the culture media to determine the enzyme production, the highest production of P. aeruginosa PAO1 neuraminidase was found in BHI culture media. Neuraminidase production in P. aeruginosa PAO1 paralleled bacterial growth in defined medium [BHI] and was maximal in the late logarithmic phase of growth but decreased during the stationary phase, probably due to protease production or thermal instability. The neuraminidase of P. aeruginosa PAO1 possessed an optimum temperature of 56 °C and the activity was pH-dependent with maximal activity at pH 5. Heating the enzyme at 56 °C for 45 min in the presence of bovine serum albumin destroyed 33.1% of the activity while the addition of Ca[+2], EDTA and N-acetyl neuraminic acid [NANA] decreased activity markedly. Overall, the results indicated that neuraminidase of P. aeruginosa PAO1 is more an extracellular enzyme than K. pneumonia neuraminidase is