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Neuraminidase activity in middle ear effusions
Abstract:
Analyses of Streptococcus pneumoniae culture filtrates and middle ear effusions (MEE) containing S pneumoniae for various hydrolytic enzymes have demonstrated substantial levels of neuraminidase activity when measured employing a sensitive fluorometric assay. S pneumoniae neuraminidase exhibits optimum activity near neutral pH (6.0 to 6.5), and catalyzes the cleavage of sialic acid residues from glycoproteins, gangliosides and mucopolysaccharides. S pneumoniae begins secreting large amounts of neutral neuraminidase (mean [means] = 43.3 units/mL culture filtrate) when cells enter the stationary phase. Nearly all (96%) human chronic MEEs yielding positive cultures for S pneumoniae contain neuraminidase activity (means = 0.200 units/mg protein), while only 21.1% to 45.5% of all other effusions contain the enzyme. Middle ear effusions obtained from S pneumoniae infected-chinchillas contained large amounts of neuraminidase activity (approximately 200 units/mL), which decayed exponentially in vivo with an apparent half-life of 8 1/2 days. Three neuraminidase isoenzymes (designated I-III) were identified in S pneumoniae culture filtrates, as well as in MEEs from chinchillas infected with the organism, using a combination of ion-exchange and gel filtration chromatography. With 4-methylumbelliferyl-N-acetylneuraminic acid serving as substrate, preparation I from both culture filtrates and MEEs was characterized by a high Michaelis constant (Km), while forms II and III had low Km values. Preferred substrates were orosomucoid and neuramin-lactose; gangliosides, thyroglobulin, and bovine submaxillary mucin were poorer substrates.
Insights
Streptococcus pneumoniae produces significant neuraminidase, an enzyme crucial for cleaving sialic acid. This enzyme is abundant in middle ear infections and shows distinct isoenzyme properties.
Area of Science:
- Microbiology
- Enzymology
Background:
- Streptococcus pneumoniae is a common cause of bacterial infections, including otitis media.
- Neuraminidase enzymes play a role in bacterial pathogenesis by modifying host tissues.
Purpose of the Study:
- To characterize the neuraminidase activity in Streptococcus pneumoniae.
- To investigate the presence and properties of neuraminidase in middle ear effusions (MEE).
Main Methods:
- Fluorometric assays were used to measure neuraminidase activity.
- Ion-exchange and gel filtration chromatography were employed to isolate and identify enzyme isoenzymes.
- Kinetic parameters (Km) were determined using various substrates.
Main Results:
- Substantial neutral neuraminidase activity was detected in S. pneumoniae culture filtrates and MEEs.
- Neuraminidase was present in 96% of human chronic MEEs with S. pneumoniae.
- Three distinct neuraminidase isoenzymes (I-III) were identified, with varying kinetic properties.
Conclusions:
- Streptococcus pneumoniae secretes significant amounts of neuraminidase, particularly during the stationary phase.
- Neuraminidase activity is a common feature of S. pneumoniae-associated middle ear infections.
- The identified neuraminidase isoenzymes exhibit differential substrate specificities and kinetic properties.