A Simple Sensitive Method for Determining Staphylococcal Thermonuclease in Cheese

Abstract

A simple quantitative method is described for the determination of staphylococcal thermostable nuclease in cheese. The method does not require concentration or purification of the nuclease prior to determination because of the increased sensitivity of the assay (0.5 ng/ml). Assay results of cheddar cheese made from pasteurized milk inoculated with enterotoxin‐A producing Staphylococcus aureus strains demonstrated the sensitivity and reliability of the method for indicating the presence of Staph. aureus at concentrations of ≥ 1.4 × 106/g of cheese.

Staphylococcal growth and enterotoxins (A—D) and thermonuclease synthesis in the presence of dehydrated garlic

“…Thermonuclease activity was determined by the quantitative method of Ibrahim (1981). Before testing, each supernatant fluid was heated in a boiling bath for 15 min and its pH adjusted to 10.…”

The Relationship between S. aureus and Branched-Chain Amino Acids Content in Composite Cow Milk

“…Clotting after incubation at 37 °C between 4–24 h was regarded as a positive result. TNase determination was performed according to the method described by Ibrahim [31]. After an 18-h incubation at 37 °C on Brain Heart Infusion (BHI) broth (Difco, BD Diagnostic Systems, MD), the cultures were put into a water bath at 100 °C for 15 min to eliminate any non-specific heat-labile nuclease activity, and centrifuged at room temperature for 30 min at 3000 rpm before testing.…”

Effect of a novel starter culture and specific ripening conditions on microbiological characteristics of nitrate-free dry-cured pork sausages

“…on de Man, Rogosa, Sharpe (MRS) Agar (Oxoid) acidified to pH 5.5, incubated at 30 C for 72 h under anaerobic conditions (Gas generating kit, Oxoid, BR0038); Enterococci on Slanetz and Bartley (SB) Agar (Oxoid, CM0377), incubated at 37 C for 48 h; Enterobacteriaceae on Violet Red Bile Glucose (VRBG) Agar (Oxoid, CM0485), overlaid with 5 ml of the same medium and incubated at 37 C for 24 h; coliform organisms on Violet Red Bile Lactose (VRBL) Agar (Oxoid, CM0107), overlaid with 5 ml of the same medium and incubated at 30 C for 24 h. For Enterobacteriaceae and coliform organisms, in case of counts below the detection limit as described in the analysis of results section, counts were repeated with the most probable number (MPN) method with brilliant green bile (2%) broth (Oxoid, CM0031 Plasma Fibrinogen (RFP) Agar, all black, convex colonies with an opaque halo were examined under the microscope after Gram staining, and tested for thermonuclease production. Thermonuclease determination was performed according to the method described by Ibrahim (1981).…”