Formulations and process for isolating viable microorganisms from positive blood cultures

A buffer for isolating and concentrating viable microorganisms from a positive blood culture sample consisting of:

• a nutrient base solution;
• at least one non-ionic detergent;
• optionally, ammonium chloride;
• and
• at least one thiol, wherein the relative amounts of the nutrient base solution, the at least one non-ionic detergent, and the at least one thiol in the buffer are selected to preserve the viability of S. pneumoniae,
• wherein the nutrient base solution consists of casein peptone at a concentration in the buffer of about 8 g/L to about 35 g/L, sodium chloride at a concentration in the buffer of about 2 g/L to about 10 g/L, soy peptone at a concentration in the buffer of about 1.5 g/L to about 15 g/L, and potassium phosphate at a concentration in the buffer of about 0.5 g/L to about 5 g/L and optionally at least one other nutrient;
• the at least one thiol consisting of L-cysteine at a concentration in the buffer of about 0.01 g/L to about 2.5 g/L and sodium thioglycolate at a concentration in the buffer of about 0.01 g/L to about 2.5 g/L;
• and
• the at least one non-ionic detergent consisting of saponin at a concentration in the buffer of about 0.01 g/L to about 10 g/L and polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether at a concentration in the buffer of 0.335 g/L.