Rapid Detection of Excessive CFU Counts of Enterobacteriaceae, S. aureus and Yeasts by Nitrate Reduction/Glucose Dissimilation (NGD) Monitoring in Selective Media

Abstract

A technique was developed for the approximate selective estimation of CFU loads of thermotrophic Enterobacteriaceae and S. aureus in foods and meals, relying on rate of nitrate reduction and glucose dissimilation (NGD test) in lauryl sulfate nitrate glucose broth and modified liquid Baird Parker medium with nitrate and glucose added, respectively, both incubated at 42.5"C. Yeast CFU could be assessed similarly in oxytetracyclin gentamicin glucose broth at 30°C. The fate of nitrate and glucose was monitored by urinanalysis dip sticks. Response times were 7 and 2 hr for CFU levels of IO5 and 10s g-', respectively, allowing feedback to production lines within one working day. The procedure requiring no other instrumentation than a centrifuge, also has been applied successfully as a field test procedure.

Near on-line detection of enteric bacteria using lux recombinant bacteriophage

“…This method, however, takes some 24 hs to complete and although it decreases the time for identification, interpretation of the curves within the laboratory situation may be difficult. Van Netten et al [7] investigated the rapid detection of excessive counts of Enterobacteriaceae by nitrate reduction/glucose dissimilation monitoring in selective media. The test gave detection times of no more than 7 h but that is still relatively incompatible with HACCP.…”