AOAC 2019 First Action Methods

(e)

Isolate on an ALOA agar plate at 35 ± 1°C for 24 ± 3 h. The plate should be read after 24 and 48

h (in case there are no typical colonies after 24 h). (f)

The presence of typical colonies confirms a positive result.

(g)

If no typical Listeria colony is identified, repeat steps d and e using 500 µL from the primary

enrichment. J.

Quality Control [External quality control can be performed using one L. monocytogenes strain.] (a) Add one isolated colony from a fresh and pure culture in 10 mL of LPT broth. (b) Mix and incubate at 35 ± 1°C or 37 ± 1°C for 18–24 h. (c) Dilute 1/100 of the culture in LPT broth in order to obtain a suspension containing approximately 10 6 cells/mL of the strain. (d) Follow the protocol from the SAMPLE LYSIS section steps to CONFIRMATION OF POSITIVE RESULTS sections. (e) Check that the results obtained correspond to the characteristics of the tested strains. K. Limitations of the Method The GENE-UP ® Listeria monocytogenes 2 (LMO 2) kit has been evaluated on a large number of matrices. However, given the wide variety of products and manufacturing procedures, it is recommended to check that the composition of the matrices tested does not affect the reliability of GENE-UP ® results.

Reference: J. AOAC Int . (future issue)

Posted: January 2020 (pre-publication)