Ferric Ammonium Citrate Supplement

Description

For this reason this supplement is added to Listeria Enrichment Broth Base in order to obtain Fraser Broth or Half Fraser Broth.

This medium is also supplemented with specific antibiotics.

In the complete medium any darkening of the medium can be taken as presumptive presence of Listeria, because at the same time the growth of enterococci, which are also able to hydrolyze esculin, is suppressed by the inclusion of lithium chloride and the companion flora is inhibited by nalidixic acid and acriflavine hydrochloride.

Technique

Collect, dilute and prepare samples and volumes as required according to specifications, directives, official standard regulations and/or expected results.

Reconstitute the vial with 6 mL of sterile diluent in aseptic conditions and add it to 500 mL of sterilized Listeria Enrichment Broth Base cooled to 50 °C; add also the selective agent in order to inhibit the companion flora.

Pour the complete medium into tubes and inoculate.

Incubate the tubes in aerobic atmosphere at 35 ± 2 °C for 24-48 h.

Incubation times longer than those mentioned above or different incubation temperatures may be required depending on the sample or the specifications.

After incubation, inoculate the positive cultures / dark tubes by streaking on any secondary recommended culture medium to confirm Listeria isolation.

The presumptive presence of Listeria spp. must be confirmed by further microbiological and biochemical tests.

Reconstitute the original freeze-dried vial by adding 6 mL of sterile distilled water.

Note: each vial is sufficient to supplement 500 mL of medium base: Fraser Broth.

Physical/chemical control

Microbiological control

Reconstitute 1 vial as indicated in Composition; shake and dissolve completely.

Add the supplement into Fraser Broth Base, for functionality testing.

Analytical methodology according to ISO 11133:2014/Amd 1:2018; A2:2020.

Aerobiosis. Incubation at 37 ± 1 °C, reading after 24/44 ± 4 h.

Sterility control

Add 5 mL of the sample to 100 mL of TSB and to 100 mL of Thioglycollate.

Incubation 48 hours at 30-35 °C and 48 hours at 20-25 °C: NO GROWTH.

Check at 7 days after incubation in same conditions.

• ATLAS, R.M. (1993) Handbook of Microbiological Media. CRC Press. Boca Raton. Florida.
• FRASER, J.A. & W.H. SPERBER (1988) Rapid detection of Listeria spp. in food and environmental samples by esculin hydrolysis. J. Food Prot. 51:762-765.
• ISO 11133:2014/Amd 1:2018. Microbiology of food, animal feed and water. Preparation, production, storage and performance testing of culture media.
• ISO 11290-1:2017 Standard. Microbiology of the food chain. Horizontal method for the detection and enumeration of Listeria monocytogenes and for Listeria spp. - Part 1: Detection Method.
• ISO 11290-2:2017 Standard. Microbiology of the food chain. Horizontal method for the detection and enumeration of Listeria monocytogenes and for Listeria spp. - Part 2: Enumeration Method.
• McCLAIN, D. & W.H. LEE (1988) Development of a USDA-FSIS method for isolation of Listeria monocytogenes from raw meat and poultry. J. AOAC 71:660-664.
• VANDERZANT, C & D.F. SPLITTSTOESSER (1992) Compendium of methods for the microbiological examination of foods. APHA. Washington. DC.