Agar Test pH 7.2 Cat Nº: AG-2023
Standard Dehydrated Culture Media medium for the detection of antimicrobial inhibitors in meat and organ samples
Formula in g/l
Final pH 7.2 ± 0.2 at 25ºC
Suspend 25.8 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121ºC for 15 minutes. Cool to 45-50ºC and aseptically add a spore suspension of Bacillus subtilis (BGA) containing approximately 1×107 CFU/ml (final concentration in mediim 1×104 cfu/ml). Pour into plates. The prepared medium should be used inmediatelly. The color is amber.
The dehydrated medium should be homogeneous, free-flowing and beige in color. If there are any physical changes, discard the medium.
AGAR TEST pH 6.0 in combination with Agar test pH 7.2 and 8.0 is used for the detection of antimicrobial inhibitors in meat and organ samples.
Prepare meat samples by cutting 2mm thick slices of tissue 8 mm in diameter. A total of 6 discs are required for the complete 3-plate test (Test Agar pH 6.0, pH 7.2 Cat. Nº 2023 and pH 8.0 Cat. Nº2024). Using sterile forceps, place two of the discs in diametrically opposite positions on each test plate. Aseptically place appropriate control disc on each of the three plates.
Antimicrobial inhibitors contained in the samples diffuse into the nutrient media and cause growth-free inhibition zones to develop on the otherwise thickly covered plates. Repeated tests with pH 6.0, pH 8.0 and pH 7.2 are necessary, as penicillin and streptomycin are optimally active at pH 6.0 and 8.0 respectively and the activity optimum of sulfonamide is found at pH 7.2. Addition of trimethoprim to Test Agar pH 7.2 considerably increases the sensitivity of the test system to sulfonamides.
Incubate the plates at 30ºC during 18-24 hours. Complete inhibition of growth with a zone of inhibition of at least 2 mm is considered as a positive result. An inhibitory zone of 1-2 mm must be regarded as questionable. This only applies if the controls, prepared at the same time show inhibition zones measuring about 6 mm.
The following results were obtained in the performance of the medium from type cultures after incubation at a temperature of 30 and observed after 18 – 24 hours
Bacillus subtilis (BGA) (DSZM 618)
Arbeitsgruppe des Instituts für Lebensmitteltechnologie und Verpackung der Technischen Universität München: Merkblätter für die Prüfung von Pack-mitteln, Merkblatt 18 "Prüfung auf antimikrobielle Bestandteile in Pack-stoffen". – Verpackgs.-Rdsch., 25; Techn.-wiss. Beilagen; 5-8 (1974).
Once opened keep powdered medium closed to avoid hydration.