GB 4789.4-2024 National food safety standard - Food microbiological examination - Salmonella
1 Scope
This standard specifies an examination method for Salmonella in food.
This standard is applicable to the examination of Salmonella in food.
2 Equipment and materials
In addition to the conventional sterilization and culture equipment in microbiological laboratory, other equipment and materials required are as follows.
2.1 Refrigerator: 2℃~8℃.
2.2 Constant temperature incubator: 36℃±1℃, complete with thermostats of 42℃±1℃ and 48℃±2℃.
2.3 Homogenizer.
2.4 Oscillator.
2.5 Balance: With a sensitivity of 0.1g.
2.6 Aseptic conical flasks: 500mL and 250mL.
2.7 Aseptic measuring cylinder: 50mL.
2.8 Aseptic homogenizing cup and bag.
2.9 Aseptic wide-mouth bottle: 500mL.
2.10 Aseptic pipettes: 1mL (with scale division of 0.01mL) and 10mL (with scale division of 0.1mL), or micropipettor and sucker.
2.11 Aseptic culture dishes: With diameters of 60mm and 90mm, respectively.
2.12 Aseptic test tubes: 10mm×75mm, 15mm×150mm, 18mm×180mm or other suitable specifications.
2.13 Aseptic small glass tube: 3mm×50mm.
2.14 Aseptic inoculation loops: 10μL (about 3mm in diameter) and 1μL, complete with inoculation needle.
2.15 pH meter or precision pH test paper.
2.16 Microbial biochemical identification system.
2.17 Biological safety cabinet.
3 Culture media and reagents
3.1 Buffered peptone water (BPW): See A.1.
3.2 Tetrathionate broth base (TTB): See A.2.
3.3 Rappaport-vassiliadis soya (RVS) peptone broth: See A.3.
3.4 Bismuth sulfite (BS) agar: See A.4.
3.5 Hektoen enteric (HE) agar: See A.5.
3.6 Xylose lysine desoxycholoate (XLD) agar: See A.6.
3.7 Triple sugar iron (TSI) agar: See A.7.
3.8 Nutrient agar (NA): See A.8.
3.9 Semi-solid agar: See A.9.
3.10 Peptone water and indole reagents: See A.10.
3.11 Urea agar (pH 7.2): See A.11.
3.12 Potassium cyanide (KCN) medium: See A.12.
3.13 Lysine decarboxylase test medium: See A.13.
3.14 Sugar fermentation medium: See A.14.
3.15 O-nitrophenyl β-D-galactopyranoside (ONPG) medium: See A.15.
3.16 Sodium malonate medium: See A.16.
3.17 Salmonella chromogenic medium.
3.18 Salmonella diagnostic serum.
3.19 Biochemical identification kit.
4 Examination procedures
See Figure 1 for the examination procedures of Salmonella.
5 Operation steps
5.1 Pre-enrichment
Aseptically take 25g(mL) of the sample, and put it into an aseptic homogenizing cup containing 225mL of BPW and homogenize it at 8,000r/min~10,000r/min for 1min~2min, or put it into an aseptic homogenizing bag containing 225mL of BPW and pat the bag for 1min~2min with a pat type homogenizer. In case of liquid sample, it is allowed to shake and mix the sample in an aseptic conical flask or another suitable container that contains 225mL of BPW. If it is necessary to adjust the pH value of the sample, adjust the pH value to 6.8±0.2 with 1mol/L NaOH or HCl. Aseptically transfer the sample into a 500-mL conical flask or another suitable container (if the homogenizing cup itself has a non-porous cover or if a homogenizing bag is used, the sample may not be transferred), and then culture it at 36℃±1℃ for 8h~18h.
In case of milk powder, aseptically weigh 25g of the sample, and slowly pour it onto the liquid surface of 225mL of BPW in a wide-mouth bottle or homogenizing bag, without adjusting the pH value or mixing it evenly. Keep it still at room temperature for 60min±5min, then mix it evenly, and culture it at 36℃±1℃ for 16h~18h.
Foreword I
1 Scope
2 Equipment and materials
3 Culture media and reagents
4 Examination procedures
5 Operation steps
6 Results and report
Annex A Culture media and reagents
Annex B Common Salmonella antigens
