Food Microbiological Examination: Enumeration of Coliforms

Transcription

1 Translated English of Chinese Standard: GB Translated by: Wayne Zheng et al. NATIONAL STANDARD GB OF THE PEOPLE S REPUBLIC OF CHINA GB National Food Safety Standard Food Microbiological Examination: Enumeration of Coliforms Issued on: March 26, 2010 Implemented on: June, 1, 2010 Issued by: Ministry of Health of the People s Republic of China Page 1 of 17

2 Tips - GB 4789 Series (Not part of this Standard) Standard ID GB GB Standard Name examination: General guidelines examination: Aerobic plate count Issued Date Enforced Date New Version (Click to check)? GB GB GB GB/T GB/T GB/T GB/T GB GB/T GB/T examination: Enumeration of coliforms examination: Salmonella National Food Safety Standard Microbiological Examination of Food Hygiene - Examination of Shigella diarrheogenic Escherichia coli Vibrio parahaemolyticus Yersinia enterocolitica Campylobacter jejuni examination: Staphylococcus aureus streptococcus hemolyticus Clostridium botulinum and botulinus toxin Page 2 of 17

3 GB GB/T GB National Food Safety Standard Microbiological Examination of Food Hygiene - Examination of Clostridium Perfringens Bacillus cereus examination: Enumeration of moulds and yeasts GB/T GB/T GB GB/T GB/T GB/T GB/T GB/T GB/T GB/T Microbiological examination of food hygiene Identification of common mycotoxin producing fungi meat and meat products examination: Milk and milk products egg and egg products aquatic product foods frozen drinks and cold drinks flavourings cold dish and bean products candy, cake and preserved fruits wines Page 3 of 17

4 GB/T commercial sterilization of canned food GB/T residue of antibiotics in fresh milk GB/T Microbiological examination of food hygiene Staining methods, culture mediums and reagents GB/T pseudomonas cocovenenans subsp. farinofermentans GB examination: Listeria monocytogenes GB/T GB/T GB/T GB salmonellae, shigellae, and diarrhoea causative Escherichia coli by means of the diagnostic typing phage set for enterobacteriaceae Microbiological examination for food hygiene rapid detection of coliform bacteria cereal, fruit and vegetable National Food Safety Standard Microbiological Examination of Food Hygiene - Examination of Bifidobacterium GB examination: Lactic acid bacteria GB/T Escherichia coli O157: H7/NM Page 4 of 17

5 GB/T Staphylococcus aureus GB GB/T GB National Food Safety Standard Microbiological Examination of Food Hygiene - Enumeration of Escherichia Coli Microbiological examination of food hygiene. Enumeration of faecal coliforms examination: Enterobacter sakazakii Page 5 of 17

6 Table of Contents Foreword Scope Terms and Definitions Devices and Materials Culture Medium and Reagents Examination Procedure Operational Procedure Examination Procedure Operational Procedure Annex A Annex B Page 6 of 17

7 Foreword This Standard replaces GB/T Microbiological Examination of Food Hygiene Enumeration of Coliforms. The main changes in this Standard over GB/T are as follows: - Modify standard name of both English and Chinese; - Modify the selection range of plate colony count of Method 2: Coliform Plate Count Method into 15 CFU ~ 150 CFU ; - Delete Method 3: Coliforms Pertifilm TM Test Strip Method. Annex A and Annex B of this Standard are normative. The historical editions replaced by this Standard are as follows: - GB , GB , GB , and GB Page 7 of 17

8 examination: Enumeration of Coliforms 1 Scope This Standard specifies the methods of enumeration of coliforms in food. This Standard is applicable to the enumeration of coliforms in food. 2 Terms and Definitions 2.1 Coliforms Aerobic and facultative anaerobic gram-negative asporous bacilli that can ferment lactose and are acid-producing and aerogenic, under certain culture conditions. 2.2 Most probable number (MPN) An indirect enumeration method based on Poisson distribution. 3 Devices and Materials In addition to conventional sterilization and culture devices in the microbiology laboratory, other devices and materials are as follows: 3.1 Thermostat incubator: 36 ºC ± 1 ºC. 3.2 Refrigerator: 2 ºC ~ 5 ºC. 3.3 Thermostat water bath: 46 ºC ± 1 ºC. 3.4 Balance: sensibility 0.1 g. 3.5 Homogenizer. 3.6 Oscillator. 3.7 Sterile sucking tubes: 1 ml (accurate to 0.01 ml), 10 ml (accurate to 0.1 ml) or micropipette with a sucker. 3.8 Sterile conical flask: 500 ml. 3.9 Sterile petri dish: diameter 90 mm ph meter or ph cuvette tube or precision ph test paper Colony counter. Page 8 of 17

9 8.3 Selection of plate colony count Select the plates with colony counts of 15 CFU 150 CFU and enumerate typical and suspicious coliform colonies on the plates respectively. Typical colonies are claret, around which is zone of precipitated red bile salt. The colonies have a diameter of 0.5 mm or above. 8.4 Confirmation test Pick up 10 typical and suspicious colonies of different types from the plates, then inoculate into BGLB broth tubes respectively, culture at 36 ºC ± 1 ºC for 24 h 48 h and observe the aerogenesis. The BGLB broth tubes with aerogenesis can be reported as coliform positive. 8.5 Reporting of plate enumeration of coliforms The number of coliform groups in each gram (ml) sample is obtained by multiplying the ratio of test tubes which are confirmed to be coliform positive BY the plate colony count in 8.3, and further multiplied by the dilution multiple. For example, 1 ml 10-4 sample diluent has 100 typical and suspicious colonies on the VRBA plate, ten of them are selected to inoculate the BGLB broth tube, six tubes are confirmed to be positive, then the coliform group count of the sample is 100 6/ /g(ml) = CFU/g (ml). Page 13 of 17

10 Annex A (Normative) Culture Medium and Reagents A.1 Lauryl sulfate tryptose (LST) broth A.1.1 Ingredients Tryptone or tryticase Sodium chloride Lactose Pdipotassium hydrogen phosphate (K 2 HPO 4 ) Potassium dihydrogen phosphate (KH 2 PO 4 ) Sodium lauryl sulfate Distilled water 20.0 g 5.0 g 5.0 g 2.75 g 2.75 g 0.1 g ml ph 6.8 ± 0.2 A.1.2 Method of preparation Dissolve the ingredients into the distilled water, adjust ph value, pour the solution into test tubes with an inverted vial, 10 ml for each tube, and perform autoclaving at 121 ºC for 15 min. A.2 Brilliant green lactose bile (GGLB) broth A.2.1 Ingredients Peptone Lactose Oxgall or oxbile powder solution 10.0 g 10.0 g 200 ml 0.1% Brilliant green water solution 13.3 ml Distilled water 800 ml ph 7.2 ± 0.1 A.2.2 Method of preparation Page 14 of 17

11 Annex B (Normative) Search-table to Most Probable Numbers (MPN) of Coliforms B.1 Search-table to Most Probable Numbers (MPN) of coliforms See Table B.1 for most probable numbers (MPN) of coliforms in 1 g (ml) of sample. Table B.1 Search-table to Most Probable Numbers (MPN) of Coliforms Number of positive tubes MPN Lower limit 95% confidence level Upper limit Number of positive tubes MPN Lower limit 95% confidence level < Upper limit > Note 1: There are three dilution rates in this table [0.1 g(ml), 0.01 g(ml) and g(ml)] and each dilution rate is inoculated with three tubes. Note 2: If the amounts of samples in the table are changed into 1 g(ml), 0.1 g(ml) and 0.01 g(ml), figures in the table shall be decreased by 10 times accordingly; if the amounts are changed into 0.01 g(ml), g(ml) and g(ml), figures in the table shall be increased by 10 times accordingly, the rest uses similar method. Page 17 of 17