TITLE: THE DETECTION OF RESIDUES OF ANTI-BACTERIAL SUBSTANCES IN ANIMAL TISSUES (SIX PLATE METHOD) SOP. permitted.

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1 TITLE: THE DETECTION OF RESIDUES OF ANTI-BACTERIAL SUBSTANCES IN ANIMAL TISSUES (SIX PLATE METHOD) SOP No photocopying of or unauthorised hand-written amendments to this document are permitted. Author (Signature) (Printed) DATE Approved(Signature) (Printed) QAU (Signature) (Printed) Implementation date Copy No. (optional) Review Date: (1) (2) L M Signature (1) (2) Review Date: (3) (4)

2 L M Signature (3) (4) 1.0 SAFETY 1.1 All procedures must be carried out in accordance with the VSD Safety Code and the Residue Testing Sections Code of Practice on Safety. 1.2 All chemicals should be used under the conditions stated in the COSHH Assessment. 1.3 Personal safety equipment and clothing should be worn at all times. 1.4 When working with micro-organisms use aseptic techniques. 1.5 Antimicrobial agents:- Care should be taken to avoid aerosols and skin contact. Page! 2 of! 15

3 2.0 INTRODUCTION The test is carried out as an agar diffusion test. Tissue, fish, eggs and QA samples are applied to six plates of agar media inoculated with Bacillus cereus spores (at ph 6.0) Bacillus subtilis spores (at ph 6.0, 7.2 and 8.0), Escherichia coli (at ph 8.0) and Micrococcus luteus (at ph 8.0). Trimethoprim is incorporated into the ph 7.2 medium to enhance the sensitivity towards sulphonamide residues. Diffusion of an antibacterial substance is shown by the formation of zones of inhibition. 3.0 EQUIPMENT 3.1 Incubator set at 36 C (+ 2 C). 3.2 Incubator set at 30 C (+ 2 C). 3.3 Refrigerator. 3.4 Freezer set at -20 C (+ 3 C). 3.5 Water bath set at +55 C (+ 2 C) 3.6 Autoclave portable. 3.7 ph meter. 3.8 Analytical balance ( g). 3.9 Bench press (modified to take cutters) Levelling platform Reading Lamp. Page! 3 of! 15

4 3.12 Spectrophotometer Class II safety cabinet 4.0 MATERIALS 4.1 Chemicals All chemicals are ANALAR Grade unless otherwise stated Methylated Spirits (GPR) Ethanol (HPLC Grade) Trimethoprim (Sigma) Tryptone (Oxoid). 5. Sodium chloride Hydrochloric acid (0.1M) Sodium hydroxide (0.1M). 4.2 Apparatus 1. Stainless steel cutters (100 mm x 8mm) Bioassay dishes (size 243 mm x 243 mm x 18 mm) Finnpipettes ( µl, µl) Sterile Finnpipette tips ( µl, µl) Cellulose membrane 325P (Wolff Walsnode). 6. Paper plates, 8½" diameter Metal pushers ml pyrex measuring cylinder. 9. Sterile glass universal bottles. Page! 4 of! 15

5 ml pyrex volumetric flasks. 11. Bijou bottles Metric ruler Glass balls (size: 4.5 mm to 5.5 mm) BDH Media bottles (DIFCO) Sterile Pasteur pipettes Cork Borer No Sterile plastic universal bottles. 4.3 Reagents Distilled water Sterile distilled water Peptone Salt Solution. Dissolve 1 g ( g) tryptone (4.1.4) with 8.5 g ( g) sodium chloride in 1000 ml distilled water. Mix well using a magnetic stirrer. Check ph is 7.2 (+ 0.1) at 25 C on ph meter. If necessary, adjust using 0.1M hydrochloric acid solution (4.1.6) or 0.1 M sodium hydroxide solution (4.1.7). Dispense the solution in 20 ml amounts into glass universal bottles and sterilise. Store at room temperature for up to 1 year Sterile Beads and Peptone Salt Solution. Glass beads (4.2.13) are pre-soaked in 0.1M HCl (4.1.6) and rinsed with distilled water until ph7 is reached. Dispense approximately of the washed beads into glass universals with 10 ml peptone salt solution (4.3.3) and sterilise. Store at room temperature for up to 1 year. Page! 5 of! 15

6 4.3.6 Trimethoprim The specific activity (potency/mg of preparation) varies from batch to batch. Thus to achieve a certain potency, the amount of standard weighed will vary. Weigh approximately 10 mg (+ 0.5 mg) of the standard substance (4.1.3) corrected for potency. Dissolve in 10 ml of ethanol and make up to 100 ml with sterile distilled water to obtain a solution of 100 µg/ml. Add 10 ml of this solution to a volumetric flask and make up to 100 ml with sterile distilled water to obtain a solution of 10 µg/ml. Dispense 2 ml into sterile bijou bottles and store at -20 C. This solution is stable for 1 month. 4.4 Organisms Bacillus subtilis BGA Micrococcus luteus ATCC Bacillus subtilis BGA freeze dried culture (NCIMB 8054) 4. Bacillus cereus ATCC Escherichia coli: ATCC Media Test agar ph 6.0 (Merck) Test agar ph 7.2 (Merck) Test agar ph 8.0 (Merck) Nutrient Agar Slopes. (Prepared by media central services, refer to relevant SOP). Page! 6 of! 15

7 4.5.5 Nutrient Agar Plates. (Prepared by media central services, refer to relevant SOP). 4.6 CONTROLS Penicillin G discs (Mast Diagnostics 0.01 units/disc) Streptomycin discs (Mast Diagnostics 0.5 µg/disc) Sulphadimidine discs (Mast Diagnostics 0.5 µg/disc). 4. Erythromycin discs (Mast Diagnostics µg/disc). 5. Oxytetracycline discs (Mast Diagnostics 0.5 µg/disc). 6. Ciprofloxacin discs (Mast Diagnostics µg/disc). 5.0 METHOD PREPARATION 5.1 Preparation of the Bacillus subtilis spore suspension Bacillus subtilis spores are stored in 1ml aliquots at -70ºC. When required dilute the 1 ml aliquots with 10 ml of peptone salt solution to obtain a light transmission of 75% (+ 5%) at 680 nm in a 10 mm cell using peptone salt solution as a reference Mix gently end over end by hand and store at +4 C. Use within 1 month Determine the volume of inoculum required on the ph 6, ph 7.2 and ph 8 test plates. 5.2 Preparation of Micrococcus luteus suspension Take a freshly prepared culture of M. luteus (4.4.2) on nutrient agar slopes Wash the slopes with sterile beads and 3 ml of peptone salt solution (4.3.5) by gently allowing the beads to move along the slope taking the culture into suspension. Page! 7 of! 15

8 3. Using a sterile Pasteur pipette remove the peptone salt solution containing M. luteus and place in a sterile plastic universal bottle Make up to 10 ml with peptone salt solution and dilute with peptone salt solution to obtain a light transmission of 45% (+ 5%) at 680 nm in a 10 mm cell using peptone salt solution as a reference. 5. Store at +4 C. Use within 1 month Determine the volume of inoculum required on ph8 test plates. 3. Preparation of the Bacillus cereus spore suspension 1. Bacillus cereus spores are stored in 1ml aliquots at -70ºC. 2. When required dilute the 1ml aliquots with 10 ml of peptone salt solution to obtain a light transmission of 75% (+ 5%) at 680 nm in a 10mm cell using peptone salt solution as a reference. 3. Mix gently end over end by hand and store at +4ºC. Use within 1 month. 4. Determine the volume of inoculum required on the ph6 test plate. 2. Preparation of Escherichia coli suspension 2.1. Take a freshly prepared culture of E. coli on nutrient agar slopes Wash the slopes with 10 glass beads and 2ml peptone-salt solution (4.3.5) by gently allowing the beads to move along the slope taking the culture into suspension Using a sterile pasteur pipette remove the peptone-salt solution containing E. coli and place in a sterile universal bottle Dilute with peptone-salt solution to give an optical density of at 620 nm in a 10 mm cell using peptone-salt solution as a reference Store at + 4ºC. Use within 1 month. Page! 8 of! 15

9 2.6. Determine the volume of inoculum required on ph 8 test plates. 5.5 Preparation of Test Media Test Agar Amount Distilled H 2 O ph g 8L ph g 8L ph g 8L 5.6 Preparation of Test Plates Melt the sterile bottles of media in a portable autoclave. 2. Place in a waterbath at 55 C and leave for at least 30 min until they reach the temperature of the waterbath Add the appropriate innoculum of micro-organism suspension to the media. (5.1.1) (5.2.6) (5.3.1) (5.4.6). Add 200 µl of Trimethoprim (4.3.6) to each 40 ml bottle of ph 7.2 media Pour media into bioassay dishes which have been placed on a levelling platform as follows: Test Plate ph B. subtilis ph B. subtilis + Trimethoprim ph B. subtilis ph M. luteus ph B. cereus ph E. coli Volume of Media 40ml 40ml 40ml 40ml 40ml 40ml Page! 9 of! 15

10 5.6.5 Label each plate with the plate number, preparation and expiry dates, ph and batch number of the media and the initials of the analyst who prepared the plates Store test plates at 4 C for a maximum of 5 days. The ph8 E. coli can be stored for up to 3 days. 5.7 Preparation of Cellulose Membrane Cut the cellulose membrane into 2.5 cm x 2.5 cm squares and store in a petri dish Place each test plate on a template (Appendix 1) and place a cellulose membrane square on every row. Except when testing eggs or milk in wells. 6.0 METHOD 6.1 Testing of Frozen Tissue Samples 1. Remove the tissue samples from the freezer and allow to sit at room temperature for up to 20 min. 2. Cut a cylindrical core from each tissue using the bench press and a stainless steel cutter Push the frozen core from the cutter onto a paper plate using a sterilised metal pusher Cut six to twelve slices of 2 mm thickness using a sterile scalpel blade Discard both end slices and any slices which contain fat For all samples (except for Phase I and Suspect Bovine Scheme (SBS) samples see below), place two slices from each tissue on each of six plates using forceps. One slice is placed in the centre of the cellulose membrane Page! 10 of 15!

11 square and the other slice on the centre of the cellulose membrane square in the row directly below. For Phase I and SBS testing, place one slice from each tissue on each of six plates using forceps in the centre of the cellulose membrane square Sterilise the metal pusher and scalpel blade between samples by immersion in a 100 ml measuring cylinder filled with methylated spirits and wipe off the excess with a paper serviette. 8. After each day's testing immerse the bench press holder in methylated spirits and leave overnight. 6.2 Testing of Fresh Tissue Samples Proceed from Sterilise the metal pusher and scalpel blade between samples by immersion in a 100 ml measuring cylinder filled with methylated spirits and wipe off the excess with a paper serviette. 6.3 Testing of Fish Ensure all skin is removed from the fish and freeze tissue Proceed from Testing of Eggs Place each test plate on a template (Appendix 1). Cut a well using a number 6 cork borer. Cut enough wells to test each egg sample in duplicate. 2. Separate each egg yolk and white. Discard the white. Page! 11 of! 15

12 3. Using a fresh pipette tip for every sample fill 2 wells with yolk on each of the six plates for each sample. 6.5 Antimicrobial Control Disks An antimicrobial control disc is placed in the bottom right corner of each plate. TEST PLATE ANTIMICROBIAL CONTROL MINIMUM DISK ZONE SIZE 1. ph B. subtilis Penicillin G 18mm 2. ph B. subtilis Sulphadimidine 18mm + Trimethoprim 3. ph B. subtilis Streptomycin 22mm 4. ph M. luteus Erythromycin 23mm 5. ph B. cereus Oxytetracycline 14 mm 6. ph E. coli Ciprofloxacin 18 mm 6.6 Incubation of Test Plates Plates are stored, if necessary, at +4 C before placing in incubator The test plates are incubated at 30 C for approximately 18 h. 6.7 Reading of Test Plates Measure the zones of inhibition given by the tissue slices and control discs (to the nearest mm) using a ruler Read plates against a black background with a light from underneath Fill the results in on the results sheet (RU58) (Refer to form master file). Page! 12 of 15!

13 6.8 Sensitivity The sensitivity of the test plates is monitored by measuring the zones of inhibition given by the antimicrobial control discs which must equal or exceed the minimum zone size given in the table (6.5). 7.0 INTERPRETATION OF RESULTS 7.1 A positive result is indicated by the complete inhibition of growth around both meat slices (or meat slice for Phase I and SBS samples) from a sample on one or more test plates, in a zone of 12 mm radius or greater. 1. A negative result is indicated by no inhibition of growth around the tissue slice on the cellulose membrane. 7.3 The six plate test is repeated in cases where the result is inconclusive. If again the result is not clearly interpretable, the sample is declared negative. 7.4 For those samples which appear to be positive for the following groups of antibiotics:- (a) Tetracyclines - largest zone of inhibition on ph 6.0 plate B. cereus and B. subtilis (b) Sulphonamides - largest zone of inhibition on ph 7.2. plate (c) Penicillins similar sized zones of inhibition on ph 6, 7.2, ph 8 B. subtilis and ph 8 ML (d) Tilmicosin largest zone of inhibition on ph 8ML plate. Page! 13 of 15!

14 Approximately half of the tissue sample is sent to the CCU laboratory for confirmation and quantification of the inhibitory substances. 5. For all other positives not covered in sections 7.4 or for any positive result for which it is unsure as to the nature of the inhibitory substance present samples may be assayed further by High Voltage Electrophoresis. No action is taken if no confirmatory assay is available or the Study Director feels no further analysis is required. 8.0 REFERENCES 8.1 Bogarts, R and Wolf, F (1980). A standardised method for the detection of residues of anti-bacterial substances in fresh meat. Die Fleischwirtschaft Document UCM 90/01/Rev 1/En (1993). Method of detecting residues of anti-bacterial substances in fresh meat. Four Plate Test. Laboratoire des Medicaments Veterinaires APPENDICES 9.1 Appendix I - Diagram of plate. Page! 14 of 15!

15 Lay-out of Tissue Samples and Dialysis Membrane on SPT X CONTROL Dialysis membrane. Tissue sample. Page! 15 of 15!

3.1 Microbiological assay of antibiotics

3.1 Microbiological assay of antibiotics The potency (activity) of an antibiotic product is expressed as the ratio of the dose that inhibits the growth of a suitable susceptible microorganism to the dose of an International Biological Standard,