Test for Total Microbial Count is provided to determine compliance with the requirements given in individual monograph / specifications.
PRINCIPLE
Total microbial count is the estimation of the number of viable aerobic micro-organisms present in the pharmaceutical articles of all kinds, from raw materials to the finished forms.
BUFFERS AND MEDIA
1. pH 7.2 Phosphate Buffer
Stock Solution
Dissolve 34 g of Monobasic Potassium Phosphate in about 500 mL of water contained in a 1000 mL volumetric flask. Adjust to pH 7.2 ± 0.1 by the addition of 4 % w/v aqueous solution of Sodium Hydroxide (about 175 mL), add water to volume, and mix. Dispense and sterilize. Store under refrigeration.
For use, dilute the Stock Solution with water in the ration of 1 to 800 , and sterilize in an autoclave at 121 OC , 15 lb pressure for about 15 min.
2. Fluid Soyabean Casein Digest Medium
Pancreatic Digest of Casein 17.0 g
Papacy Digest of Soybean Meal 3.0 g
Sodium Chloride 5.0 g
Dibasic Potassium Phosphate 2.5 g
Dextrose (C6H12O6. H2O) 2.5 g
Distilled Water 1000 mL
Final pH after Sterilization 7.3 ± 0.2
Dissolve the solids in the water, warming slightly to effect solution. Cool to room temperature and adjust pH. 7.3 ± 0.2 and Filter, if necessary. Distribute the media into suitable containers and sterilize in an autoclave at 121 OC for about 15min.
3. Fluid Casein Digest-Soy Lecithin-Polysorbate 20 Medium
Pancreatic Digest of Casein 20.0 g
Soy Lecithin 5.0 g
Polysorbate 20 40 mL
Water 960 mL
Dissolve the pancreatic digest of casein and soy lecithin in 960 mL of water, heating in a water batch at 48 - 50 OC for about 30 min. to effect solution. Add 40 mL of Polysorbate 20. Mix, and dispense as desired and sterilize in an autoclave at 121 OC for about 15min..
4. Sabouraud Glucose Agar with Antibiotics
Peptones (meat and Casein) 10.0 g
D- Glucose Monohydrate 40.0 g
Agar 15.0 g
Water 1000 mL
Adjust the pH to 5.4 +2. Sterilize by heating in an autoclave at 121 OC for 15 min. Immediately before use, add 0.10 g of Benzylpenicillin Sodium and 0.10 g of Tetracycline per liter of medium as sterile solutions or, alternatively, add 50 mg of Chloramphenicol per liter of medium.
5. Peptone Water
(Buffered Sodium Chloride - Peptone Solution pH 7.0)
Potassium Dihydrogen Orthophosphate 3.56 g
Disodium Hydrogen Orthophosphate 7.23 g
Sodium Chloride 4.30 g
Peptone(meat and Casein) 1.0 g
Water 1000 mL
0.1 to 1.0 % w/v Polysorbate 20 or Polysorbate 80 may be added. Sterilize by heating in an autoclave at 121 OC for 15 min.
6. Potato Dextrose Agar Medium
Cook 300 g of peeled and diced potatoes in 500 mL of water prepared by distillation, filter through cheesecloth, add water prepared by distillation to make 1000 mL and add the following :
Agar 15 mg
Glucose 20 mg
pH after sterilization 5.6 ± 0.2
Dissolve by heating, and sterilize.
For use, just prior to pouring the plates, adjust the melted and cooled medium to 45 OC with Sterile Tartaric Acid solution (1 in 10) to a pH of 3.5 ± 0.1 Do not reheat the pH 3.5 medium.
All the above media should be incubated for 24 hours at 37 OC before use. Any contaminated media should be discarded.
Instead of preparing media , one can also use dehydrated media of Hi media / Difco and rehydrate the required quantity as per instructions on the bottle label, dispense in required quantities and sterilize.
Preliminary Testing
The methods given herein are invalid unless it is demonstrated that the test specimens to which they are applied to not, of themselves, inhibit the multiplication, under the test conditions, of micro-organisms that may be present. Therefore, prior to doing the tests, inoculate diluted specimens of the substance being examined, with separate viable cultures of Escherichia coli, B. subtilis and Staphylococcus aureus. Add 1 mL of not less than 10 -3 dilution of a 24 hour broth culture of the micro-organism to the first dilution (in buffer solution pH 7.2 , Fluid Soybean-Casein Digest medium, of the test material and following the test procedure. If the organisms fail to grow in the relevant medium the procedure should be modified by
a. increasing the volume of diligent, the quantity of test material remaining the same,
b. incorporating a sufficient quantity of a suitable inactivating agent in the diluents or by,
c. combining the afore-mentioned modifications so as to permit growth in the media.
If inhibitory substances are present in the sample 0.5 % of soy lecithin and 4 % of the Polysorbate 20 may be added to the culture medium.. Alternatively, repeat the test as described in the previous paragraph, using fluid casein digest - soy lecithin - polysorbate 20 medium to demonstrate neutralization of preservatives or other anti-microbial agents in the test material.
PRE - TREATMENT OF THE PREPARATION BEING EXAMINED
Use separate 10 mL or 10 g specimens for testing.
Water - Soluble Products :
Dissolve or dilute 10 g or 10 mL of the preparation being examined, unless otherwise prescribed, in Peptone Water or another suitable medium shown not to have anti-microbial activity under the conditions of the test and adjust the volume to 100 mL with the same medium. If necessary, adjust the pH to about 7.
Non - Fatty Products Insoluble in Water :
Suspend 10 g or 10 mL of the preparation being examined, unless otherwise prescribed, in Peptone Water or another suitable medium shown not to have anti-microbial activity under the conditions of the test and dilute to 100 mL with the same medium. If necessary divide the preparation being examined and homogenize the suspension mechanically.
A suitable surface - active agent such as 0.1 % w/v of Polysorbate 80 may be added to assist the suspension of poorly wettable substances. If necessary, adjust the pH of the suspension to
about 7
Fatty Products :
Homogenize 10 g or 10 mL of the preparation being examined, unless otherwise prescribed with 5 g of Polysorbate 20 or Polysorbate 80. If necessary, heat to not more than 40 OC . Mix carefully while maintaining the temperature in a water bath or in an oven. Add 85 mL of Peptone Water or another suitable medium shown not to have anti-microbial activity n the conditions of the test, heated to not more than 40 OC if necessary. Maintain this temperature for the shortest time necessary for formation of an emulsion and in any case for not more than 30 min. If necessary, adjust the pH of the emulsion to about 7.
For a Fluid Specimen in Aerosol Form :
Chill the container in an Alcohol-dry ice mixture for approximately 1 h, cut open the container, allow it to reach room temperature, permit the propellant to escape, or warm to drive off the propellant if feasible and transfer the quantity of test material required for the procedures specified in one of the two preceding paragraphs, as appropriate. Where 10 g or 10 mL of the specimen, whichever is applicable, cannot be obtained from 10 containers in aerosol form, transfer the entire contents from 10 chilled containers to the culture medium, permit the propellant to escape, and proceed with the test on the residues.
Effectiveness of Culture Media and Validity of the Counting Methods :
When necessary, operate as follows. Grow the following test strains separately in tubes containing casein soybean digest broth at 30 - 35 OC for 18 - 24 hours or, for Candida albicans, at 20 -25 OC for 48 hours.
Staphylococcus aureus such as NCIMB 8625 (ATCC 6538, CIP 530156) or NCIMB 9518 (ATCC 6538, CIP 4038)
Bacillus Subtilis, such as NCIMB 8054 ( ATCC 6633, CIP 52.62)
Candida albicans, such as ATCC 2091 (CIP 1180.79) or ATCC 10231 (NCPF 3179, CIP 48.72)
Dilute portions of each of the cultures using buffered sodium chloride - peptone solution pH 7.0 to make test suspensions containing about 100 viable micro-organisms per milliliter. Use the suspension of each of the micro-organisms separately as a control of the counting methods in the presence and absence of the preparation being examined if necessary.
When testing the method, a count for any of the test organisms differing by not more than a factor of 10 from the calculated value for the inoculum should be obtained. To test the sterility of the medium and of the diligent and the aseptic performance of the test, carry out the total viable aerobic count method using sterile buffered sodium chloride - peptone solution pH 7.0 as the test preparation. There should be no growth of micro-organisms.
PROCEDURE
As per IP
1. Dissolve or suspend 10 g of the substance being examined in sufficient buffer solution, pH 7.2, Fluid Soybean - Casein Digest Medium, or Fluid Casein Digest-Soy lecithin - Polysorbate 20 medium to produce 100 mL.
2. Perform the test for the absence of inhibitory (anti-microbial) properties as described under Preliminary Testing before the determination of Total Microbial Count.
3. Add the substance being examined, to the medium not more than 1 hour after preparing the appropriate dilution’s for inoculation.
A. Plate Method
This method is applicable for substances that are sufficiently soluble or translucent.
1. Dilute further, if necessary, the sample liquid prepared as described above, so that 1 mL will be expected to yield between 30 to 300 colonies.
2. Pipette 1 mL of the final dilution into each of two sterile petri dishes.
3. Immediately add to each dish 15 to 20 mL of Soybean-Casein digest agar medium that has previously been melted and cooled to about 45 OC.
4. Cover the petridishes, mix the sample with the agar by tilting or rotating the dishes, and allow the contents to solidify to room temperature.
5. Invert the petri dishes, and incubate for 48 to 72 hours at 37 OC.
6. After incubation examine the plates of growth, count the number of colonies, and express the average for the two plates in terms of number of micro-organisms per g of the substance.
7. If no colonies are recovered from the dishes representing the initial 1 : 10 dilution of the substance, express the results as “less than 10 micro-organisms per g of substance”.
B. Multiple - Tube Method
This method is applicable for substances that are insoluble or not translucent.
1. Into each of the fourteen test tubes of similar size place 9 mL of sterile Fluid Soyabean casein digest medium.
2. Arrange 12 of the tubes in four sets of three tubes each. Put aside one set of three tubes to serve as the controls.
3. Into each of three tubes of one set [“100” ] and into fourth tube (A) pipette 1 mL of the Solution of suspension of the specimen, and mix.
4. From tube A pipette 1 mL of its contents into the one remaining tube (B) not included in a set, and mix.
5. These two tubes contain 100 mg (or 100 µl) and 10 mg (10 µl) of the specimen respectively.
6. Into each of the second set [“10”] of three tubes pipette 1 mL from tube A and into each tube of the third set [“1”] pipette 1 mL from tube B.
7. Discard the unused contents of tubes A and B.
8. Close well, and incubate all of the tubes.
9. Following the incubation period, examine the tubes for growth; the three control tubes remain clean and the observations in the tubes containing the specimen, when interpreted by reference to Table I. indicate the most probable number of micro-organisms per g or per mL of specimen.
As per BP
Determine the total viable aerobic count of the preparations being examined by the membrane filtration method, the plate count method or the serial dilution method as prescribed. Suitable degrees of dilution should be used so that the number of colony forming units is within the limits suggested for the method to be used.
A. Membrane Filtration
Use membrane filters having a normal pore size not greater than 0.45 µm and 50 nm in diameter the effectiveness of which in retaining bacteria has been established. For example, Cellulose nitrate filters are used for aqueous, oily and weakly alcoholic solutions and Cellulose acetate filters for strongly alcoholic solutions.
1. The filtration apparatus and membrane are sterilized by appropriate means and are designed so that the solution being examined can be introduced and filtered under aseptic conditions and so as to permit the removal of the membrane for transfer to the culture medium.
2. Transfer 10 mL or a quantity to each of two membrane filters and filter immediately.
3. If necessary, dilute the pretreated preparation so that a colony count of 10 to 100 may be expected.
4. Wash each membrane by filtering through it three or more successive quantities , each of approximately 100 mL, of a suitable liquid such as buffered Sodium Chloride - peptone pH 7.0. For fatty substances, this liquid may contain a suitable surface active agent such as polysorbate 20 or polysorbate 80. Transfer one of the membrane filters, intended primarily for the enumerate of bacteria, to the surface of the plate of casein soybean digest agar and the other, intended primarily for the surface of a plate of sabouraud glucose agar with antibiotics.
5. Incubate the plates for 5 days, unless a more reliable count is obtained in a shorter time, at 30 - 35OC in the test intended to detect bacteria and at 20 - 25 OC in the test intended to detect fungi.
6. Count the number of colonies that are formed. Calculate the number of micro-organisms per gram or per milliliter of the preparation being examined, if necessary counting bacteria and fungi separately.
B. Plate Count
i. For Bacteria
1. Using petri dishes 9 to 10 cm in diameter, add to each dish a mixture of 1 mL of the pretreated preparation and about 15 mL of liquefied casein soyabean digest agar at not more than 45 OC .
2. Alternatively, spread the pretreated preparation on the surface of the solidified medium in a petri dish of the same diameter.
3. If necessary, dilute the pre-treated preparation as described above so that a colony count of not more than 300 may be expected.
4. Prepare at least two such petri dishes using the same dilution and incubate at 30 - 35OC for unless a more reliable count is obtained in a shorter time.
5. Count the number of colonies that are formed.
6. Calculate the results using plates with the greatest number of colonies but taking 300 colonies per plate as the maximum consistent with good evaluation.
ii. For Fungi
1. Using petri dishes 9 - 10 cm in diameter, add to each dish a mixture of 1 mL of the pre-treated preparation and about 15 mL of liquefied Sabouraud glucose agar with antibiotics at not more than 45 OC.
2. Alternatively, spread the pretreated preparation on the surface of the solidified medium in a petri dish of the same diameter. If necessary, diluted the pretreated preparation as described above so that a colony count of not more than 100 may be expected.
3. Prepare atleast two such plates using the same dilution and incubate at 20 - 25 OC for 5 days, unless a more reliable count is obtained in a shorter time.
4. Count the colonies that are formed. Calculate the results using plates with not more than 100 colonies.
Serial Dilution
1. Prepare a series of 12 tubes each containing 9 - 10 mL of caseing soyabean digest broth.
2. To each of the first three tubes add 1 mL of the preparation diluted, dissolved or homogenized in the proportion 1 in 10 , as described above.
3. To the next three tubes add 1 mL of a 2 in 100 dilution of the preparation and to the next three tubes add 1 mL of a 1 in 100 dilution of the preparation.
4. To the last three tubes add 1 mL of the diligent.
5. Incubate the tubes at 30 - 35 OC for at least 5 days.
6. The last three tubes should show no microbial growth.
7. If the reading of the results is difficult or uncertain owing to the nature of the preparation being examined, sub-culture on a liquid or solid medium and read the results after a further period of incubation.
8. Determine the most probable number of micro-organisms per gram or per milliliter of the preparation being examined from Table I.
As per USP
1. For specimens that are sufficiently soluble or translucent to permit use of the plate Method, otherwise, use Multiple-tube Method.
2. With either method, first dissolve or suspend 10 g of the specimen if it is a solid, or 10 mL , accurately measured if the specimen is a liquid, in pH 7.2 Phosphate Buffer, Fluid Soyabean-Casein Digest Medium, or Fluid Casein Digest-soy Lecithin - Polysorbate 20 Medium to make 100 mL
3. For viscous specimens that cannot be pipetted at this initial 1:10 dilution, dilute the specimen until a suspension is obtained i.e., 1:50 or 1: 100 etc., that can be pipetted.
4. Perform the test for absence of inhibitory (anti-microbial) properties as described under Preparatory Testing before the determination of Total Aerobic Microbial Count.
5. Add the specimen to the medium not more than 1 h after preparing the appropriate dilution’s for inoculation.
A. Plate Method
1. Dilute further, if necessary, the fluid so that 1mL will be expected to yield between 30 and 300 colonies.
2. Pipette 1 mL of the final dilution onto each of two sterile petridishes.
3. Promptly add to each dish 15 - 20 mL of Soyabean Casein Digest Agar Medium when testing for bacteria and add 15 - 20 mL Sabouraud Dextrose Agar medium or Potato Dextrose Agar medium for molds and yeasts,. that previously has been melted and cooled to approx. 45 OC.
4. Cover the petridishes, mix the sample with the agar by tilting or rotating the dishes, and allow the contents to solidify at room temperature.
5. Invert the petridishes, and incubate for 48 - 72 hours at 37 OC for bacteria and incubate for 5 - 7 days at 20 - 25 OC for molds and yeasts.
6. Following incubation, examine the plates for growth, count the number of colonies, and express the average for the two plates in terms of the number of micro-organisms per g or per mL of specimen.
7. If no microbial colonies are recovered from the dishes representing the initial 1 : 10 dilution of the specimen, express the results as “less than 10 micro-organisms per g or per mL of specimen.”
B. Multiple Tube Method
1. Place 9 mL of sterile Fluid Soybean casein digest medium into each of fourteen test tubes of similar size.
2. Arrange twelve of the tubes in four sets of the three tubes each.
3. Put aside one set of three tubes to serve as the controls.
4. Into each of three tubes of one set [“100”] and into a fourth tube (A) pipette 1 mL of the solution or suspension of the specimen, and mix.
5. From tube a , pipette 1 mL of its contents into the one remaining tube (B) not included in a set, and mix. These two tubes contain 100 mg (100 µl) and 10 mg (10 µl) of the specimen, respectively.
6. Into each of the second set [“10”] of three tubes pipette 1 mL from the tube A, and into each tube of the third set [“1”] pipette 1 mL from tube B.
7. Discard the unused contents of tubes A and B.
8. Close well, and incubate all of the tubes. Following the incubation period, examine the tubes for growth; the three control tubes remain clear and the observation in the tubes containing the specimen, when interpreted by reference to Table I, indicate the most probable number of micro-organisms per g r per mL of specime
Most Probable Count by Multiple - Tube Method
TABLE - I


Calculations
Take the average count of each dilution and multiply it by the dilution factor. Calculate the average form the readings obtained. This gives the count per gram or per mL of the sample/
Interpretation of Results :
If a limit is prescribed, it is to be interpreted as follows :
10 2 micro-organisms, MAXIMUM LIMIT OF ACCEPTANCE: 5 x 10 2
10 3 micro-organisms, MAXIMUM LIMIT OF ACCEPTANCE : 5 x 10 3
NOTE: Use the method as per the pharmacopoeial status (grade) of the material. In case of In- house specifications, follow the method as per the IP or as specified