62 MICROBIOLOGICAL EXAMINATION OF NONSTERILE PRODUCTS: TESTS FOR SPECIFIED MICROORGANISMS

INTRODUCTION
The tests described hereafter will allow determination of the absence of, or limited occurrence of, specified microorganisms that may be detected under the conditions described.
The tests are designed primarily to determine whether a substance or preparation complies with an established specification for microbiological quality. When used for such purposes, follow the instructions given below, including the number of samples to be taken, and interpret the results as stated below.
Alternative microbiological procedures, including automated methods, may be used, provided that their equivalence to the Pharmacopeial method has been demonstrated.

GENERAL PROCEDURES
The preparation of samples is carried out as described in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61.
If the product to be examined has antimicrobial activity, this is insofar as possible removed or neutralized as described in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61.
If surface-active substances are used for sample preparation, their absence of toxicity for microorganisms and their compatibility with any inactivators used must be demonstrated as described in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61.

GROWTH-PROMOTING AND INHIBITORY PROPERTIES OF THE MEDIA, SUITABILITY OF THE TEST AND NEGATIVE CONTROLS
The ability of the test to detect microorganisms in the presence of the product to be tested must be established. Suitability must be confirmed if a change in testing performance or a change in the product that may affect the outcome of the test is introduced.
Preparation of Test Strains
Use standardized stable suspensions of test strains as stated below. Seed-lot culture maintenance techniques (seed-lot systems) are used so that the viable microorganisms used for inoculation are not more than five passages removed from the original master seed-lot.
aerobic microorganisms
Grow each of the bacterial test strains separately in containers containing Soybean–Casein Digest Broth or on Soybean–Casein Digest Agar at 30 to 35 for 18 to 24 hours. Grow the test strain for Candida albicans separately on Sabouraud Dextrose Agar or in Sabouraud Dextrose Broth at 20 to 25 for 2 to 3 days.
Staphylococcus aureus such as ATCC 6538, NCIMB 9518, CIP 4.83, or NBRC 13276
Pseudomonas aeruginosa such as ATCC 9027, NCIMB 8626, CIP 82.118, or NBRC 13275
Escherichia coli such as ATCC 8739, NCIMB 8545, CIP 53.126, or NBRC 3972
Salmonella enterica subsp. enterica serovar Typhimurium or, as an alternative, such as ATCC 14028
Salmonella enterica subsp. enterica serovar Abony such as NBRC 100797, NCTC 6017, or CIP 80.39
Candida albicans such as ATCC 10231, NCPF 3179, IP 48.72, or NBRC 1594
Use Buffered Sodium Chloride–Peptone Solution pH 7.0 or Phosphate Buffer Solution pH 7.2 to make test suspensions. Use the suspensions within 2 hours or within 24 hours if stored at 2 to 8.
clostridia
Use Clostridium sporogenes such as ATCC 11437 (NBRC 14293, NCIMB 12343, CIP 100651) or ATCC 19404 (NCTC 532 or CIP 79.3). Grow the clostridial test strain under anaerobic conditions in Reinforced Medium for Clostridia at 30 to 35 for 24 to 48 hours. As an alternative to preparing and then diluting down a fresh suspension of vegetative cells of Cl. sporogenes, a stable spore suspension is used for test inoculation. The stable spore suspension may be maintained at 2 to 8 for a validated period.
Negative Control
To verify testing conditions, a negative control is performed using the chosen diluent in place of the test preparation. There must be no growth of microorganisms. A negative control is also performed when testing the products as described under Testing of Products. A failed negative control requires an investigation.
Growth Promotion and Inhibitory Properties of the Media
Test each batch of ready-prepared medium and each batch of medium prepared either from dehydrated medium or from ingredients. Verify suitable properties of relevant media as described in Table 1.
Table 1. Growth Promoting, Inhibitory, and Indicative Properties of Media
Test/Medium Property Test Strains
Test for bile-tolerant Gram-negative bacteria
Enterobacteria Enrichment Broth Mossel Growth promoting E. coli
    P. aeruginosa
  Inhibitory S. aureus
Violet Red Bile Glucose Agar Growth promoting + Indicative E. coli
    P. aeruginosa
Test for Escherichia coli
MacConkey Broth Growth promoting E. coli
  Inhibitory S. aureus
MacConkey Agar Growth promoting + Indicative E. coli
Test for Salmonella
Rappaport Vassiliadis Salmonella Enrichment Broth Growth promoting Salmonella enterica subsp. enterica serovar Typhimurium or
    Salmonella enterica subsp. enterica serovar Abony
  Inhibitory S. aureus
Xylose Lysine Deoxycholate Agar Growth promoting + Indicative Salmonella enterica subsp. enterica serovar Typhimurium or
    Salmonella enterica subsp. enterica serovar Abony
Test for Pseudomonas aeruginosa
Cetrimide Agar Growth promoting P. aeruginosa
  Inhibitory E. coli
Test for Staphylococcus aureus
Mannitol Salt Agar Growth promoting + Indicative S. aureus
  Inhibitory E. coli
Test for Clostridia
Reinforced Medium for Clostridia Growth promoting Cl. sporogenes
Columbia Agar Growth promoting Cl. sporogenes
Test for Candida albicans
Sabouraud Dextrose Broth Growth promoting C. albicans
Sabouraud Dextrose Agar Growth promoting + Indicative C. albicans
Test for Growth-Promoting Properties, Liquid Media— Inoculate a portion of the appropriate medium with a small number (not more than 100 cfu) of the appropriate microorganism. Incubate at the specified temperature for not more than the shortest period of time specified in the test. Clearly visible growth of the microorganism comparable to that previously obtained with a previously tested and approved batch of medium occurs.
Test for Growth-Promoting Properties, Solid Media— Perform Surface-Spread Method (see Plate-Count Methods under Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61), inoculating each plate with a small number (not more than 100 cfu) of the appropriate microorganism. Incubate at the specified temperature for not more than the shortest period of time specified in the test. Growth of the microorganism comparable to that previously obtained with a previously tested and approved batch of medium occurs.
Test for Inhibitory Properties, Liquid or Solid Media— Inoculate the appropriate medium with at least 100 cfu of the appropriate microorganism. Incubate at the specified temperature for not less than the longest period of time specified in the test. No growth of the test microorganism occurs.
Test for Indicative Properties— Perform Surface-Spread Method (see Plate-Count Methods under Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61), inoculating each plate with a small number (not more than 100 cfu) of the appropriate microorganism. Incubate at the specified temperature for a period of time within the range specified in the test. Colonies are comparable in appearance and indication reactions to those previously obtained with a previously tested and approved batch of medium.
Suitability of the Test Method
For each new product to be tested perform sample preparation as described in the relevant paragraph under Testing of Products. At the time of mixing, add each test strain in the prescribed growth medium. Inoculate the test strains individually. Use a number of microorganisms equivalent to not more than 100 cfu in the inoculated test preparation.
Perform the test as described in the relevant paragraph under Testing of Products using the shortest incubation period prescribed.
The specified microorganisms must be detected with the indication reactions as described under Testing of Products.
Any antimicrobial activity of the product necessitates a modification of the test procedure (see Neutralization/Removal of Antimicrobial Activity under Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61).
For a given product, if the antimicrobial activity with respect to a microorganism for which testing is prescribed cannot be neutralized, then it is to be assumed that the inhibited microorganism will not be present in the product.

TESTING OF PRODUCTS
Bile-Tolerant Gram-Negative Bacteria
Sample Preparation and Pre-Incubation— Prepare a sample using a 1 in 10 dilution of not less than 1 g of the product to be examined as described in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61, but using Soybean–Casein Digest Broth as the chosen diluent, mix, and incubate at 20 to 25 for a time sufficient to resuscitate the bacteria but not sufficient to encourage multiplication of the organisms (usually 2 hours but not more than 5 hours).
Test for Absence— Unless otherwise prescribed, use the volume corresponding to 1 g of the product, as prepared in Sample Preparation and Pre-Incubation, to inoculate Enterobacteria Enrichment Broth Mossel. Incubate at 30 to 35 for 24 to 48 hours. Subculture on plates of Violet Red Bile Glucose Agar. Incubate at 30 to 35 for 18 to 24 hours.
The product complies with the test if there is no growth of colonies.
Quantitative Test—
Selection and Subculture— Inoculate suitable quantities of Enterobacteria Enrichment Broth Mossel with the preparation as directed under Sample Preparation and Pre-Incubation and/or dilutions of it containing respectively 0.1 g, 0.01 g, and 0.001 g (or 0.1 mL, 0.01 mL, and 0.001 mL) of the product to be examined. Incubate at 30 to 35 for 24 to 48 hours. Subculture each of the cultures on a plate of Violet Red Bile Glucose Agar. Incubate at 30 to 35 for 18 to 24 hours.
Interpretation— Growth of colonies constitutes a positive result. Note the smallest quantity of the product that gives a positive result and the largest quantity that gives a negative result. Determine from Table 2 the probable number of bacteria.
Table 2. Interpretation of Results
Results for Each Quantity
of Product
 
0.1 g or
0.1 mL
0.01 g or
0.01 mL
0.001 g or
0.001 mL
Probable Number
of Bacteria per g
or mL of Product
+ + + more than 103
+ + less than 103 and more
than 102
+ less than 102 and more
than 10
less than 10
Escherichia coli
Sample Preparation and Pre-Incubation— Prepare a sample using a 1 in 10 dilution of not less than 1 g of the product to be examined as described in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61, and use 10 mL or the quantity corresponding to 1 g or 1 mL, to inoculate a suitable amount (determined as described under Suitability of the Test Method) of Soybean–Casein Digest Broth, mix, and incubate at 30 to 35 for 18 to 24 hours.
Selection and Subculture— Shake the container, transfer 1 mL of Soybean–Casein Digest Broth to 100 mL of MacConkey Broth, and incubate at 42 to 44 for 24 to 48 hours. Subculture on a plate of MacConkey Agar at 30 to 35 for 18 to 72 hours.
Interpretation— Growth of colonies indicates the possible presence of E. coli. This is confirmed by identification tests.
The product complies with the test if no colonies are present or if the identification tests are negative.
Salmonella
Sample Preparation and Pre-Incubation— Prepare the product to be examined as described in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61, and use the quantity corresponding to not less than 10 g or 10 mL to inoculate a suitable amount (determined as described under Suitability of the Test Method) of Soybean–Casein Digest Broth, mix, and incubate at 30 to 35 for 18 to 24 hours.
Selection and Subculture— Transfer 0.1 mL of Soybean–Casein Digest Broth to 10 mL of Rappaport Vassiliadis Salmonella Enrichment Broth, and incubate at 30 to 35 for 18 to 24 hours. Subculture on plates of Xylose Lysine Deoxycholate Agar. Incubate at 30 to 35 for 18 to 48 hours.
Interpretation— The possible presence of Salmonella is indicated by the growth of well-developed, red colonies, with or without black centers. This is confirmed by identification tests.
The product complies with the test if colonies of the types described are not present or if the confirmatory identification tests are negative.
Pseudomonas aeruginosa
Sample Preparation and Pre-Incubation— Prepare a sample using a 1 in 10 dilution of not less than 1 g of the product to be examined as described in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61, and use 10 mL or the quantity corresponding to 1 g or 1 mL to inoculate a suitable amount (determined as described under Suitability of the Test Method) of Soybean–Casein Digest Broth, and mix. When testing transdermal patches, filter the volume of sample corresponding to one patch of the preparation (see Transdermal Patches under Preparation of the Sample in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61) through a sterile filter membrane, and place in 100 mL of Soybean–Casein Digest Broth. Incubate at 30 to 35 for 18 to 24 hours.
Selection and Subculture— Subculture on a plate of Cetrimide Agar, and incubate at 30 to 35 for 18 to 72 hours.
Interpretation— Growth of colonies indicates the possible presence of P. aeruginosa. This is confirmed by identification tests.
The product complies with the test if colonies are not present or if the confirmatory identification tests are negative.
Staphylococcus aureus
Sample Preparation and Pre-Incubation— Prepare a sample using a 1 in 10 dilution of not less than 1 g of the product to be examined as described in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61, and use 10 mL or the quantity corresponding to 1 g or 1 mL to inoculate a suitable amount (determined as described under Suitability of the Test Method) of Soybean–Casein Digest Broth, and homogenize. When testing transdermal patches, filter the volume of sample corresponding to one patch of the preparation (see Transdermal Patches under Preparation of the Sample in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61) through a sterile filter membrane, and place in 100 mL of Soybean–Casein Digest Broth. Incubate at 30 to 35 for 18 to 24 hours.
Selection and Subculture— Subculture on a plate of Mannitol Salt Agar, and incubate at 30 to 35 for 18 to 72 hours.
Interpretation— The possible presence of S. aureus is indicated by the growth of yellow or white colonies surrounded by a yellow zone. This is confirmed by identification tests.
The product complies with the test if colonies of the types described are not present or if the confirmatory identification tests are negative.
Clostridia
Sample Preparation and Heat Treatment— Prepare a sample using a 1 in 10 dilution (with a minimum total volume of 20 mL) of not less than 2 g or 2 mL of the product to be examined as described in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61. Divide the sample into two portions of at least 10 mL. Heat one portion at 80 for 10 minutes, and cool rapidly. Do not heat the other portion.
Selection and Subculture— Use 10 mL or the quantity corresponding to 1 g or 1 mL of the product to be examined of both portions to inoculate suitable amounts (determined as described under Suitability of the Test Method) of Reinforced Medium for Clostridia. Incubate under anaerobic conditions at 30 to 35 for 48 hours. After incubation, make subcultures from each container on Columbia Agar, and incubate under anaerobic conditions at 30 to 35 for 48 to 72 hours.
Interpretation— The occurrence of anaerobic growth of rods (with or without endospores) giving a negative catalase reaction indicates the presence of Clostridia.
This is confirmed by identification tests. The product complies with the test if colonies of the types described are not present or if the confirmatory identification tests are negative.
Candida albicans
Sample Preparation and Pre-Incubation— Prepare the product to be examined as described in Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests 61, and use 10 mL or the quantity corresponding to not less than 1 g or 1 mL, to inoculate 100 mL of Sabouraud Dextrose Broth, and mix. Incubate at 30 to 35 for 3 to 5 days.
Selection and Subculture— Subculture on a plate of Sabouraud Dextrose Agar, and incubate at 30 to 35 for 24 to 48 hours.
Interpretation— Growth of white colonies may indicate the presence of C. albicans. This is confirmed by identification tests.
The product complies with the test if such colonies are not present or if the confirmatory identification tests are negative.

RECOMMENDED SOLUTIONS AND CULTURE MEDIA
Note—This section is given for information.
The following solutions and culture media have been found satisfactory for the purposes for which they are prescribed in the test for microbial contamination in the Pharmacopeia. Other media may be used provided that their suitability can be demonstrated.
Stock Buffer Solution— Transfer 34 g of potassium dihydrogen phosphate to a 1000-mL volumetric flask, dissolve in 500 mL of Purified Water, adjust with sodium hydroxide to a pH of 7.2 ± 0.2, add Purified Water to volume, and mix. Dispense in containers, and sterilize. Store at a temperature of 2 to 8.
Phosphate Buffer Solution pH 7.2— Prepare a mixture of Purified Water and Stock Buffer Solution (800:1 v/v), and sterilize.
Buffered Sodium Chloride–Peptone Solution pH 7.0
Potassium Dihydrogen Phosphate 3.6 g
Disodium Hydrogen Phosphate Dihydrate 7.2 g (equivalent to 0.067 M phosphate)
Sodium Chloride 4.3 g
Peptone (meat or casein) 1.0 g
Purified Water 1000 mL
Sterilize in an autoclave using a validated cycle.
Soybean–Casein Digest Broth
Pancreatic Digest of Casein 17.0 g
Papaic Digest of Soybean 3.0 g
Sodium Chloride 5.0 g
Dibasic Hydrogen Phosphate 2.5 g
Glucose Monohydrate 2.5 g
Purified Water 1000 mL
Adjust the pH so that after sterilization it is 7.3 ± 0.2 at 25. Sterilize in an autoclave using a validated cycle.
Soybean–Casein Digest Agar
Pancreatic Digest of Casein 15.0 g
Papaic Digest of Soybean 5.0 g
Sodium Chloride 5.0 g
Agar 15.0 g
Purified Water 1000 mL
Adjust the pH so that after sterilization it is 7.3 ± 0.2 at 25. Sterilize in an autoclave using a validated cycle.
Sabouraud Dextrose Agar
Dextrose 40.0 g
Mixture of Peptic Digest of Animal Tissue and Pancreatic Digest of Casein (1:1) 10.0 g
Agar 15.0 g
Purified Water 1000 mL
Adjust the pH so that after sterilization it is 5.6 ± 0.2 at 25. Sterilize in an autoclave using a validated cycle.
Potato Dextrose Agar
Infusion from potatoes 200 g
Dextrose 20.0 g
Agar 15.0 g
Purified Water 1000 mL
Adjust the pH so that after sterilization it is 5.6 ± 0.2 at 25. Sterilize in an autoclave using a validated cycle.
Sabouraud Dextrose Broth
Dextrose 20.0 g
Mixture of Peptic Digest of Animal Tissue and Pancreatic Digest of Casein (1:1) 10.0 g
Purified Water 1000 mL
Adjust the pH so that after sterilization it is 5.6 ± 0.2 at 25. Sterilize in an autoclave using a validated cycle.
Enterobacteria Enrichment Broth Mossel
Pancreatic Digest of Gelatin 10.0 g
Glucose Monohydrate 5.0 g
Dehydrated Ox Bile 20.0 g
Potassium Dihydrogen Phosphate 2.0 g
Disodium Hydrogen Phosphate Dihydrate 8.0 g
Brilliant Green 15 mg
Purified Water 1000 mL
Adjust the pH so that after heating it is 7.2 ± 0.2 at 25. Heat at 100 for 30 minutes, and cool immediately.
Violet Red Bile Glucose Agar
Yeast Extract 3.0 g
Pancreatic Digest of Gelatin 7.0 g
Bile Salts 1.5 g
Sodium Chloride 5.0 g
Glucose Monohydrate 10.0 g
Agar 15.0 g
Neutral Red 30 mg
Crystal Violet 2 mg
Purified Water 1000 mL
Adjust the pH so that after heating it is 7.4 ± 0.2 at 25. Heat to boiling; do not heat in an autoclave.
MacConkey Broth
Pancreatic Digest of Gelatin 20.0 g
Lactose Monohydrate 10.0 g
Dehydrated Ox Bile 5.0 g
Bromocresol Purple 10 mg
Purified Water 1000 mL
Adjust the pH so that after sterilization it is 7.3 ± 0.2 at 25. Sterilize in an autoclave using a validated cycle.
MacConkey Agar
Pancreatic Digest of Gelatin 17.0 g
Peptones (meat and casein) 3.0 g
Lactose Monohydrate 10.0 g
Sodium Chloride 5.0 g
Bile Salts 1.5 g
Agar 13.5 g
Neutral Red 30.0 mg
Crystal Violet 1 mg
Purified Water 1000 mL
Adjust the pH so that after sterilization it is 7.1 ± 0.2 at 25. Boil for 1 minute with constant shaking, then sterilize in an autoclave using a validated cycle.
Rappaport Vassiliadis Salmonella Enrichment Broth
Soya Peptone 4.5 g
Magnesium Chloride Hexahydrate 29.0 g
Sodium Chloride 8.0 g
Dipotassium Phosphate 0.4 g
Potassium Dihydrogen Phosphate 0.6 g
Malachite Green 0.036 g
Purified Water 1000 mL
Dissolve, warming slightly. Sterilize in an autoclave using a validated cycle, at a temperature not exceeding 115. The pH is to be 5.2 ± 0.2 at 25 after heating and autoclaving.
Xylose Lysine Deoxycholate Agar
Xylose 3.5 g
l-Lysine 5.0 g
Lactose Monohydrate 7.5 g
Sucrose 7.5 g
Sodium Chloride 5.0 g
Yeast Extract 3.0 g
Phenol Red 80 mg
Agar 13.5 g
Sodium Deoxycholate 2.5 g
Sodium Thiosulfate 6.8 g
Ferric Ammonium Citrate 0.8 g
Purified Water 1000 mL
Adjust the pH so that after heating it is 7.4 ± 0.2 at 25. Heat to boiling, cool to 50, and pour into Petri dishes. Do not heat in an autoclave.
Cetrimide Agar
Pancreatic Digest of Gelatin 20.0 g
Magnesium Chloride 1.4 g
Dipotassium Sulfate 10.0 g
Cetrimide 0.3 g
Agar 13.6 g
Purified Water 1000 mL
Glycerol 10.0 mL
Heat to boiling for 1 minute with shaking. Adjust the pH so that after sterilization it is 7.2 ± 0.2 at 25. Sterilize in an autoclave using a validated cycle.
Mannitol Salt Agar
Pancreatic Digest of Casein 5.0 g
Peptic Digest of Animal Tissue 5.0 g
Beef Extract 1.0 g
d-Mannitol 10.0 g
Sodium Chloride 75.0 g
Agar 15.0 g
Phenol Red 0.025 g
Purified Water 1000 mL
Heat to boiling for 1 minute with shaking. Adjust the pH so that after sterilization it is 7.4 ± 0.2 at 25. Sterilize in an autoclave using a validated cycle.
Reinforced Medium for Clostridia
Beef Extract 10.0 g
Peptone 10.0 g
Yeast Extract 3.0 g
Soluble Starch 1.0 g
Glucose Monohydrate 5.0 g
Cysteine Hydrochloride 0.5 g
Sodium Chloride 5.0 g
Sodium Acetate 3.0 g
Agar 0.5 g
Purified Water 1000 mL
Hydrate the agar, and dissolve by heating to boiling with continuous stirring. If necessary, adjust the pH so that after sterilization it is about 6.8 ± 0.2 at 25. Sterilize in an autoclave using a validated cycle.
Columbia Agar
Pancreatic Digest of Casein 10.0 g
Meat Peptic Digest 5.0 g
Heart Pancreatic Digest 3.0 g
Yeast Extract 5.0 g
Maize Starch 1.0 g
Sodium Chloride 5.0 g
Agar, according to gelling power 10.0–15.0 g
Purified Water 1000 mL
Hydrate the agar, and dissolve by heating to boiling with continuous stirring. If necessary, adjust the pH so that after sterilization it is 7.3 ± 0.2 at 25. Sterilize in an autoclave using a validated cycle. Allow to cool to 45 to 50; add, where necessary, gentamicin sulfate corresponding to 20 mg of gentamicin base, and pour into Petri dishes.
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