TESTING
indicative and inhibitory properties. Also utilized in the test(s) are validated
chemical neutralizers at dilution ratios confirmed to inhibit antimicrobial activity present in the sample (e.g. the presence of chemical preservatives). The pathway through which these properties are validated is referred to as suitability testing or method validation. Alternative testing methods can include
DNA and RNA detection/identification, antibody-based detection, rapid biochemical/ metabolic detection/identification, and other quantitative detection methods that may require specialized equipment. Alternative methods of testing are in various stages of development and implementation, and are often specialized and associated with higher costs than traditional, culture-based testing methods.16 Procedures for microbiological limits
testing and applicable suitability controls are summarized herein from harmonized methods in the United States Pharmacopeia (USP) chapters <61> and <62>, European Pharmacopeia (EP) 2.6.12 and 2.6.13., and ISO 21149 and 18415.17-22
Quantitative test limits Quantitative limit tests are performed via sample enumeration; for this reason, they are often referred to as microbial count, total plate count, total viable count, or similar. In this design, a representative sample of product is plated to permissive solid media to recover
any bacteria, yeasts, or moulds present. Enumeration plates are incubated in
optimal growth conditions for a prescribed duration, then evaluated so that the total number of colony-forming units (CFU) per millilitre or gram of test material can be calculated.
Qualitative limit tests Qualitative limit tests are performed via sample enrichment and subculture. The first step, enrichment, mirrors the quantitative test in that a representative sample of product is transferred to permissive media; however, in this context it is liquid media that will support exponential reproduction of any microorganisms present. The enrichment step will allow for detection
of specified objectionable organisms, even if present at a low concentration – it should be noted that it is possible for a product to fail qualitative criteria for microbiological limits testing even if quantitative assessments demonstrate conformance. The enrichment step is followed by
a subculture step, in which media with selective and/or differential properties to screen for specific organisms of interest is implemented. Growth media containing a selective component will prevent growth of non-target organisms and/or cause indicative morphological reactions based on biochemical characteristics: for example, the high salt content of Mannitol salt agar will inhibit
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growth of many organisms incidental to Staphylococci that cannot tolerate such stress conditions Further, fermentation of sugars in the
agar by different strains of Staphylococci will result in characteristic visual morphologies so that, for instance, Staphylococcus aureus can be distinguished from Staphylococcus epidermidis. Most qualitative screening tests use a similar combination of selective and differential factors to demonstrate whether recovered organisms represent those identified as objectionable. Organisms may be categorized as
objectionable where their presence in a formulation poses an increased risk to the consumer. While this may vary on a product- to-product basis, references such as the ISO 17516 propose that cosmetic products demonstrate absence of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans. Complementary to microbiological limits
testing is the assessment of preservative efficacy, or preservative efficacy testing (PET). Preservative efficacy is assessed by challenging products via the introduction of microorganisms representative of contamination that products may be exposed to during manufacture, transport, and regular use.
Typically, Staphylococcus aureus,
Escherichia coli, Pseudomonas aeruginosa, Candida albicans, and Aspergillus brasiliensis
www.personalcaremagazine.com
May 2024 PERSONAL CARE
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