Cosmetics Testing - Schülke-Koko preservative efficacy (Challenge) test.

Test not accredited in our laboratory.

Test with the certificate of Good Laboratory Practices (GLPs).

Information

There are several types of tests to evaluate the effectiveness of preservatives incorporated into a cosmetic product and European legislation does not specify which of them should be used (Regulation EC No. 1223/2009 of the European Parliament). The most used Challenge tests in our laboratory are the test carried out according to the ISO 11930 standard, or the section 5.1.3 of the European Pharmacopoeia (European Pharmacopoeia). However, there are other tests, such as the Schülke-Koko test. Unlike the analyses described by the pharmacopoeias and the ISO 11930 standard, which use only pathogenic microorganisms, the Schülke-Koko test includes microorganisms that alter and degrade the product. The choice of microorganisms that alter the product is based on decades of experience of the Schülke laboratory in providing assistance to cosmetics manufacturers in the field of microbiological quality management. The Schülke-Koko test also differs in that it uses a mixed inoculum, that it is a semi-quantitative method, that it includes 6 re-inoculations and has a duration of 6 weeks, with weekly evaluations, and finally, in the evaluation criteria that also differ from those indicated by other regulations.

Four microorganisms are used in all preservative efficacy tests: Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Aspergillus brasiliensis. In addition, other microorganisms that can cause alteration of the cosmetic product are usually included (see below). Unlike the European Pharmacopoeia method that uses only pathogenic microorganisms, the Schülke-Koko test includes degrading microorganisms, chosen according to the experience of Schülke´s service to cosmetics manufacturers.

In this test, an inoculum is used with a mixture of microorganisms (unlike tests based on the European Pharmacopoeia and ISO 11930, in which the test microorganisms are inoculated independently) and with a volume, with respect to the inoculated product, of 0.4% per microorganism making a total of 2.4% with the 6 inoculations performed weekly throughout performing the test.

The microorganisms used are: Pluralibacter gergoviae (formerly Enterobacter gergoviae), Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas putida, Burkholderia cepacia, Kocuria rhizophila, Staphylococcus aureus, Candida albicans, Aspergillus niger (syn. Aspergillus brasiliensis), and Talaromyces pinophilus (syn. Penicillium funiculosum or Penicillium pinophilum).

This test is designed to simulate conditions more comparable to the conditions in which a cosmetic product is used. Thus, by inoculating a mixture of microorganisms, it is possible to obtain symbiotic growth similar to that which could occur under natural conditions.

The preserving effect is evaluated semi-quantitatively by the growth of microorganisms on nutritive media when the samples are seeding weekly by the streak plate method. Reductions of test microorganisms are evaluated weekly. If a sample meets criterion A (reduction ≥4 log for bacteria and ≥3 log for fungi), it means that even after the sixth inoculation no microbial growth can be observed, the product can be considered well preserved. Thanks to many years of experience in using this test method, if a product meets criterion A, the microbiological stability of 30 months can be affirmed, which is recommended for cosmetic products. If the formulation meets criterion B (≥3 log reduction for bacteria and ≥2 log for fungi), when only slight growth is detected until 6th cycle, the microbiological risk analysis must demonstrate the existence of control factors unrelated to the formulation; for example, protective packaging and/or following strong requirements for good manufacturing practices.

According to the Schülke-Koko test, an unpreserved sample should be test as a positive control that should show microbial growth. If this sample is not available, the control will be performed with TSB medium.