Wet Wipes from a Microbiological Perspective: A New Preservative Efficacy Test Method

Summary

Wet wipes have become an increasingly popular product used in homes and workplaces in our daily lives. Although initially developed as a personal care product, their successful results have over time led to the development of many products for household care and industrial applications such as cleaning, disinfection and polishing. The preservation of wet wipes is a rather complex matter and requires a unique solution containing combinations of different preservatives to provide complete protection against microbial deterioration. It is critical to select an appropriate test method [1] to ensure the reliability of a test result that can truly predict what may happen in the field after the product is manufactured and brought to market. We are pleased to say that Thor Microbiology Divisions recently developed a test method that produces consistent results. This method provides for multiple inoculation with specific bacterial, yeast and mold species responsible for the deterioration of wet wipes and other consumer products.

Introduction

The approach required to evaluate the microbiological safety of cosmetic products on the market in Europe or imported into the European community is outlined by the two reference documents specified below: Regulation (EC) No. 1223/2009; of the European Parliament and of the Council of 30 November 2009 on cosmetic products [2] Annex I: Cosmetic Product Safety Report Part A – Cosmetic Product Safety Information 3. Microbiological Quality. SCCS's (European Scientific Committee for Consumer Safety) Notes; guidelines for the testing and safety assessment of cosmetic substances 8th Revision [3] regulations on the microbiological quality of finished cosmetic products in section 4-4. According to Regulation (EC) No 1223/2009, the safety report for a cosmetic product must contain at minimum the microbiological characteristics of the substance or mixture and […] the preservative efficacy (challenge) test results of the cosmetic product. Additionally, section 4-4.3 Efficacy (Challenge) Test of the SCCS Notes guidance [based on US Pharmacopoeia 2002, European Pharmacopoeia 2001] states: "The preservative efficacy of a cosmetic product under development shall be evaluated experimentally to confirm that it provides protection with microbiological stability during storage and use. This phase is conducted with a challenge (preservative efficacy) test. Under normal storage and use conditions, products may deteriorate or create a risk of infection in the consumer. For this reason, the preservative efficacy test, which confirms the protection in this process, is mandatory for all cosmetic products. A preservative efficacy test (challenge test) involves artificial contamination of the finished product and subsequent evaluation of the level of reduction in contamination to meet the microbial limits established for categories 1 and 2. The microorganism strains used in the preservative efficacy test may be obtained from any official microorganism strain collection located in Europe to ensure test repeatability. Preservation of wet wipes is difficult and there is no universal preservative system that will cover the preservation of all different types of wipes. There are many critical factors affecting the ultimate preservation of wet wipes against microorganism contamination (Figure 1). Therefore, the determination of an appropriate preservative efficacy test, as much as the selection of the correct preservative to support efficacy, becomes important in this process.

Development of Preservative Efficacy Test Method for Wet Wipes

Before starting on the subject, it may be necessary to provide a complete definition of wet wipe. A wet wipe consists of two parts; a carrier (non-woven) and a liquid solution formulated differently for different applications and impregnated in this non-woven.

Evaluation of Current Methods in the Industry

Thor's technical experts evaluated various test protocols to optimize the existing methodology (Table 1). As is known, to date there is no official standard norm evaluating the preservative efficacy of wet wipe as a finished product. All existing methods are test methods designed and used internally by cosmetic companies or preservative manufacturers. When we compare the results of methods that have existed in the industry for a long time in terms of reproducibility and repeatability, we see that there are significant differences that require attention. In particular, for methods where the test is performed directly on the package, various problems can be identified as summarized below: • Inoculum not being distributed homogeneously within the package, • Inoculum not being in a fully proportional relationship with the weight of the wipes and the package size, • Lack of correlation with the number of wipes in the package, • When bacterial, fungal and yeast strains are mixed for inoculation, organisms competing with each other, • Visual assessment difficulties in petri dishes when organisms are mixed for inoculation, • Different results obtained at the top, middle and bottom of the package due to possible chromatographic effects of the preservative within the package, • Insufficient reproducibility, • Insufficient repeatability. As a result, key findings that could affect the accuracy of test results have been identified. It is also important to be aware that other methods containing a solid carrier or methods in which various microorganisms are tested separately are costly protocols. Some advantages and disadvantages of all these methods were identified and used as a basis for new protocol design.

Identification of Important Key Points for the Method

In the design of a test method, it is first necessary to list and define all relevant points for test accuracy. (Table 2) This article will focus on 3 examples to demonstrate the problems encountered in all these key points:

1. Inoculum Distribution / How Should Inoculation Be Performed?

The test method should be designed to perform inoculation on appropriate portions of the wipes. Consistent distribution along the same wipe is as important as consistent distribution between wipes. Figure 2. Different inoculum distribution approaches are used in existing tests in the industry. Some tests include a physical step to homogeneously distribute microorganisms within wet wipes. If the inoculated amount is very low, this step becomes particularly important. This operation can be performed manually or mechanically. The advantages and disadvantages of each technique are described in Table 3 below: 2. Content of Inoculum Wet wipes are extremely susceptible to microbial contamination. In the preservation of wet wipes, fungal growth (Figure N°3) is often seen as one of the main problems. However, tests show that wet wipes are also susceptible to bacterial growth (Figure N°4), but bacterial contamination is often not noticed because it is generally not visible to the naked eye. Tests should select and include primary microorganisms, not just representatives from microorganism families. Therefore, different organisms or organismal pools should be used but inoculations should always be made separately as bacteria, yeast and mold.

Microorganism Pool Used by Thor Method

3. Acceptance Criteria

Conclusion

Thor microbiologists designed a versatile new test method to evaluate the microbiological safety of wet wipes. This method can be applied without application restrictions to products such as baby wipes, toilet wipes, makeup cleansing wipes, household care products (surface cleaners, skin wipes, car wipes…). As mentioned in Table 4, a general acceptance criterion is selected. One of the main advantages of this method is its flexibility. Additional microorganisms such as domestic microorganisms encountered in operational hygiene can be added. Microbiologists responsible for safety assessment can also easily select different sampling points to adjust the method's results according to their internal Pass/Fail criteria. The challenging goal of developing a safe and repeatable test method has been achieved by going through the above phases. Additionally, the aim was to minimize test costs and maintain sufficient flexibility to satisfy most stakeholders in the wet wipe industry. Dagmar Antoni-Zimmerman Technical Service and Project Manager Biocides and Personal Care     Stéphane Sellam Technical Service and Registration Manager - Personal Care Group         Marta Urizal Comas Biocides and Personal Care Technical Manager         Serap Erbek Personal Care and Detergent Sales Representative    

References [1]-Kevin Roden – The Preservation Of Wet Wipes – Personal Care Magazine – November 2012 [2]-Regulation (EC) No 1223/2009 Of The European Parliament And Of The Council Of 30 November 2009 On Cosmetic Products. [3]-SCCS's Notes Of Guidance For The Testing Of Cosmetic Substances And Their Safety Evaluation 8th Revision.