Challenge testing: principles and practice

Microbiological Quality Assessment of Skin and Body care Cosmetics by using Challenge test

Cosmetic products may be exposed to microbial contamination during storage or transport, and to avoid the risk of microbial growth, manufacturers add preservative compounds as a protection for the product from spoilage. The Microbial Challenge test is a procedure to evaluate the preservative efficacy by challenging the product with testing microorganisms to determine the quality of preservation. In this study, thirty-two cosmetics products used for body and skin care were collected from markets and pharmacies in Mecca region, these products are subjected to microbiological analysis, results show that most samples are contaminated except six samples. Non contaminated samples were subjected to European Pharmacopeia 7.0 standards. Results show that two samples, foaming gel and body and face cream are failed to demonstrate the required microbiocidal effect against the S.aureus test species, results recorded 1.21 x 105 and 6.80 x 105 (CFU/ml) respectively at the second day of incubation, other products: shower gel, hand wash, body lotion and shampoo demonstrate that required microbiocidal effect against the test species during day 2, 7, 14 until day 28th. The microbial count number is less than 10 during all incubation periods. To prevent contamination in cosmetics, manufacturers are required to add a good preservative system to the products and examine them before sale. Due to the high percentage of microbial contamination in cosmetics in Mecca region and for consumers safety, this study is prepared.

Challenge Test as Special Tool to Estimate the Dynamic of Listeria monocytogenes and Other Foodborne Pathogens

Over 23 million cases of foodborne disease (FBD) occur in Europe each year, with over 4700 deaths. Outbreaks of FBD have a significant impact on our society due to the high economic losses they cause (hospital treatment of affected patients and destruction of contaminated food). Among its health objectives, the European Union has set itself the goal of reducing the incidence of the main FBDs, approving various regulations that codify requirements in order to produce food that is “safe” for human consumption. Among these rules, Regulation 2005/2073 establishes precise food safety criteria for foods that are judged to be most at risk of causing episodes of FBD. The food business operator (FBO) must know their food better and know how to estimate whether a food can support the growth of food pathogens or if they are able to hinder it during the food’s shelf life. It is becoming crucial for each FBO to schedule specific laboratory tests (challenge tests) to establish the growth potential of individual pathogens and their maximum growth rate. In 2008 the European Union published the guidelines for programming the challenge tests for Listeria monocytogenes in RTE foods. These guidelines were further implemented in 2014 and again in 2019. In June 2019 the UNI EN ISO 20976-1 was published, which contains indications for setting up and carrying out challenge tests for all foodborne pathogens in all foods. In this article, we compare the three official documents to highlight their common aspects and differences, highlighting the advantages and disadvantages that each of them offers for those who have to set up a challenge test for the various foodborne pathogens. Our conclusion is that the challenge test is today the most effective tool to estimate the dynamics and growth potential of pathogenic microorganisms in food, if it is designed and implemented in a scrupulous way. It is important to develop a rational experimental design for each challenge test, and for each food, and this requires professionals who are experts in this specific field of study and who must be properly trained.

Why Are Wet Wipes So Difficult to Preserve? Understanding the Intrinsic Causes

Over the last two decades, significant advances have been made in developing disposable baby wet wipes. Wet wipes consist of two main components: nonwoven fabric and liquid. Being more than 90% water, wet wipes are more susceptible to microbial growth than typical personal care products; hence, high concentrations of preservative compounds are often used to ensure extended protection against contamination. However, there is an obvious tendency to minimize the concentration of irritating actives. Baby wet wipes should contain particularly mild surfactants, well-tolerated preservatives, and a buffer system maintaining the formulation pH at a suitable level for the infant’s skin. Efforts have been centered on removing ingredients with irritation potential, such as phenoxyethanol. In addition, a move towards more natural fabrics is occurring. However, these modifications provoke new challenges in preserving the final products. The nature and composition of the fiber can influence the interactions between the preservative and the wipe, subsequently affecting the performance of the preservative system. In this study, we analyzed the causes of the challenge in preserving wet wipes. We found that fabrics containing natural fibers are the main source of contamination, promoting the generation of biofilms on their surfaces. Moreover, the hydrophilic–lipophilic balance (HLB) was utilized to rationalize the physicochemical interactions between the fabric and the preservatives.

Construction and evaluation of a bioluminescent Pseudomonas aeruginosa reporter for use in preservative efficacy testing

Preservative efficacy testing (PET) is a fundamental practice in industrial microbiology used to ensure product shelf-life and quality. To improve on current growth-based PET, bioluminescence was evaluated as a real-time bacterial viability indicator using Pseudomonas aeruginosa. Random mutagenesis of an industrial P. aeruginosa strain with a promoter-less luxCDABE mini-Tn5 was used to select a stable reporter (LUX12H5) with an un-altered growth and preservative susceptibility phenotype. Bioluminescence and viability were measured with and without preservatives (isothiazolinones, phenoxyethanol, and dimethyl dimethylol hydantoin) and an antibiotic comparator (ciprofloxacin). In the absence of antimicrobials, a good correlation between bioluminescence and viability (r2=0.92) was established. However, metabolic inhibition by isothiazolinone preservatives caused a rapid decline in light output that did not correlate to a reduced viability. Conversely, after ciprofloxacin exposure, the decline in viability was greater than that of bioluminescence. A positive attribute of the bioluminescence was the early detection of metabolic recovery and re-growth of preservative injured bacteria. Overall, while initial bioluminescence read-outs were less suited to current PET requirements, it shows promise as an early, direct indicator of bacterial regrowth in the context of long-term evaluation of preservative efficacy.

The Use of Catalytic Amounts of Selected Cationic Surfactants in the Design of New Synergistic Preservative Solutions

Preservation using combinations of antibacterial molecules has several advantages, such as reducing the level of usage and broadening their antimicrobial spectrum. More specifically, the use of quaternary ammonium surfactants (QAS)—which are profusely used in hair care products and some are known as efficient antimicrobial agents—is limited due to some potential cytotoxicity concerns. This study shows that the concentration of some widely used cosmetic preservatives can be decreased when combined with very small quantities of QAS, i.e., Polyquaternium-80 (P-80) and/or Didecyldimethylammonium chloride (DDAC). The antimicrobial activity of their mixtures was first evaluated by determining the minimum inhibitory concentration (MIC) before and after the addition of QAS. Following up on this finding and targeting an ultimate consumer friendly antimicrobial blend, yet with optimal safety, we chose to utilize the food-grade preservative Maltol as the main natural origin antimicrobial agent mixed with minimum concentrations of QAS to improve its moderate antimicrobial properties. The preservatives were tested for MIC values, challenge tests and synergy using the fractional inhibitory concentration index (FICI). The antimicrobial efficacy of Maltol was found to be synergistically improved by introducing catalytic amounts of P-80 and/or DDAC.

Rapid assessment and prediction of the efficiency of two preservatives against S. aureus in cosmetic products using High Content Screening-Confocal Laser Scanning Microscopy

Most cosmetic products are susceptible to microbiological spoilage due to contaminations that could happen during fabrication or by consumer’s repetitive manipulation. The composition of cosmetic products must guarantee efficient bacterial inactivation all along with the product shelf life, which is usually assessed by challenge-tests. A challenge-test consists in inoculating specific bacteria, i.e. Staphylococcus aureus, in the formula and then investigating the bacterial log reduction over time. The main limitation of this method is relative to the time-consuming protocol, where 30 days are needed to obtain results. In this study, we have proposed a rapid alternative method coupling High Content Screening—Confocal Laser Scanning Microscopy (HCS-CLSM), image analysis and modeling. It consists in acquiring real-time S. aureus inactivation kinetics on short-time periods (typically 4h) and in predicting the efficiency of preservatives on longer scale periods (up to 7 days). The action of two preservatives, chlorphenesin and benzyl alcohol, was evaluated against S. aureus at several concentrations in a cosmetic matrix. From these datasets, we compared two secondary models to determine the logarithm reduction time (Dc) for each preservative concentration. Afterwards, we used two primary inactivation models to predict log reductions for up to 7 days and we compared them to observed log reductions. The IQ model better fits datasets and the Q value gives information about the matrix level of interference.

Top-down evaluation of the matrix effects in microbial enumeration test uncertainty

Microbial contamination may compromise the efficacy and safety of pharmaceutical products. Microbial enumeration tests are required by most of the pharmacopeial compendia and consist in conventional pour-plate inoculation of a sample aliquot followed by incubation under appropriate conditions. Despite of this, the measurement uncertainty evaluation for microbial enumeration tests is rarely considered. Thus, the aim of this paper was to assess the matrix effects in microbial enumeration tests and their top-down uncertainty evaluation. Microbial counting methods for eighteen pharmaceutical products were validated concerning the trueness (mean recovery) and precision (repeatability and intermediate precision) using seven test microorganisms. Uncertainty factors values were found to be between 1.1 and 3.3, based on trueness and precision results. Trueness uncertainty component was the most relevant in 59% of the cases. This issue can be explained due to the matrix interference cause by preservatives or antimicrobial agents, particularly for lower dilutions when compared to higher dilutions. Thus, we concluded that the higher the matrix interference the higher the uncertainty factor, and consequently, the higher the asymmetry for the interval around the measurement.

Bactericidal and Cytotoxic Properties of Silver Nanoparticles

Silver nanoparticles (AgNPs) can be synthesized from a variety of techniques including physical, chemical and biological routes. They have been widely used as nanomaterials for manufacturing cosmetic and healthcare products, antimicrobial textiles, wound dressings, antitumor drug carriers, etc. due to their excellent antimicrobial properties. Accordingly, AgNPs have gained access into our daily life, and the inevitable human exposure to these nanoparticles has raised concerns about their potential hazards to the environment, health, and safety in recent years. From in vitro cell cultivation tests, AgNPs have been reported to be toxic to several human cell lines including human bronchial epithelial cells, human umbilical vein endothelial cells, red blood cells, human peripheral blood mononuclear cells, immortal human keratinocytes, liver cells, etc. AgNPs induce a dose-, size- and time-dependent cytotoxicity, particularly for those with sizes ≤10 nm. Furthermore, AgNPs can cross the brain blood barrier of mice through the circulation system on the basis of in vivo animal tests. AgNPs tend to accumulate in mice organs such as liver, spleen, kidney and brain following intravenous, intraperitoneal, and intratracheal routes of administration. In this respect, AgNPs are considered a double-edged sword that can eliminate microorganisms but induce cytotoxicity in mammalian cells. This article provides a state-of-the-art review on the synthesis of AgNPs, and their applications in antimicrobial textile fabrics, food packaging films, and wound dressings. Particular attention is paid to the bactericidal activity and cytotoxic effect in mammalian cells.

Cosmetics Preservation: A Review on Present Strategies

Cosmetics, like any product containing water and organic/inorganic compounds, require preservation against microbial contamination to guarantee consumer’s safety and to increase their shelf-life. The microbiological safety has as main goal of consumer protection against potentially pathogenic microorganisms, together with the product’s preservation resulting from biological and physicochemical deterioration. This is ensured by chemical, physical, or physicochemical strategies. The most common strategy is based on the application of antimicrobial agents, either by using synthetic or natural compounds, or even multifunctional ingredients. Current validation of a preservation system follow the application of good manufacturing practices (GMPs), the control of the raw material, and the verification of the preservative effect by suitable methodologies, including the challenge test. Among the preservatives described in the positive lists of regulations, there are parabens, isothiasolinone, organic acids, formaldehyde releasers, triclosan, and chlorhexidine. These chemical agents have different mechanisms of antimicrobial action, depending on their chemical structure and functional group’s reactivity. Preservatives act on several cell targets; however, they might present toxic effects to the consumer. Indeed, their use at high concentrations is more effective from the preservation viewpoint being, however, toxic for the consumer, whereas at low concentrations microbial resistance can develop.

Methanol extracts from the resurrection plant Haberlea rhodopensis ameliorate cellular vitality in chronologically ageing Saccharomyces cerevisiae cells

Bioactive substances that are found in many natural plant extracts are very important for the cosmetics, pharmaceutical industry and biotechnology. Especially interesting for these industries are the substances that possess cell revitalizing and anti-ageing properties. The endemic plant Haberlea rhodopensis is known for its ability to withstand drought and to revitalize when returned to optimal conditions after a long time in desiccation. It is a mere fact that this plant not only can completely resurrect from a dried state but is also able to bring back the natural biochemical compositions of its cells. As a result H. rhodopensis offers a wide field for investigation of the exact mechanisms of the revitalization process as well as broadens the search for unique bioactive chemical substances in its cells. Here, by using the yeast Saccharomyces cerevisiae as a model we have demonstrated that methanol extracts from the plant H. rhodopensis hold specific properties to revitalize and ameliorate cellular growth as well as to balance intracellular metabolic states. Our results add valuable knowledge on the effects of natural compounds on ageing and reinforce the idea of using yeast as a model organism in the development of rapid tests for studying the efficacy of different bioactive substances.

An innovative challenge test for solid cosmetics using freeze-dried microorganisms and electrical methods

Freeze-dried bacteria and fungi were used as inoculum in 28 days' PET. An electrical method was used in replacement of the conventional plate count method. The use of freeze-dried microorganisms in association with the electrical method can minimize the workload and the variability involved in PET for cosmetic powders.

Emergence of resistance to antibacterial agents: the role of quaternary ammonium compounds--a critical review

Quaternary ammonium compounds (QACs) are widely distributed in hospitals, industry and cosmetics. Little attention has been focused on the potential impact of QACs on the emergence of antibiotic resistance in patients and the environment. To assess this issue, we conducted a literature review on QAC chemical structure, fields of application, mechanism of action, susceptibility testing, prevalence, and co- or cross-resistance to antibiotics. Special attention was paid to the effects of QACs on microflora; in particular, the issue of the potential of QACs for applying selective pressure on multiple-antibiotic-resistant organisms was raised. It was found that there is a lack of standardised procedures for interpreting susceptibility test results. QACs have different impacts on the minimum inhibitory concentrations of antibacterials depending on the antibacterial compound investigated, the resistance genes involved, the measuring methodology and the interpretative criteria. The unmet needs for adequate detection of reduced susceptibility to QACs and antibiotics include (i) a consensus definition for resistance, (ii) epidemiological cut-off values and (iii) clinical resistance breakpoints. This review advocates the design of international guidelines for QAC use.

Development and validation of a microbial counting method for mebendazole oral suspension

Mebendazole is an important medicine used to treat helminth infections. These infections affect more than two billion people worldwide. The LAFEPE® (Recife-PE, Brazil) produces the drug mebendazole oral suspension that contains the preservatives methylparaben and propylparaben in its formulation. Drugs that have antimicrobial properties due to preservatives must undergo neutralization of these compounds to allow microbial count testing according to recommendations by the official compendia. In order to obtain a validated method for microbial counting and to ensure its safety and reliability within the pharmaceutical industry, validation of preservative neutralization and of the method for microbial counting was performed according to the USP 30 and PDA Technical Report No. 33. The method used ATCC Gram positive and Gram negative microorganisms, yeasts, most and culture media Tryptic Soy Agar and Sabouraud dextrose agar. The neutralizers were polysorbate 80 and lecithin. Recovery levels of over 70% of the microorganisms used in the test indicated the neutralization of antimicrobial activity and proved the absence of toxicity of neutralizers. The microbial counting method validated proved accurate, precise, robust and linear and can be safely used in routine operations.

Inappropriate use of D-values for determining biocidal activity of various antimicrobials

The objective of this study was to investigate the application of established D-value calculations to survival curves for various bacteria using the following antimicrobials: acidified sodium chlorite, triclosan, octanoic acid, and sodium hydroxide. D-values can be calculated in 3 ways, a linear regression, an endpoint calculation, or an average of multiple endpoint calculations. The assumption made in calculating a D-value is that the rate of kill follows 1st-order kinetics under specified treatment conditions. Each antimicrobial solution was challenged with approximately 108 CFU/mL of Staphylococcus aureus, Listeria monocytogenes, Salmonella enterica subsp. enterica, and Escherichia coli independently and in triplicate. Test systems were sampled at each of the 10 time points over a period of 7 min, neutralized, pour plated then incubated at 35 °C for 48 h (AOAC official method 960.09). Survival curves using the log-transformed data were calculated using regression analysis. Correlations coefficients for all linear regression analyses ranged between 0.291 and 0.982, with 6 of the 16 different treatment systems having an R2 value below 0.7. Methods used for calculating D-values should lead to the same result if the survival curve in a given condition is linear. The calculated D-values were different using endpoint analysis (Stumbo method), linear regression, and average of multiple endpoints. This study demonstrates the nonlinearity of inactivation curves of antimicrobials. D-value estimations cannot be reliably used to illustrate biocidal activity in antimicrobial test systems.

Does the wide use of quaternary ammonium compounds enhance the selection and spread of antimicrobial resistance and thus threaten our health?

Quaternary ammonium compounds (QACs) are widely used biocides that possess antimicrobial effect against a broad range of microorganisms. These compounds are used for numerous industrial purposes, water treatment, antifungal treatment in horticulture, as well as in pharmaceutical and everyday consumer products as preserving agents, foam boosters, and detergents. Resistance toward QACs is widespread among a diverse range of microorganisms and is facilitated by several mechanisms such as modifications in the membrane composition, expression of stress response and repair systems, or expression of efflux pump genes. Development of resistance in both pathogenic and nonpathogenic bacteria has been related to application in human medicine and the food industry. QACs in cosmetic products will inevitably come into intimate contact with the skin or mucosal linings in the mouth and thus are likely to add to the selection pressure toward more QAC-resistant microorganisms among the skin or mouth flora. There is increasing evidence of coresistance and cross-resistance between QACs and a range of other clinically important antibiotics and disinfectants. Use of QACs may have driven the fixation and spread of certain resistance cassette collectors (class 1 integrons), currently responsible for a major part of antimicrobial resistance in gram-negative bacteria. More indiscriminate use of QACs such as in cosmetic products may drive the selection of further new genetic elements that will aid in the persistence and spread of antimicrobial resistance and thus in limiting our treatment options for microbial infections.

Preservative efficacy screening of pharmaceutical formulations using ATP bioluminescence

The preservative challenge test is a method used to determine the efficacy of a preservation system in a pharmaceutical or cosmetic formulation. However, such testing is a labor-intensive, repetitive task often requiring days before results can be generated. Several alternatives to traditional colony-count techniques have been developed. A study using pure suspensions of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Bacillus subtilis, Candida albicans, and Aspergillus niger showed that the accuracy, repeatability, and linearity of the Pallchek luminometer ATP bioluminescence (ATP-B) system was equivalent to the traditional colony-count method. In any case, the method proved sensitive enough to follow the effect of preservatives on a number of test microorganisms, indicating the applicability of the ATP-B method for preservative screening studies in various pharmaceutical formulations.

Investigation of Product Quality Between Extemporaneously Compounded Progesterone Vaginal Suppositories and an Approved Progesterone Vaginal Gel

The purpose of this investigation was to compare quality parameters, including product appearance, content uniformity, pH, weight uniformity, microbial limit testing and preservative effectiveness testing on extemporaneously compounded progesterone vaginal suppositories obtained from 10 randomly chosen compounding pharmacies (90 suppositories each) across the United States, to the Food and Drug Administration (FDA) approved prescription progesterone gel product (Prochieve/Crinone) which is manufactured in a cGMP regulated facility. The content uniformity and pH were determined using qualified methods. The microbial limits testing and preservative effectiveness testing were conducted according to compendial methods. Only one pharmacy provided suppositories that were all within the potency limits required for the prescription progesterone gel product. The other pharmacies provided at least some suppositories where progesterone content was either subpotent or superpotent for progesterone. The pH of most of the compounded suppository products was in the range of 4.22 to 7.68 with a median of 6.30 (normal vaginal pH is <5), whereas the gel product was 2.80. For compounded product from one of the pharmacies, microbial limits testing indicated CDC group IVC-2 and Comamonas acidovorans were detected. This data indicates that pharmacy compounded delivery systems for progesterone should be used with caution.