Dirk Bockmühl

Influence of farnesol on the morphogenesis of Aspergillus niger.

Farnesol was the first quorum‐sensing regulator to be found in eukaryotic cells. In Candida albicans, a dimorphic fungal human pathogen, farnesol blocks the yeast‐to‐filamentous growth transition. Here we show that in Aspergillus niger farnesol acts as an inhibitor of conidiation: Colonies grown on media containing farnesol were unable to develop conidia. Although farnesol treated A. niger cultures exhibited a colony morphology resembling the “fluffy” phenotype of A. nidulans, which is caused by a hyperactive G‐protein/cAMP pathway, the intracellular level of cAMP in A. niger mycelia grown in presence of farnesol is greatly diminished. Furthermore, whereas inhibiting adenylyl cyclase led to a farnesol‐like effect, the addition of external cAMP inhibited conidiation without causing a “fluffy” phenotype. This suggests that the mechanisms regulating conidiation in A. niger and A. nidulans are different. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Evaluation of the virucidal performance of domestic laundry procedures

Laundering is one of the most important means to ensure a sufficient hygiene standard in the household environment. To evaluate the performance of this process, it is desirable to have methods that mimic the real-life situation as closely as possible. Although methods for the evaluation of the antibacterial and antifungal efficacy of domestic laundry procedures are available, the effect of laundering on viruses is still rather unclear. As the influence of laundry process parameters such as mechanical actions, temperature dynamics or liquor ratio cannot be simulated in vitro by suspension assays, a new in situ test method allowing virus simulation tests in washing machines has been developed. Using this in situ method we could show that conventional household washing detergents have a full virucidal efficiency at 40 degrees C also against non-enveloped surrogate viruses.

Antimicrobial Efficacy of Hygiene Rinsers under Consumer-Related Conditions

Abstract In domestic laundry, the question how to achieve a sufficient germ reduction gains importance since the trend towards lower washing temperatures and the incremental use of bleach-free liquid detergents does not ensure a sufficient hygiene by the means of temperature and bleach any longer. Hygiene rinsers as products being added to the rinse cycle offer further antimicrobial efficacy and seem to provide an adequate solution for this challenge. However, their regular application is debated due to the used ingredients and it is still unclear whether they are able to exhibit an additional antimicrobial efficacy. This study investigates the germ reduction by a supplementary use of hygiene rinsers under conditions that are close to the parameters found in the household to evaluate the benefit of these products for the hygienic reconditioning of laundry.

Biosurfactants as Antimicrobial Ingredients for Cleaning Products and Cosmetics

Abstract A considerable number of biosurfactants have been investigated for their antibacterial, antifungal or antiviral activity that is mostly based on the ability to destroy microbial cell membranes. In addition, some of them are also able to inhibit the adhesion of microorganisms to surfaces and tissues. Although these antimicrobial properties can be generally explained by a strong detergency effect, there are further mechanisms, such as the interaction with membrane phospholipids or the alteration of the electrical conductance of membranes, resulting in the damage of microbial cells. Typically, antimicrobially active biosurfactants are glycolipids (e.g. rhamnolipids) or cyclic lipopeptides (e.g. Polymyxin). Since most of these substances were not available in larger quantities in the past, their potential applications in cleaners and cosmetics was not studied intensely, however, their versatility and the possibility of combining different properties, such as cleaning and antimicrobial effects, suggest a further consideration of biosurfactants even for mass-market products.

Characterization of Microbial Communities in Household Washing Machines

Abstract Although microbial contaminations of domestic appliances are believed to gain importance, especially due to the trend towards lower cleaning temperatures, little is known about the existing microbial communities inside household washing machines. This study aimed to improve the knowledge of microbial composition of biofilms within household washing machines using a cultural-independent technology. Biofilms inside the detergent drawer and the rubber door seal of household washing machines were analysed using the 454-pyrosequencing method. The microbial community inside washing machines appeared to be highly diverse with Proteobacteria as the main prokaryotic and Basidiomycota and Ascomycota as the main fungal colonizers.

Inactivation of Human Norovirus by Common Domestic Laundry Procedures

Abstract Today, noroviruses (NoV) are the worlds most common cause of human gastroenteritis. Because of its low infectious dose and its ability to persist in the environment, the virus can be easily transmitted from person-to-person. In addition, surfaces like toilet seats, door handles or clothes worn by infected patients might serve as transmission vectors. Although environmental contamination plays a big role in the spread of the virus, little is known about how contaminated surfaces and textiles can be cleaned efficiently to prevent infections. To estimate the lifelike situation, textiles were contaminated with NoV-containing stool and washed in a normal household machine using laundry detergents with or without activated oxygen bleach at different temperatures. The obtained results show that a sufficient inactivation of NoV-contaminated fabric requires a washing temperature of at least 60°C, even if a detergent with activated oxygen bleach is used.

Microbicidal Action of Heat, Detergents and Active Oxygen Bleach as Components of Laundry Hygiene

Abstract It is known that decreasing temperatures in laundry can have a significant impact on the hygiene efficacy of laundering. This study used suspension tests to investigate the microbicidal effects of heat, detergent and activated oxygen bleach and their contributions to laundry hygiene. The results indicate that heat at 60°C contributes significantly to the microbicidal action, while detergent only has limited effects. Activated oxygen bleach strongly enhances the microbicidal action and thus has the potential to compensate for the loss of antimicrobial efficacy due to temperature decrease. This effect varied with the test strain and the temperature, and further work is needed to determine whether it is possible to achieve a hygiene effectiveness equivalent to that at 60°C across both fungal and bacterial strains.

Antimicrobial Efficacy of Laundry Detergents with Regard to Time and Temperature in Domestic Washing Machines

Abstract In times of low-temperature washing, laundry hygiene gains importance, as microbial contaminations on textiles can cause infection transmission and malodour formation. This study systematically investigated the antimicrobial effect of laundry detergents (solid and liquid market detergents) with regard to time and temperature in domestic washing machines. To evaluate the microbial reduction, cotton swatches contaminated with Staph. aureus, Ent. hirae, Ps. aeruginosa, C. albicans and T. mentagrophytes were washed at 20 to 60 °C, varying the washing time, with and without detergent. All tested washing factors affected the antimicrobial effect of to a varying extend, depending on the germ. The used solid market detergent containing activated oxygen bleach provided a way to achieve high microbial reductions in low temperature washing.

Laundry Hygiene and Visible Cleanliness: An Attempt to Predict the Antimicrobial Efficacy of Laundering Processes by its Cleaning Performance

Abstract Insufficiently decontaminated textiles could lead to transmission of infections. Thus, laundry hygiene is of particular interest and investigated in numerous studies. However, laundering experiments that use microorganisms to investigate the reduction of microbial loads on textiles are particularly time-consuming and material-intensive and the handling of pathogenic microorganisms is subject to legal regulations. Therefore, alternative methods of investigation are desired. So far, there is no satisfactory solution to assess the antimicrobial efficacy of a laundering process without expensive microbiological investigations. This study introduces an approach to predict the antimicrobial performance of a laundering process by its cleaning performance. It is not possible to conclude immediately from the cleaning index of a washing process to its antimicrobial effect based on stain types used in this study. Also in washing processes with low cleaning indices a high microbial reduction can be achieved. For bleach free liquid detergent, strong, time dependent, positive correlations between microbial reduction and cleaning index for cocoa, soot, and sebum were identified.

Development of a Test Method for Analyzing the Hygienic Performance of Commercial Dishwashers Operating on the Fresh Water Principle

Abstract In recent years, the aspect of hygiene has become increasingly important in all areas of daily life. Especially in the areas of gastronomy, nursing homes, kindergartens and hospitals, the hygiene aspect is of particular importance. This study deals with the examination of the hygienic performance of commercial dishwashers with a water replacement system (fresh water dishwashers) using Micrococcus luteus DSM 1790 and the carrier material oat flakes as test soil. After rinsing, the soil is detached from the test items using an elution solution. Furthermore, the sump and the back and side walls of the commercial fresh water dishwasher were examined by contact plates to obtain the microbial count. This approach has been tested for functionality in a series of empirical experiments. In addition, the influence of various commercial detergents on results was examined. It was found that the newly developed method emphasizes the difference between the tested programs. Furthermore, it was found that using a program with longer holding times led to a higher germ reduction in the upper basket than in the lower basket.