Laundry Hygiene
Dirk P. Bockmühl
Marlitt Honisch
MICROORGANISMS ON TEXTILESMicrobial contaminations on laundry items originate from numerous sources. During the different stages of the utilization cycle of textiles, various microbial species are introduced to the fabric on the one hand and they are being removed, inactivated, or killed on the other (Figure 46.1). This cycle includes the process of wearing or using a textile followed by its reconditioning (ie, sorting, laundering, drying, and storing). Thus, the presence of microorganisms on textiles is closely linked to their way of use: Microbial contaminants on textiles with narrow body contact, such as clothing and towels, are expected to be predominantly members of the human skin and mucosal biota as well as contaminations that result from bodily excretions. Another source of microbial contamination on textiles that is closely related to their use is the environment, including dust, soil, or food. Moreover, the washing machine itself has been shown to be a source of microbial contaminations being of particular importance in the context of laundering (Table 46.1). Although a major proportion of the microbial cells that are present on a used textile will be removed or inactivated during laundering, microbial biofilms colonizing the detergent distribution system of the washing machine can be detached in the washing process and transported with the rinsing water, resulting in a recontamination of the laundry after the main wash cycle. As a result, the microbial load on the textiles might even increase by laundering.10
In general, it can be assumed that most of the microorganisms found on clothes do not pose an immediate health risk because everybody is in regular contact with them anyway because they are also part of the human microbiome or the environment. However, there are situations where an increased health risk from laundry must be considered (eg, in the case of an infectious disease present in a household or when immunocompromised people are concerned), which is particularly important in the case of domestic health care as well as for care facilities or hospitals. Other situations in which deficient laundry hygiene might pose a health risk include reinfection by insufficiently decontaminated items and the transmission of infections among household members via cross-contamination (ie, the transfer of microbial cells from contaminated to non-contaminated textiles). Consequently, contaminations of facultative or obligatory pathogenic microorganisms on laundry items should be reduced to a noninfectious level as one measure among others to avoid the transmission of infections.
Besides the risk of infection, microbial contaminations on textiles or in washing machines can also cause aesthetic impairments, such as the generation of malodors on washed textiles or the formation of biofilms in the washing machine. Particularly in the domestic environment, the generation of malodors might be considered as one of the most prominent microbiological problems related to laundry.11,12,13,14
It can be assumed that there are two major types of typical laundry-associated malodors: acidic, sweat-like odors on the one hand and musty, “wet-and-dirty-dustcloth-like” odors on the other hand.15 The formation of malodors on washed textiles is thought to be caused by the bacterial metabolization of sweat residues,16 whereas microorganisms that colonize the washing machine represent another origin of malodor, comprising a musty “wet-cloth-like” odor, which is believed to be associated with the presence of Moraxella species.15 However, Moraxella is not one of the bacteria most commonly isolated from biofilms in European washing machines2,5,17 and might be more relevant in Asia if not being able to form malodorous substances even if present in low numbers. Callewaert et al3 observed exchange of waterborne microorganisms and skin colonizers on the textile during the laundry process. It seems likely that the
formation of laundry-associated malodor is not caused by the presence of one specific species alone but that the mixture of biofilm-forming microorganisms transferred from the washing machine to the fabric and of residual contaminants from the skin remaining on the textile leads to the generation of malodor on the washed textiles. Neither the compounds that are responsible for this type of malodor nor the way these substances are formed are well understood yet. Takeuchi et al18 proposed C7-branched fatty acids to be mainly responsible for this phenomenon, which remarkably resemble molecules that are present in human sweat after bacterial metabolization. Measures against malodor generation in laundry thus include, in particular, machine care, including the use of high wash temperatures at regular intervals and thorough machine cleaning.
formation of laundry-associated malodor is not caused by the presence of one specific species alone but that the mixture of biofilm-forming microorganisms transferred from the washing machine to the fabric and of residual contaminants from the skin remaining on the textile leads to the generation of malodor on the washed textiles. Neither the compounds that are responsible for this type of malodor nor the way these substances are formed are well understood yet. Takeuchi et al18 proposed C7-branched fatty acids to be mainly responsible for this phenomenon, which remarkably resemble molecules that are present in human sweat after bacterial metabolization. Measures against malodor generation in laundry thus include, in particular, machine care, including the use of high wash temperatures at regular intervals and thorough machine cleaning.
 FIGURE 46.1 Utilization cycle of textiles showing the input and removal of microorganisms. Modified after Bockmühl.1 |
PRINCIPLES OF LAUNDRY HYGIENE—FACTORS INFLUENCING THE HYGIENE EFFICACYLaundering aims to restore the usable state of textiles by removing malodors and visible dirt and also provide a safe and sanitized textile. Whereas the term cleaning mostly refers to the removal of dirt and stains, laundry sanitization and hygiene also includes measures to (1) lower the bioburden (ie, the population of viable microorganisms on laundry items), (2) prevent cross-contamination (ie, the transfer of microorganisms from one item to the other), and (3) reduce the microbial load in the washing liquor. The reduction of the microbial load on laundry items results from the inactivation or killing of the microorganisms that are attached to the fiber as well as from the detachment and mechanical removal of the microbial cells. Because reducing the infection risk is not the only aim of laundering, especially in the domestic area, laundering can thus be understood as all means that help to make textiles fit for their dedicated purpose.
According to Sinner,19 the cleaning performance of a washing process is determined by four parameters: chemistry, temperature, time, and mechanical action. Because these factors also affect the antimicrobial performance of the process, their role in laundry hygiene is discussed here. Despite these process parameters, the quality and quantity of contamination (ie, the microbial species and the soil matrix embedding the cells as well as the amount and nature of soil) are some of the additional factors that might affect the antimicrobial efficacy of the laundering process.
Detergents and Additives
When discussing the influencing parameters in laundry according to the Sinner19 principle, the term chemistry can be understood as the action of detergents and laundry additives. Two ingredient categories particularly
determine the antimicrobial performance of detergents: surfactants and bleaching agents. Whereas the main function of surfactants in the laundering process is to provide a basic cleaning efficacy by removing hydrophobic soil, hence also supporting the detachment and the physical removal of microbial cells from the fibers, rather than the inactivation of the microorganisms,20,21 the main function of bleach in laundering is achieving a discoloration by oxidizing the chromophore groups in the stain molecules. Moreover, bleach oxidizes other organic compounds like odorous substances and reacts with microorganisms, making it the major antimicrobial component in laundry detergents. Today, the most common types of bleach are sodium hypochlorite and activated oxygen bleach (AOB). In Japan, America, Southern Europe, and other regions where traditionally cold water is used for laundering, the use of chlorine bleach is common due to its high activity at temperatures as low as 20°C (68°F), whereas oxygen-based bleach systems have prevailed in Western and Northern Europe. Most of these agents use percarbonate and a bleach activator, such as tetraacetylethylenediamine (TAED), which leads to a strong and permanent release of peracetic acid also at rather low temperatures. For domestic use, liquid and solid detergent types are available, which, apart from the way of dosage, also differ in their composition. Whereas solid heavy-duty detergents normally contain AOB, exerting a high antimicrobial efficacy in laundry washing processes, liquid detergents do not. The application of AOB in detergents was shown to significantly increase the reduction of the microbial load on textiles.22 In liquid detergents, surfactants may be considered as the only ingredient mediating the antimicrobial efficacy of a laundering process. However, although surfactants can support the detachment of the microorganisms from the surface, they do not have a microbicidal action per se. Application-oriented experiments suggest that the effect of the detergents on the reduction of microbial loads on textiles largely depends on the type of microorganism. Whereas the reduction of Staphylococcus aureus and Enterococcus hirae was strongly increased with liquid detergent compared to laundering with water alone, the reduction was not affected in case of Pseudomonas aeruginosa, Candida albicans, and Trichophyton mentagrophytes.21 It should be mentioned that special products and those used in industrial and institutional laundering may contain other oxidizing agents (eg, hydrogen peroxide or phthalimidoperoxyhexanoic acid [PAP]).
determine the antimicrobial performance of detergents: surfactants and bleaching agents. Whereas the main function of surfactants in the laundering process is to provide a basic cleaning efficacy by removing hydrophobic soil, hence also supporting the detachment and the physical removal of microbial cells from the fibers, rather than the inactivation of the microorganisms,20,21 the main function of bleach in laundering is achieving a discoloration by oxidizing the chromophore groups in the stain molecules. Moreover, bleach oxidizes other organic compounds like odorous substances and reacts with microorganisms, making it the major antimicrobial component in laundry detergents. Today, the most common types of bleach are sodium hypochlorite and activated oxygen bleach (AOB). In Japan, America, Southern Europe, and other regions where traditionally cold water is used for laundering, the use of chlorine bleach is common due to its high activity at temperatures as low as 20°C (68°F), whereas oxygen-based bleach systems have prevailed in Western and Northern Europe. Most of these agents use percarbonate and a bleach activator, such as tetraacetylethylenediamine (TAED), which leads to a strong and permanent release of peracetic acid also at rather low temperatures. For domestic use, liquid and solid detergent types are available, which, apart from the way of dosage, also differ in their composition. Whereas solid heavy-duty detergents normally contain AOB, exerting a high antimicrobial efficacy in laundry washing processes, liquid detergents do not. The application of AOB in detergents was shown to significantly increase the reduction of the microbial load on textiles.22 In liquid detergents, surfactants may be considered as the only ingredient mediating the antimicrobial efficacy of a laundering process. However, although surfactants can support the detachment of the microorganisms from the surface, they do not have a microbicidal action per se. Application-oriented experiments suggest that the effect of the detergents on the reduction of microbial loads on textiles largely depends on the type of microorganism. Whereas the reduction of Staphylococcus aureus and Enterococcus hirae was strongly increased with liquid detergent compared to laundering with water alone, the reduction was not affected in case of Pseudomonas aeruginosa, Candida albicans, and Trichophyton mentagrophytes.21 It should be mentioned that special products and those used in industrial and institutional laundering may contain other oxidizing agents (eg, hydrogen peroxide or phthalimidoperoxyhexanoic acid [PAP]).
TABLE 46.1 Microorganisms present on textiles (tex) and in the washing machine (wm) possibly originating from environment (en) or from human sources (h) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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