HYGIENE

ANGELINA ECKERT, YVONNE BOOTEN, MAREIKE JARCHOW, RALF LUCASSEN, LENA NEMITZ, DIRK P. BOCKMÜHL* *Corresponding author Rhine-Waal University of Applied Sciences, Marie-Curie-Str. 1, 47533 Kleve, Germany

Dirk P. Bockmuehl

Reduction of microorganisms by ironing

KEYWORDS: ironing, germ-reducing-effect, steam, laundry

The reprocessing of textiles after use has a great relevance from a hygienic point of view, because Abstractclothes can be potential vectors for the transmission of infectious diseases. Although ironing is used regularly for treating garments after laundry, little is known about its germ-reducing effect. To constitute a realistic situation of ironing in a laboratory experiment, textile germ carriers were contaminated with representative microorganisms prior to ironing under a larger and thicker piece of cloth by using different temperatures with and without steam. By this process it should be determined whether the cloth reaches a suffi cient internal temperature to effi ciently reduce microorganisms.

INTRODUCTION MATERIALS & METHODS

While the treatment of potentially contaminated laundry Overnight cultures of the examined microorganisms were grown in many public areas, such as hospitals are carried out in CASO-broth (Oxoid, Wesel, Germany) (for Escherichia coli according to specifi ed processes and special methods, (DSM 682) and Staphylococcus aureus (DSM 799) or Malt-broth there are no standardized conditions for this treatment in (Oxoid, Wesel, Germany) for Candida albicans (DSM 1386). the domestic area (1). To lower a potential infection risk, all Germ carriers were prepared by immersing cotton pieces (2x2 treatment steps of the textiles must be considered. However, cm) in the culture vessels followed by drying for 30 minutes at the aspect of the germ reduction on the textiles by ironing 37°C. The dryed carriers were placed under a thicker cotton is most largely unexplored. A study of Reploh showed that cloth (wfk 10A, wfk, Testgewebe GmbH, Brüggen, Germany) ironing represents a supplementary measure for the germ and ironed with an electric iron (Rowenta DZ 5020) for domestic reduction after the washing process, but no signifi cant germ purposes according the following scheme (Figure 1): reduction could be detected after the normal ironing process (2). In another study Blümke et al. could show that the microbial contamination of the laundry is higher after the washing process in a washing machine than before. The results support the idea that garments and towels can be potential germ carriers (3). A thermal treatment after washing could represent one opportunity to reduce the number of bacteria on the textiles under these circumstances. The primary purpose of ironing is smoothing the textiles, with temperature, duration and hot steam being important parameters for an optimal ironing result. Because the textiles might be damaged when too high temperatures are applied, the ironing recommendations for the used textiles were Figure 1. Schematic overview of the applied times and temperatures when ironing. Temperature 1 and 2 correspond to a iron-setting of 1 or 3 points, respectively respected to achieve realistic results.

34 H&PC Today - Household and Personal Care Today, Vol. 9 nr. 4 July/August 2014 The germ carriers were ironed without steam at 75°C and The initial cell count was adjusted to 105 for E. coli and S. 120°C for 3 and 9 seconds each, while ironing with steam aureus and to 106 for C. albicans. A germ reduction after was possible only for the highest temperature of 120°C. The ironing can be seen for all three microorganisms. While E. latter germ carriers were also ironed for 3 and 9 seconds. coli was inactivated at high temperature conditions even The temperature of the iron was measured by means of an without steam, a complete inactivation for S. aureus could infrared Thermometer (Pioneer EM-A350). The ironing time of only be obtained when additional steam was applied at 3 seconds corresponded to an average ironing time normally high temperature. The temperature-sensitivity of S. aureus used in the domestic settng. The ironing time of 9 seconds at can be observed at 120°C and 9 seconds, where a reduction a temperature of 120°C was chosen to evaluate the maximal by almost 103 cfu per carrier was observed. C. albicans germ reduction effect still related to achievable parameters was not completely inactivated under the test conditions. in the domestic setting. One germ carrier of each tested Interestingly, when using low temperature conditions or microorganism was handled accordingly but without prior even high temperature with short contact times, virtually no ironing to determine the initial cell count. For the negative inactivation of S. aureus and C. albicans was observed. controls germ carriers were ironed, without and with the test microorganisms. For the determination of the starting cell count of the microbial suspensions, serial dilutions up to 10-8 DISCUSSION & OUTLOOK were made and 100 µl of each dilution was plated on CASO- agar-plates (Oxoid, Wesel, Germany). After incubation for 24 Although ironing must be considered as a common practice hours at 37°C, the colony forming units were counted. within the treatment of textiles, studies on the antimicrobial Directly after ironing the precise temperature was determined effects of ironing are almost completely lacking . Back on the surface of the germ carriers using an infrared in the 1960s, Reploh came to the conclusion that ironing thermometer. The germ carriers were then shaken in 10 ml might contribute to the hygienic processing of textiles of the appropriate medium in an Erlenmeyer flask for 15 min. but must be considered insufficient by itself (2). This study at 450 rpm to remove all remaining microbial cells and were attempted to mimick conditions more realistic of those in the analyzed by a 6-step MPN method. All experiments were domestic environment for the ironing of textiles, although performed in triplicate. the amount of bacterial cells applied to the germ carriers must be considered quite high with regards to “normal” contamination levels, especially on freshly laundered textiles RESULTS (3). Nevertheless, the findings that ironing might not be an efficient means for the decontamination of textiles could be Figure 2 shows the average number of remaining microbial confirmed in general, although the use of steam and high cells on three germ carriers after ironing. temperature conditions when ironing might contribute to the inactivation of microbial cells remaining on garments after laundering. However, the high tolerance of fungi like C. albicans to ironing suggest for a safe elimination during the prior laundry process by using high washing temperatures and bleach-containing detergents (4). Although the distinct temperature-sensitivity of different microbial species must be considered, ironing seems to be an appropriate means to further reduce Gram-negative bacteria in particular. Especially when kitchen-textiles are considered, that might be contaminated with gram-negative bacteria, such as Salmonella or Campylobacter, ironing might (at least partly) compensate for an insufficient germ reduction due to lower washing temperatures and the use of bleach- free detergent. Nevertheless, Temperature and the use of activated oxygen bleach or similar approaches must still be considered inevitable to achieve a “good” hygiene standard via laundering.

REFERENCES AND NOTES Figure 2. Logarithmic reduction of microorganisms by ironing. The remaining cell counts after ironing are shown with respect to the initial cell count before ironing. Columns represent the mean 1. Bloomfield, Exner, Signorelli, Jyoti Nath and Scott (2011) The infec- value of three independent experiments; error bars indicate the tion risks associated with clothing and household linens in home standard error of the mean. and everyday life settings, and the role of laundry. International Scientific Forum on Home Hygiene (IFH) 2. Reploh et al. (1965) Untersuchungen über die Keimabtötung beim Bügeln und Dämpfen der Kleidung. Arch Hyg Bakteriol. 149(7):610 The results are represented with ascending ironing 3. Blümke et al. (2011) The washing machine as a major source for temperature in figure 2 from left to right. The low microbial contaminations of domestic laundry. 7th European temperature condition (1 point) corresponded to a Detergents Conference; Fulda, October 2011 measured temperature of approximately 75°C. The high 4. Hammer et al. (2011) Infection risk by dermatophytes during stor- temperature conditions (3 points) corresponded to a age and after domestic laundry and their temperature-depen- temperature of approximately 120°C. dent inactivation. Mycopathologia 171(1):43

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