The washing machine as a source of microbial contamination of domestic laundry – a case study
During recent years efforts to save energy led to the use of lower washing temperatures (< 60 °C) although it is widely accepted that laundry procedures using liquid detergents without activated oxygen bleach (AOB) at low temperatures may cause hygiene problems. Furthermore there is growing evidence that the washing machine itself may serve as a vector in the contamination of textiles. In this case study we investigated the role of the washing machine in terms of distribution of microorganisms to textiles. We analyzed 37 naturally contaminated sample towels (each used for five consecutive days) with respect to their microbial contamination after use, after washing in a standard household washing machine with liquid detergent at 30°C and after air-drying. The sample towels exhibited a total viable count of 100 – 103 cfu/cm2 after use, while after laundering the microbial load increased to 101- 104cfu/cm2 (mean difference = 2.3 x 103 cfu/cm2; p= 0.009). When investigating unused control towels in the experiments the intrinsic contamination caused by the washing machine was found at 101-102 cfu/cm2 (mean difference = 1.4 x 102 cfu/cm2; p= 0.050). Although microbial counts after air-drying decreased to values similar to that of used towels before laundry, the results suggest a role of the household washing machine in the contamination of textiles during laundering at low temperature.
During recent years efforts to save energy led to the use of lower washing temperatures (< 60 °C) although it is widely accepted that laundry procedures using liquid detergents without activated oxygen bleach (AOB) at low temperatures may cause hygiene problems. Amongst others Lichtenberg et al. (1) investigated the effect of low washing temperatures in terms of the reduction of microbial contaminations (Enterococcus faecium and Staphylococcus aureus) of textiles when detergents with or without AOB were used. In that study, detergent powder with AOB led to a reduction > 3 log even at washing temperatures of 30 °C. When liquid detergent (without AOB) was used a log reduction of > 3 was only achieved when laundering was performed at 60°C. At 30°C and 40°C the log reduction decreases to 2.3-2.4. We found comparable result in a previous study with towels contaminated by normal use (2), where regardless of the detergent, washing temperatures above 60°C led to complete reduction of microorganisms. However at 40°C the detergent without AOB showed only partial reduction of microbes and at 30°C detergents with and without AOB exhibit ...