Reduction of Methicillin-Resistant Staphylococcus aureus in fabrics using machine washing treatments and microwaves

Date

2018-08

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Abstract

The spread of methicillin-resistant Staphylococcus aureus (MRSA) infections in healthcare and community settings as well as the emergence of antibiotic-resistant pathogens in food-producing animals, farms, or meat production has created a great concern not only in public health but also in food safety. Direct physical or indirect contact with clothing, towels, and other fibrous materials is one possible route of infection or contamination with MRSA. These studies were conducted to determine the survival of MRSA in terry cotton fabrics laundered in a high efficiency washing machine using different temperature-washing cycles and after treatment with microwaves during drying. In the first study, four white towel swatches (1000 cm2) pre-inoculated with a three-strain MRSA inoculum (107 CFU/mL) and three blue, non-inoculated swatches were machine-washed using one of the following temperatures and wash cycles: (a) hot water, casual; (b) warm water, cotton; (c) cold water, delicate; and (d) hot water, cotton with chlorine bleach (1000 ppm). Control swatches only received MRSA inoculation without washing. Water samples, 50 mL each, were collected after the wash cycle and final rinse. All the samples were further cut into 100 cm2 swatches. Viable MRSA cells were enumerated by spread plate method on mannitol salt phenol-red agar (MSA) with methicillin after incubation at 37°C for 48 hours. Data from three replications were statistically analyzed by means of one-way ANOVA. Washing with detergent alone was found to be ineffective in the removal or inactivation of MRSA as significant microbial concentrations (2.83 – 4.61 Log10 CFU/cm²) were still found in the pre-inoculated swatches. In addition, substantial transfer of microorganisms from pre-inoculated swatches to sterile samples occurred during laundering. The use of bleach and high washing temperature eliminated MRSA in towels and wash water samples, and prevented cross-contamination.
The second study was performed to determine the efficacy of targeted directional microwaves (TDM) during drying to reduce MRSA in terry cloths. Towel swatches (100 cm2) were inoculated with a three-strain MRSA inoculum at 106 CFU/mL and allowed to dry for 3 hours to slight dampness. Control swatches were inoculated but not further treated. In duplicates, inoculated swatches were subjected to the following treatments: a) tumble heat dried for 20 min; b) TDM (40, 60, 80, or 120 sec) and air tumbled the remaining 20 min; or c) TDM (40, 60, 80, or 120 sec) and heat tumbled for 20 min. After treatment, viable MRSA cells were enumerated by spread plate method on mannitol salt phenol-red agar (MSA) with methicillin and tryptic soy agar (TSA) overlay after incubation at 37°C for 48 hours. Data from five replications were statistically analyzed by means of one-way ANOVA. Results indicated that the heat drying cycle of clothes drier was not a sufficient method to kill MRSA unless TDM was applied. By treating contaminated towels with TDM for more than 40 seconds in combination with heat drying and 120 second TDM only, significant reductions of ≥ 3.7 Log10 CFU/cm² were achieved.

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Keywords

MRSA in fabrics, MRSA in laundry, Microwave-dryer

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