A study of 29 washing machines and 24 dishwashers showed that genes encoding for resistance to β-lactamase antibiotics were present in 79% of the washing machines and 96% of dishwashers.
To test the impact of laundering on resistant bacteria, cotton test swatches were contaminated with antibiotic susceptible and resistant strains of Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus and laundered in a domestic washing machine with or without activated oxygen bleach (AOB)-containing detergent at 20-50°C. Bacterial reduction after laundering was ≥80% for all Ps. aeruginosa and Kl. pneumoniae strains, but only 37-61% for methicillin-resistant Staph. aureus. In general, the reduction was higher for susceptible than for resistant strains, especially for Staph. aureus.
The authors concluded that this presence of β-lactamase genes in domestic appliances may pose a potential risk for cross-contamination and transfer of genes encoding resistance against clinically important antibioitcs .
The results indicate the importance of using laundry cycles which are sufficient to prevent onward transmission of bacteria. laundry cycles should take account of the fact that the hygiene efficacy of laundering may be lower against antibiotic resistant strains, particularly Staph aureus strains. In general, higher temperatures and the use of AOB can improve the reduction of antibiotic-resistant bacteria
Laura Rehberg, André Frontzek, Åsa Melhus, Dirk P. Bockmühl,Prevalence of β-lactamase genes in domestic washing machines and dishwashers and the impact of laundering processes on antibiotic resistant bacteria. Journal of Applied Microbiology (2017) DOI: 10.1111/jam.13574
