The bacterium involved was a single clone of Klebsiella oxytoca. The study showed how the organisms were transmitted repeatedly to new babies in a ward located in a children’s hospital. The transmission of the organism halted only when a ‘smoking gun’ washing machine was disassembled and removed from the hospital.
Microbiologists, as reported by the American Society for Microbiology, have demonstrated how resistance genes, as well as many water-borne microorganisms, can persist in domestic washing machines at reduced temperatures.
Klebsiella oxytoca is a Gram-negative, rod-shaped bacterium that is closely related to K. pneumoniae. Outbreaks of antibiotic-resistant Klebsiella oxytoca have occurred in multiple hospitals and ICUs throughout the world.
With the hospital case study, standard screening protocols demonstrated the presence of the Klebsiella organism on infants in the ICU. Genetic comparative testing traced the source of the bacterium to the washing machine. In the course of the investigation, both incubators (used for babies born prematurely) and healthcare workers were ruled out as the sources of the contamination.
It appears that clothes, like knitted caps and socks, and blankets washed in the machine transmitted K. oxytoca from the washer to the infants. The residual water on the rubber mantle of the washer together with the final rinsing process (where unheated water is used) were found to contain the contaminant.
The infants in the intensive care units (ICU) were colonized, but not infected by K. oxytoca. However, the potential for a serious public health risk exists unless action is taken.
Lead researcher Dr. Martin Exner states: “We have proven for the first time that a washing machine can also spread antibiotic-resistant bacteria to humans.”
The research also carries implications for household washers, as well as those located in hospitals. This may relate to factors associated with energy management and environmental concerns. The water temperatures used in many domestic washing machines have been declining, ostensibly to save energy (and money). This was driven temperatures to regularly to be below 60°C (140°F). At such temperatures the water is less effective in terms of killing vegetative bacteria.
The study recommended that changes in washing machine design and processing are needed in order to prevent the accumulation of residual water leading to conditions favorable for microbial growth.
The case study has been reported to the journal Applied and Environmental Microbiology, with the research paper headed “The washing machine as a reservoir for transmission of extended spectrum beta-lactamase (CTX-M-15)-producing Klebsiella oxytoca ST201 in newborns.”
