The washing machine as a reservoir for transmission of extended spectrum beta-lactamase (CTX-M-15)-producing Klebsiella oxytoca ST201 in newborns

During the time period from April 2012 to May 2013, 13 newborns (1 - 4 weeks old) and one child in a paediatric hospital ward in Germany were colonized with an extended spectrum betalactamase (ESBL) producing Klebsiella oxytoca (CTX-M-15). A microbiological source-tracking analysis, including human and environmental samples, was carried out to identify the source and transmission pathways of the K. oxytoca clone. In addition, different hygienic intervention methods were evaluated. Isolates of the K. oxytoca strains were detected in the detergent drawer and on the rubber door seal of a domestic washer-extractor machine, used in the same ward to wash laundry of the newborns as well as in two sinks. These strains were typed using PFGE and multi-locus sequence typing (MLST). The environmental findings were compared with those of the human strains and the isolates detected on the clothing. The results showed that the strains were identical using both techniques, (ST201 and pulse-field-gel-electrophoresis [PFGE] type-00531, a clone specific to this hospital and not previously isolated in Germany), emphasizing the washing machine as a reservoir and fomite for the transmission of these multidrug-resistant bacteria (MDR). After the washing machine had been taken out of use, no further colonizations were detected over a following 4-year period. Importance Washing machines should be further investigated as possible sites for horizontal gene transfer (ESBL-genes) and cross-contamination of clinically important Gram-negative strains. Particularly in the healthcare sector, the knowledge of possible (re-) contamination of laundry (patients9 clothes, staff uniforms) with multidrug-resistant Gram-negative bacteria could help to prevent and control nosocomial infections. This report describes an outbreak with a single strain of a multidrug-resistant bacterium (Klebsiella oxytoca ST201) in a neonatal intensive care unit, that was only terminated when the washing machine was removed. In addition, the study implies that changes in washing machine design and processing are required to prevent accumulation of residual water where microbial growth can occur and contaminate clothes.