Factors affecting the bacteriological contamination of commercial washing machines

Wash water from self-service washing machines in three commercial launderettes of Bologna (Italy) were examined to verify which factors affect their bacterial contamination and to determine which procedures in the laundering process have the most significant effects on the removal of bacteria. Four washing formulas were compared: a delicates cycle (programmed temperature 25-30 degrees C; actual temperature: 28-31 degrees C); a whites cycle (programmed temperature: 80-90 degrees C; actual temperature: 50-57.5 degrees C); a delicates cycle with the addition of an oxygen-based bleach safe for delicate fabrics and a whites cycle with the addition of an oxygen-based bleach. Bacterial contamination of washing machines was higher in the launderette most heavely used, and, furthermore, it was in relation with the washing temperature and the use of bleaches. The low temperature laundering cycle (20-30 degrees C) did not guarantee elimination of bacterial content from either the inside of the washing machine or from the fabric being washed. Washing with water at a higher temperature, of about 55 degrees C, or adding an oxygen-based bleach to the low temperature cycle did ensure a significant reduction in bacterial recovery from water samples and fabrics, but did not prevent bacteria such as P. aeruginosa from surviving inside the washing machine. Only the addition of bleaches to the hot water program ensured the almost total elimination of bacteria and also guaranteed their elimination from protected parts of the drum.