Influence of Sampling Site and other Environmental Factors on the Bacterial Community Composition of Domestic Washing Machines

Abstract

Modern, mainly sustainability-driven trends, such as low-temperature washing or bleach-free liquid detergents, facilitate microbial survival of the laundry processes. Favourable growth conditions like humidity, warmth and sufficient nutrients also contribute to microbial colonization of washing machines. Such colonization might lead to negatively perceived staining, corrosion of washing machine parts and surfaces, as well as machine and laundry malodour. In this study, we characterized the bacterial community of 13 domestic washing machines at four different sampling sites (detergent drawer, door seal, sump and fibres collected from the washing solution) using 16S rRNA gene pyrosequencing and statistically analysed associations with environmental and user-dependent factors. Across 50 investigated samples, the bacterial community turned out to be significantly site-dependent with the highest alpha diversity found inside the detergent drawer, followed by sump, textile fibres isolated from the washing solution, and door seal. Surprisingly, out of all other investigated factors only the monthly number of wash cycles at temperatures ≥ 60 • C showed a significant influence on the community structure. A higher number of hot wash cycles per month increased microbial diversity, especially inside the detergent drawer. Potential reasons and the hygienic relevance of this finding need to be assessed in future studies.

Cultivation-based quantification and identification of bacteria at two hygienic key sides of domestic washing machines

“…By far, micrococci and staphylococci were the most frequently isolated genera, which is in contrast to the different molecular studies mentioned here (9, 10) and might represent a cultivation bias. Micrococci and staphylococci represent ubiquitous microorganisms that are often isolated from skin and mucous membranes of humans and animals, but also from air and water.…”

“…In accordance with previous studies (7, 9, 10), Proteobacteria (29%), Actinobacteria (27%), Firmicutes (26%) and Bacteroidetes (0.5%) represented the most abundant phyla. In accordance with the relatively most abundant species found in our previous molecular study (9), Pseudomonas oleovorans , Acinetobacter parvus , and Moraxella osloensis were also detected here by cultivation in the door seal, while Rhizobium radiobacter was detected in the detergent drawer (Table 1) (9).…”

“…In addition, some of the identified species are well-known biofilm formers, such as Staphylococcus epidermidis , Micrococcus luteus , Bacillus cereus and Pseudomonas sp. (2, 4, 7, 9, 10, 19–22).…”

“…In a recent molecular study on the bacterial community of domestic washing machines, we identified the detergent drawer as the site with the highest bacterial diversity and the door seal as the site with highest relative abundance of malodor forming Moraxella osloensis species. Per site, 30-60% of the relatively most abundant sequence types were closely related to potentially pathogenic bacteria, such as Brevundimonas vesicularis or Pseudomonas aeruginosa inside the detergent drawer and Moraxella osloensis or Acinetobacter parvus inside the door seal (9). In a startling study, an antibiotic resistant Klebsiella oxytoca strain was recently isolated from biofilms of detergent drawer and door seal of a domestic washing machine used for the woollen laundry of a paediatric hospital ward, from which it probably had colonized newborns (11).…”

Site-specific molecular analysis of the bacteriota on worn spectacles

“…OTUs classified as Enhydrobacter rather seem to be affiliated with Moraxella osloensis. which is a member of the respiratory tract and nasophyryngeal microbiota that is also known to cause malodor on washed laundry 24,31,32 . The majority of the taxa displayed in Table 1 belong to risk group 2, i.e.…”