Cultivation-Based Quantification and Identification of Bacteria at Two Hygienic Key Sides of Domestic Washing Machines.

Susanne Jacksch,Huzefa Zohra,Mirko Weide,Markus Egert,Sylvia Schnell

doi:10.3390/microorganisms9050905

Susanne Jacksch, Huzefa Zohra + Show 3 more

Open Access

https://doi.org/10.3390/microorganisms9050905

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Abstract

Detergent drawer and door seal represent important sites for microbial life in domestic washing machines. Interestingly, quantitative data on the microbial contamination of these sites is scarce. Here, 10 domestic washing machines were swab-sampled for subsequent bacterial cultivation at four different sampling sites: detergent drawer and detergent drawer chamber, as well as the top and bottom part of the rubber door seal. The average bacterial load over all washing machines and sites was 2.1 ± 1.0 × 104 CFU cm−2 (average number of colony forming units ± standard error of the mean (SEM)). The top part of the door seal showed the lowest contamination (11.1 ± 9.2 × 101 CFU cm−2), probably due to less humidity. Out of 212 isolates, 178 (84%) were identified on the genus level, and 118 (56%) on the species level using matrix-assisted laser desorption/ionization (MALDI) Biotyping, resulting in 29 genera and 40 identified species across all machines. The predominant bacterial genera were Staphylococcus and Micrococcus, which were found at all sites. 22 out of 40 species were classified as opportunistic pathogens, emphasizing the need for regular cleaning of the investigated sites.

Highlights

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
The sampling site with the lowest cell numbers was the top part of the rubber door seal (RDST, 11.1 ± 9.2 × 101 colony-forming units (CFU) cm−2 ), probably because water quickly drains off from here
Despite its small sample size, our study clearly shows that both the detergent drawers and bottom door seals of domestic washing machines are significantly contaminated with cultivable bacteria, including significant shares of potentially pathogenic ones

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Representing wet, warm, and nutrient-rich environments, many sites of domestic washing machines offer ideal living conditions for microorganisms, such as bacteria and fungi [1,2]. Microbial contamination of washing machines might cause unaesthetic staining as well as malodor formation [3,4]. Microbial biofilms might serve as reservoirs for (potentially) pathogenic microorganisms that might contaminate the laundry and thereby pose a health threat for susceptible persons [5,6]

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