The dishwasher rubber seal acts as a reservoir of bacteria in the home environment

Abstract

Bacteria that colonise the extreme environment of household dishwasher rubber seals were investigated using cultivation-dependent and metagenomic approaches. All 30 dishwashers investigated were colonised by various bacteria. Cultivation approaches resulted in 632 bacterial isolates in total, belonging to four phyla, eight classes, 40 genera and 74 species. The majority were Gram-positive, as solely Firmicutes (dominated by the Bacillus cereus group) and Actinobacteria. Gammaproteobacteria were primarily represented by Stenotrophomonas maltophilia, Pseudomonas aeruginosa and Escherichia coli. All isolates were tested for resistance to seven selected antibiotics. Metagenomic assessment of the bacterial biodiversity of the dishwasher rubber seals confirmed the predominance of Gram-positive bacteria, as primarily Actinobacteria, followed by Proteobacteria dominated by Gammaproteobacteria, and by pathogenic species such as Escherichia sp., Acinetobacter baumannii, Pseudomonas sp., Stenotrophomonas maltophilia, and Enterobacter sp.. Metagenomic assessment of bacterial biodiversity in the tap water connected to dishwashers revealed predominance of Gram-negative bacteria, in particular Proteobacteria, mainly represented by Tepidimonas sp.. Both Actinobacteria and Firmicutes showed low numbers in the tap water. These data indicate that colonisation of dishwasher rubber seals probably depends primarily on the bacterial input from the dirty vessels, and much less on the bacteria in the tap water. Based on the antibiotic resistance data, the dishwasher rubber seal bacterial isolates do not represent a serious threat for the spread of antibiotic resistance into the household environment. Nevertheless dishwashers cannot be ignored as potential sources of human infections, in particular for immuno-compromised individuals.

The household resistome – frequency of beta-lactamases, class 1 integron and antibiotic resistant bacteria in the domestic environment

“…In dishwashers, no bacterial growth was detected after test runs except for the eco-program, thus cleaned dishes seem to be no source of the tested strains. However, ABR bacteria were isolated from rubber door seals and DW sieves and have already been identified as a source of pathogenic and opportunistic pathogenic bacteria and fungi (42,63,64). Zupančič et al (2019) determined a low phenotypic ABR potential in DW, which is confirmed by our study since less resistant strains were isolated compared to SD and WM.…”

“…Previous studies revealed the presence of bla genes (26) and the correlation of multiresistance with intI1 (16) in the domestic environment, but no studies on the frequency distribution of bla genes and their co-occurrence in private households, especially in relation to phenotypic resistance, have been conducted so far. SD, WM and DW provide a good habitat for microbial communities with a steady nutrient supply in a humid environment, promoting bacterial growth and biofilm formation (39)(40)(41)(42). Besides, ABR bacteria and antibiotic residues have been detected in siphons of hospitals (43,44), indicating their occurrence in SD of domestic areas as well.…”

The Household Resistome: Frequency of β-Lactamases, Class 1 Integrons, and Antibiotic-Resistant Bacteria in the Domestic Environment and Their Reduction during Automated Dishwashing and Laundering

“…Previous studies revealed the presence of bla genes ( 32 ) and the correlation of multiresistance with intI1 ( 15 ) in the domestic environment, but no studies on the quantitative prevalence of bla genes and their co-occurrence in private households, especially in relation to phenotypic resistance, have been conducted so far. SD, WM, and DW provide good habitats for microbial communities with a steady nutrient supply in a humid environment, promoting bacterial growth and biofilm formation ( 39 , 47 – 49 ).…”

“…No bacterial growth was detected in dishwashers after test runs, except with the ecoprogram; thus, cleaned dishes do not seem to be a source of the tested strains. However, antibiotic-resistant bacteria were isolated from rubber door seals and DW sieves and have already been identified to be a source of pathogenic and opportunistic pathogenic bacteria and fungi ( 40 , 49 , 74 ). Zupančič et al ( 49 ) determined a low phenotypic ABR potential for strains from DW, a finding which was confirmed by our study, since fewer resistant strains were isolated from DW than from SD and WM.…”

“…However, antibiotic-resistant bacteria were isolated from rubber door seals and DW sieves and have already been identified to be a source of pathogenic and opportunistic pathogenic bacteria and fungi ( 40 , 49 , 74 ). Zupančič et al ( 49 ) determined a low phenotypic ABR potential for strains from DW, a finding which was confirmed by our study, since fewer resistant strains were isolated from DW than from SD and WM. Nevertheless, DW samples revealed a high absolute abundance of ARGs, and the strains that were isolated still harbored bla genes and thus can be considered a potential source of antibiotic-resistant bacteria as well.…”