Microbial Diversity and Putative Opportunistic Pathogens in Dishwasher Biofilm Communities

Abstract

Extreme habitats are not only limited to natural environments, but also exist in manmade systems, for instance, household appliances such as dishwashers. Limiting factors, such as high temperatures, high and low pHs, high NaCl concentrations, presence of detergents, and shear force from water during washing cycles, define microbial survival in this extreme system. Fungal and bacterial diversity in biofilms isolated from rubber seals of 24 different household dishwashers was investigated using next-generation sequencing. Bacterial genera such as Pseudomonas, Escherichia, and Acinetobacter, known to include opportunistic pathogens, were represented in most samples. The most frequently encountered fungal genera in these samples belonged to Candida, Cryptococcus, and Rhodotorula, also known to include opportunistic pathogenic representatives. This study showed how specific conditions of the dishwashers impact the abundance of microbial groups and investigated the interkingdom and intrakingdom interactions that shape these biofilms. The age, usage frequency, and hardness of incoming tap water of dishwashers had significant impact on bacterial and fungal community compositions. Representatives of Candida spp. were found at the highest prevalence (100%) in all dishwashers and are assumed to be one of the first colonizers in recently purchased dishwashers. Pairwise correlations in tested microbiomes showed that certain bacterial groups cooccur, as did the fungal groups. In mixed bacterial-fungal biofilms, early adhesion, contact, and interactions were vital in the process of biofilm formation, where mixed complexes of bacteria and fungi could provide a preliminary biogenic structure for the establishment of these biofilms.IMPORTANCE Worldwide demand for household appliances, such as dishwashers and washing machines, is increasing, as is the number of immunocompromised individuals. The harsh conditions in household dishwashers should prevent the growth of most microorganisms. However, our research shows that persisting polyextremotolerant groups of microorganisms in household appliances are well established under these unfavorable conditions and supported by the biofilm mode of growth. The significance of our research is in identifying the microbial composition of biofilms formed on dishwasher rubber seals, how diverse abiotic conditions affect microbiota, and which key microbial members were represented in early colonization and contamination of dishwashers, as these appliances can present a source of domestic cross-contamination that leads to broader medical impacts.

Rumen Virus Populations: Technological Advances Enhancing Current Understanding

“…Biofilms are ubiquitous in nature and most bacteria as well as a number of fungal and yeast species, have the potential to form a biofilm. The biofilms that develop are often poly-microbial and inter-kingdom communities (Swidsinski et al, 2013;Smith et al, 2016;Raghupathi et al, 2018).…”

High Incidence of an Emerging Opportunistic PathogenCandida parapsilosisin Water-Related Domestic Environments

“…Raw natural water, contaminated with C. parapsilosis, included streams [2], rivers [3], and groundwater [4]. Its presence positively correlated with the occurrence of dry season [3], the presence of middle-hard water type and nitrates [4,18,20]. Due to its ability to withstand filtration and chlorination process [21], C. parapsilosis is one of the building blocks in biofilms within municipal water systems, with the number of yeast cells in a range of 3.1-4.6 CFU/cm 2 [22].…”

“…Recent studies have shown that under these unfavourable conditions, such as high temperature, wet and dry periods, high and low pH, presence of high concentrations of salt (NaCl) and water shearing forces, a certain group of microorganisms-polyextremotolerant ones-are enriched [34]. These unfavourable circumstances can defy also the opportunistic pathogenic species like C. parapsilosis [17], which seems to be one of the first colonisers of new dishwashers [20], providing a biotic surface for the construction of mixed bacterial-fungal biofilms [35]. C. parapsilosis forms together with Exophiala dermatitidis, Exophiala phaeomuriformis, Rhodotorula mucilaginosa, Aureobasidium melanogenum, Bisifusarium dimerum (formerly Fusarium dimerum), Fusarium oxysporum and Saprochaete clavata, a stable microbiota of dishwasher rubber seals worldwide [17,34,36,37].…”

“…Drains, cutlery racks and side nozzles are less exposed [17]. Higher dishwasher frequency of use (7-14 times per week) and connection to tap water system with moderately hard tap water hardness (1.5-2 mmol/l CaCO 3 ) significantly affect the incidence of C. parapsilosis [20]. C. parapsilosis can be released from dishwashers via waste water, cleaned vessels and hot aerosols, formed at the end of the washing cycle [17].…”

“…Survival of microorganisms invading household niches is higher due to biofilm formation [17]. Next-generation sequencing of dishwasher biofilm community and further usage of several statistical models showed that Candida (C. parapsilosis) is one of the first colonisers of rubber seals in dishwashers [20].…”