Introduction
As common organisms in indoor environments, arthropods are recognised
mechanical and biological vectors of infections in animals, including
humans (Doron & Gorbach 2008). Arthropod pests are mechanical carriers
of human pathogens, especially of gastrointestinal and other
opportunistic pathogens, including Escherichia ,Salmonella , Shigella and Campylobacter (Adamset al. 2015; Gibbons 2016). Klebsiella pneumoniaeand Staphylococcus aureus have been found to be common in the
microbiome of cockroaches collected in hospitals, whereas the same
arthropod species carries more frequently Escherichia coli,
Citrobacter spp., Pseudomonas aeruginosa andStaphylococcus spp. in domestic households (Memona et al.2017; Menasria et al. 2015; Moges et al. 2016). Flies are
also known carriers of opportunistic bacteria, such as Klebsiella
pneumoniae (Ranjbar et al. 2016), Staphylococcus and
Enterobacteriaceae (Barreiro et al. 2013).
Gastrointestinal pathogens carried by flies and cockroaches can cause
2.4 million infections and 180 deaths per year in the UK (Hollandet al. 2020) . Worldwide, pest arthropods are one of the main
factors involved in the epidemiology of diarrhoea (Rahmadani & Lee
2020), responsible for the yearly death of 525,000 children under the
age of five (Das et al. 2018). Pest arthropods play such an
important role in opportunistic infections that the control of e.g. fly
populations can reduce the incidence of gastrointestinal bacterial
infections by 23% (Das et al. 2018; Knight et al. 1992;
Sengupta et al. 1995). However, arthropod pests comprise a
minority of the indoor arthropod environment (Barberan et al.2015; Bertone et al. 2016; Leong et al. 2017); studies
start to emerge describing the abundance and diversity of non-pest
arthropods in these environments (Adams et al. 2015; Barberanet al. 2015; Bertone et al. 2016; Leong et al.2017). The role of these species as potential carriers of opportunistic
infections is, to date, understudied. However, human pathogenic bacteria
have been isolated from the microbiome of non-pest arthropods, including
dark-winged fungus gnats (Diptera: Sciaridae ) (Kwon et al.2016); owl midges (Diptera: Psychodidae ) (Faulde & Spiesberger
2013) , and cellar spiders (Araneae: Pholcidae) (Voloshyn et al.2017). In addition, studies on household surfaces have shown the
presence of both human-associated pathogens, includingStaphylococcus , Streptococcus, Corynebacterium ,Lactococcus and Enterobacteriaceae , as well as bacteria
associated with the outdoor environment, such as Pseudomonas ,Propionibacterium , Streptophyta and Sphingomonas(Jeon et al. 2013). However, a systematic characterization of
non-pest arthropods diversity and their associated microbiota as
potential carriers of human pathogens in indoor environments is lacking.
Moreover, the screening of pathogenic bacteria associated with
arthropods is conducted prevalently with culture-based approaches.
Culturable bacteria only constitute 2.5% of existing bacteria, severely
limiting the characterization of bacterial communities associated with
the indoor environment (Oberauner et al. 2013) .
Here, we study the indoor arthropod community and its associated
microbiota, sampled from twenty households located in the West Midlands
(UK). The households were evenly split between urban and suburban
environments and sampling was conducted by citizen scientists through
active captures over a period of 12 months. We classified the arthropods
and their relative abundance across the 12-month sampling period using
taxonomic cues against entomological references. We applied DNA
metabarcoding and culture-based approaches to study the composition and
relative abundance of endogenous (gut) and exogenous (exoskeleton)
microbiota of the captured arthropod morphospecies. We determined
whether the microbiota dynamics and composition were explained by the
association with the arthropod morphospecies, the sampling environment
(urban/suburban) and the season (month of collection). We then
determined how many bacteria families identified in the arthropod
microbiota were recognized as human pathogens according to the list of
biological agents by the Advisory Committee on Dangerous Pathogens
(HSE). Our study provides important insights into the role of non-pest
arthropods as potential carriers of opportunistic pathogens for animals
and humans, with implications for public health.