Non-pest arthropods are a potential reservoir of human pathogens
Most studies of indoor environments have focused on pest arthropods, neglecting non-pest species and leading to an underestimation of the potential impact of non-pest arthropods as carriers of human pathogens (Bertone et al. 2016). Here, we characterized the indoor insect community and the associated microbiota over a period of 12-month across 20 households. This approach enabled us to characterize for the first time the microbiota of the arthropod indoor community and to identify potential carriers of human pathogens.
The most abundant arthropod family in the indoor environments studied here were cellar spiders of the family Pholcidae, consistent with previous findings in indoor environments (Desales-Lara et al.2013; Durán-Barrón et al. 2009; Rodríguez-Rodríguez et al.2015). Cellar spiders, together with ladybirds and cockroaches are typically found in indoor environments (Brown et al. 2008; Wanget al. 2011). However, the other arthropods found in our study were unexpected as they are outdoor species (e.g. wasps and crane flies) (Hall & Gerhardt 2002; Reed & Landolt 2019). They were likely casual intruders attracted by food and/or light (e.g., non-biting midges and spiders). These species are potential carriers of human pathogens, as their microbiota composition showed.
Our survey of the microbiota associated with non-pest arthropods identified opportunistic pathogens of humans present either in the endogenous or exogenous microbial community or both. Among the bacterial families intersecting with the HSE database, Rickettsiaceae were ubiquitous to the endogenous and exogenous microbiota of all indoor arthropods actively captured in this study. Rickettsia is a genus of Gram-negative obligate intracellular bacteria typically associated with ticks, leeches, amoeba, ciliate, and hydra (Krawczak et al.2018). They can cause typhus and spotted fever, with potential life-changing illness (Ogata et al. 2006). Bacillaceaewere the second most abundant bacteria family across the insect captures, which is responsible for foodborne infections in humans (Stenfors Arnesen et al. 2008). The genus Clostridiaceaewas also common across the insect captures; it comprises several spore-producing bacteria that can cause foodborne and other opportunistic infections (e.g., gas-gangrene) (Kierzkowska et al.2018). In addition, Corynebacteriaceae and Enterococcaceaewere found in relatively high abundance in the insects’ microbiota. The family Corynebacteriaceae includes species of the genusCorynebacterium that cause opportunistic infections in humans, such as diphtheria, endocarditis, and lymphadenitis (Zhi et al.2017) . Enterobacteriaceae are the agents of many community - and hospital-acquired infections (Perez 2018) , including urinary tract infections, surgical wounds infections and bacteraemia (Lebretonet al. 2014). Also found in the insect microbiota wereNeisseriaceae . These bacteria can be a part of the normal human bacteria flora and are typically harmless. However, some species of this family can cause infections in humans (Osses et al. 2017); for example, Neisseria gonorrhoeae and Neisseria meningitidiscause the sexually transmitted disease gonorrhoea and meningitis, respectively (Christodoulides et al. 2021).
Less abundant bacterial families in the insect captures includedPeptostreptococcaceae , commonly found in the gut of humans and animals (Neumann et al. 2020); the opportunistic bacteria familyPseudomonadaceae associated with antibacterial resistance (Saati-Santamaria et al. 2021; Wessels et al. 2021); andStaphylococcaceae . The latter are common human commensals and typically harmless. However, they can cause infections in immunocompromised people (Rossi et al. 2020).Streptococcaceae are associated with infective endocarditis, purulent infections, brain haemorrhage, intestinal inflammation and bacteraemia (Yumoto et al. 2019). The identification of human pathogens that can cause opportunistic infections in the indoor environment does not directly translate into a public health concern. However, our findings invite a closer investigation of the microbiota of non-pest arthropods as a potential reservoir of opportunistic bacteria that can cause pathogenic effects in humans. With regular screening of household environments, opportunistic infections may be prevented.