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.