Cold storage, hot spots: Household refrigerators as under-recognized hubs of microbial diversity

Abstract

Household refrigerators are indispensable for food storage but also serve as reservoirs for diverse microbial communities, including potential pathogens. International guidelines recommend storage below 5 °C but give little guidance on domestic refrigerator hygiene. This study investigates how temperature and hygiene shape microbial burden, antimicrobial resistance, and community structure in domestic refrigerators using shotgun metagenomic sequencing at species-level resolution. Swabs from 45 refrigerators revealed substantial diversity, with Acinetobacter, Pseudomonas, and Staphylococcus as dominant genera. Only 38% of refrigerators maintained temperatures below 5 °C, while 24% exceeded 7 °C. Cleaning frequency was the key factor associated with bacterial cell equivalents (BCE) and diversity, with high loads linked to infrequent cleaning. Pathogenic species, including Bacillus cereus and Staphylococcus aureus, were detected in 60% of refrigerators; Listeria monocytogenes and Yersinia intermedia occurred sporadically. Resistome analysis identified antimicrobial resistance genes (AMRG), including blaOXA variants, particularly in older appliances, indicating a potential domestic reservoir of resistance. The findings underscore the need for clearer household recommendations on refrigerator hygiene and temperature control, and advance our understanding of the microbial communities occuring in household refrigerators and its implications for consumer health, thereby contributing to improved domestic food safety.