Fungal-Bacterial Interactions in Health and Disease

Abstract

Fungi and bacteria encounter each other in various niches of the human body. There, they interact directly with one another or indirectly via the host response. In both cases, interactions can affect host health and disease. In the present review, we summarized current knowledge on fungal-bacterial interactions during their commensal and pathogenic lifestyle. We focus on distinct mucosal niches: the oral cavity, lung, gut, and vagina. In addition, we describe interactions during bloodstream and wound infections and the possible consequences for the human host.

Keywords: antagonism; commensals; cross-kingdom interactions; microbiome; mixed infections; mycobiome; polymicrobial; synergism.

Figure 3

Microbial communities in mouth, lung, gut, and vagina of healthy humans. Most frequently identified bacterial (left) and fungal (right) genera are listed alphabetically and sorted by niche. Identification by culture and sequencing were considered [5,7,17,18,44,45,46,47,48,49,50,51,52,53,54].

Figure 1

From dysbiosis to damage. Fungal-bacterial interactions can be beneficial or detrimental for the host. (A) High microbial diversity keeps individual fungal and bacterial species under control. Upon reduced diversity, due to, for example, antibiotics, certain species grow to increased abundance. (B) In low-diversity populations, opportunistic microbes switch from commensal to pathogen. (C) During co-infection, fungi and bacteria promote each other’s virulence, for example, by joined tissue penetration.

Figure 2

Modes of fungal-bacterial interaction. Fungi and bacteria interact via different modes of action. Direct binding leads to physical interaction. Release or consumption of chemical compounds, such as metabolic byproducts or quorum sensing molecules, mediates communication in a confined environment. Consumption of oxygen or release of protons influences the local milieu. Fungi and bacteria compete for nutrients or binding sites in a certain niche. Upon proliferation, mixed biofilms are assembled.