Pathogenic Bacteria

Pathogenic bacteria are bacteria capable of causing disease in a host. Pathogenicity refers to this disease-causing capacity. Most bacteria are not pathogenic, and whether disease develops depends on both characteristics of the bacterium and the susceptibility and defenses of the host .^1,2

Pathogenic bacteria can cause disease through mechanisms associated with virulence. These can include attaching to host tissues, invading cells or deeper tissues, obtaining nutrients within the host, avoiding or resisting immune defenses, and producing toxins or other molecules that damage cells or alter normal host functions. The specific mechanisms differ considerably among bacterial species and strains .^1,2

Pathogenic bacteria are often distinguished as primary pathogens or opportunistic pathogens. Primary pathogens can cause disease in otherwise healthy hosts, although infection does not necessarily result in illness in every case. Opportunistic pathogens are more likely to cause disease when normal host defenses are weakened or disrupted, or when they gain access to body sites where they are not normally found .¹

Pathogenicity is distinct from virulence. Pathogenicity describes the capacity to cause disease, whereas virulence generally refers to the degree of disease-causing potential or severity associated with a pathogen in a particular context. Virulence can depend on bacterial characteristics as well as factors such as the route and dose of infection and the susceptibility of the host .¹