ClumpingFaktor

ClumpingFaktor, or clumping factor, is a term used in microbiology to describe a class of surface-anchored proteins found in Staphylococcus aureus that promote the clumping of bacteria in plasma by binding to host fibrinogen. The best-characterized members are ClfA and ClfB. ClumpingFaktors belong to the MSCRAMM family (microbial surface components recognizing adhesive matrix molecules) and function as adhesins that mediate interaction with host proteins and contribute to colonization and immune evasion.

These proteins are anchored to the bacterial cell wall by an LPXTG motif and are exported to the surface via sortase enzymes. Their N-terminal A domains bind fibrinogen, facilitating cross-linking of fibrinogen molecules and aggregation of bacterial cells when plasmalike environments are encountered. Through binding to fibrinogen, ClumpingFaktors also enhance adherence to damaged tissue, indwelling medical devices, and platelets, supporting invasive disease in some infections.

Expression of ClumpingFaktor genes is influenced by global regulatory networks and environmental cues, including stationary phase signals and iron availability. In clinical contexts, ClfA and related factors contribute to the virulence of S. aureus by promoting endocarditis, bacteremia, and pneumonia in severe infections. Their presence can be exploited in diagnostic assays, such as latex agglutination tests, to identify S. aureus isolates, and they have been explored as targets for vaccine development and therapeutic antibodies to attenuate virulence.

The term ClumpingFaktor reflects the historical observation that these proteins cause visible clumping of bacteria in plasma, a phenomenon that aided early recognition of this virulence mechanism.