Here, we present a case of an 85-year-old woman with a low-grade-infection caused by Actinomyces naeslundii after total-knee arthroplasty (TKA) followed by septic loosening. Actinomyces naeslundii was cultured from a tissue sample from the knee joint capsule/synovial tissue obtained after the initial TKA. A review of the literature revealed two cases of periprosthetic infection and another three cases of arthritis due to Actinomyces naeslundii. So far, no standard treatment for periprosthetic infections caused by Actinomyces species has been established.