Infection of a hip prosthesis by Actinomyces naeslundii

We present the case of a 77-year-old woman who developed an Actinomyces nae slundii infection of a hip prosthesis. The isolate grew well aerobically wi th 5% CO2. Possible diagnostic problems may arise in the microbiological la boratory because aerobic growth is not sufficiently accounted for in some o f the traditional identification schemes and commercial test kits. Therefor e, besides presenting an unusual pathogen in this setting, this report focu ses on possible diagnostic problems in the microbiological laboratory.