Detection of prosthetic hip infection at revision arthroplasty by immunofluorescence microscopy and PCR amplification of the bacterial 16S rRNA gene

In this study the detection rates of bacterial infection of hip prostheses by culture and nonculture methods were compared for 120 patients with total hip revision surgery. By use of strict anaerobic bacteriological practice during the processing of samples and without enrichment, the incidence of i nfection by culture of material dislodged from retrieved prostheses after u ltrasonication (sonicate) was 22%. Bacteria were observed by immunofluoresc ence microscopy in 63% of sonicate samples with a monoclonal antibody speci fic for Propionibacterium acnes and polyclonal antiserum specific for Staph ylococcus spp. The bacteria were present either as single cells or in aggre gates of up to 300 bacterial cells. These aggregates were not observed with out sonication to dislodge the biofilm. Bacteria were observed in all of th e culture-positive samples, and in some cases in which only one type of bac terium was identified by culture, both coccoid and coryneform bacteria were observed by immunofluorescence microscopy. Bacteria from skin-flake contam ination were readily distinguishable from infecting bacteria by immunofluor escence microscopy. Examination of skin scrapings did not reveal large aggr egates of bacteria but did reveal skin cells. These were not observed in th e sonicates. Bacterial DNA was detected in 72% of sonicate samples by PCR a mplification of a region of the bacterial 16S rRNA gene with universal prim ers. All of the culture-positive samples were also positive for bacterial D NA. Evidence of high-level infiltration either of neutrophils or of lymphoc ytes or macrophages into associated tissue was observed in 73% of patients. Our results indicate that the incidence of prosthetic joint infection is g rossly underestimated by current culture detection methods. It is therefore imperative that current clinical practice with regard to the detection and subsequent treatment of prosthetic joint infection be reassessed in the li ght of these results.