23S PCR as a supplementary method for diagnosis of infectious arthritis. A prospective study

Abstract number: p1758

Moser  C., Andresen  K., Kjerulf  A., Salamon  S., Kemp  M., Christensen  J.J.

Objectives: 

Molecular methods for identification of infectious agents in patients with clinical infectious disease are increasingly being used. Especially in cases where antibiotics have been given prior to sampling or when fastidious bacteria difficult to grow are the aaetiology of the infection. Infectious arthritis is a serious disease where identification of the etiological agent is mandatory for optimal antibiotic treatment as well as indication of the primary focus if not the joint it self.

Methods: 

In the present prospective study, 227 synovial fluids taken from patients in elucidation of affected joints and sent to a Clinical Microbiological laboratory in the Copenhagen area, Denmark, were examined by conventional (culture, phenotypic tests) and molecular methods (PCR/sequencing of 23S ribosomal genes). Conventional methods included Gram-staining and microscopy, aerobic and anaerobic culture and identification. PCR/sequencing included DNA extraction, PCR assay which produced a 700 bp fragment of 23S rDNA, and sequencing of both DNA strands of the amplicons. Sequencing data were edited and a BLAST search in the NCBI database was done.

Results: 

Overall a microorganism was identified in 24 of the 227 synovial fluids (10.6%). In 14 synovial fluids from nine patients bacteria were identified by either methods [Staphylococcus aureus (n = 8), Streptococcus pneumoniae (n = 3), Streptococcus dysgalactiae (n = 2), Citrobacter freundii (n = 1)]. Six synovial fluids were only culture positive; in four of those six specimens coagulase negative staphylococci were isolated. In three of the 227 synovial fluids a microorganism was identified by 23S PCR only. In two synovial fluids 23S PCR identified only one microorganism, whereas culturing resulted in two isolates.

Conclusion: 

The present study indicates a significant contribution by molecular methods (PCR/sequencing of 23S ribosomal genes) in recognizing and identification of microorganisms from foci normally considered sterile like synovial fluids. Continued suspicion of infected arthritis despite of negative cultures should result in use of molecular diagnostics.