The usefulness of multiplex PCR for the identification of bacteria in joint infection.

backgroundThe diagnosis of septic arthritis (SA) relies on synovial analysis and conventional culture. But, these methods lack of sensitivity and culture is time consuming to establish a definite diagnosis. This study evaluated a new multiplex PCR assay which entailed screening PCR for Gram typing and identification PCR for species identification using two primer mixes.

methodsA total of 80 synovial fluid samples from patients with suspected SA were collected. Culture, multiplex PCR, and 16S rRNA gene PCR were performed.

resultsThe analytical sensitivity of multiplex PCR assay was 10(1) CFU/ml for each type of bacteria. There was no cross-reactivity with common bacterial pathogens. Bacteria were detected in 20, 25, and 26 of 80 samples for culture, multiplex PCR, and 16S rRNA gene PCR, respectively. Nineteen (95%) of 20 culture-positive samples and 6 (10%) of 60 culture-negative samples were positive for the multiplex PCR. Five of six samples which were positive only from multiplex PCR were also positive in 16S rRNA gene PCR. The multiplex PCR showed 2 false-negative in 27 true-positive samples but no false-positive. The sensitivity and specificity of the multiplex PCR were 92.6 and 100%, and the agreement with culture and 16S rRNA gene PCR were 91.3 and 96.3%, respectively. The time to detection for multiplex PCR was a maximum of 6 hr.

conclusionThis multiplex PCR assay offers high sensitivity and improved detection speed relative to culture. The appropriate combination of this new multiplex PCR assay with culture may contribute to the accurate and rapid diagnosis of SA.