Rapid identification of capsular serotype K1/K2 Klebsiella pneumoniae in pus samples from liver abscess patients and positive blood culture samples from bacteremia cases via an immunochromatographic strip assay

BACKGROUND: In Asia, serotype K1/K2 Klebsiella pneumoniae are the major capsular serotypes that cause liver abscess or bacteremia in patients. The purpose of this study was to compare novel immunochromatographic strips (ICSs), which can rapidly detect K. pneumoniae serotypes K1/K2 in clinical samples, to conventional capsular serotyping methods. METHODS: Pus drainage samples from 16 patients with a liver abscess caused by K. pneumoniae, blood samples from 112 positive flagged blood culture bottle and a subsequent single colony in the medium were tested with the ICS. The results were then compared to findings of capsular swelling tests. Samples subjected to the polymerase chain reaction (PCR) analysis were used as reference. RESULTS: The identification of K. pneumoniae via the traditional bacterial culture from pus samples took 3.4 days on average (ranging from 2.2 to 5.5 days). Further capsular serotyping of K. pneumoniae by the capsular swelling test of pure isolates lasted 5–10 min, and the PCR method took ~ 4 h. As for ICSs, the time for direct identification of the K. pneumoniae capsular serotype K1/K2 in pus was < 4 min (ranging from 2 to 4 min). The results of ICSs were consistent with capsular swelling tests and PCR methods. Testing of 112 blood culture samples and subsequent single colonies in the medium with ICSs yielded consistent results for most samples. CONCLUSIONS: This study indicates that ICSs can rapidly detect K. pneumoniae serotypes K1 and K2 in pus or positive flagged blood culture broth samples within 5 min. Their accuracy is comparable to that of the conventional capsular serotyping methods such as a serum agglutination assay or PCR.