Identification of Klebsiella oxytoca using a specific PCR assay targeting the polygalacturonase pehX gene

Bacteria of the genus Klebsiella are important opportunistic pathogens responsible for nosocomial infections that are increasingly resistant to antimicrobial agents. Distinctive identification of the species K. oxytoca, K. pneumoniae, K. planticola, K. ornithinolytica and K. terrigena is difficult based on phenotypic tests and misidentifications are frequent in routine clinical microbiology. We developed a specific method to discriminate K. oxytoca from the other species of the genus Klebsiella, based on the PCR amplification of the polygalacturonase ( pehX) gene. A PCR amplicon of 344 bp was obtained in all 35 K. oxytoca strains tested, but in none of the 29 K. pneumoniae, 12 K. planticola/K. ornithinolytica and 7 K. terrigena strains tested. The test was also negative for polygalacturonate-degrading species of the genus Erwinia. Analysis of 24 strains designated as K. pneumoniae from international collections (NCTC, PZH) revealed previous misidentification of six K. oxytoca strains. Key biochemical tests fully confirmed the pehX PCR results. The new K. oxytoca identification assay should be useful for both clinical and ecological monitoring of K. oxytoca strains, as well as for controlling the previous identification of collection strains.