Misidentification of Raoultella spp. (R. terrigena, R. planticola) and Klebsiella spp. (K. variicola, K. grimontii) as Klebsiella pneumoniae: Retrospective study of a necropsy-associated bacterial collection from horses

Misidentifications as Klebsiella pneumoniae were observed during a French retrospective study of a necropsy-associated K. pneumoniae bacterial collection from horses. Accordingly, the present study aimed to further characterise the 12 Raoultella spp. and Klebsiella spp. strains involved in these misidentifications. The strains were identified and characterised using the Api 20E system, K. pneumoniae PCR detection, matrix-assisted laser desorption/ionisation time-of-flight mass spectroscopy and whole-genome sequencing. Antimicrobial susceptibilities were tested by the disc diffusion method with a panel of 40 antibiotics. Thus, misidentifications as K. pneumoniae mainly concerned Raoultella spp. (R. terrigena, R. planticola) rather than Klebsiella spp. (K. variicola, K. grimontii), with a dominance of R. terrigena. Among the 12 strains, only K. grimontii was multi-drug resistant and none were considered hypervirulent. MALDI-TOF was sufficient to avoid misidentification but commercial spectra databases should be expanded with K. grimontii and R. terrigena reference spectra to improve identification accuracy. This is probably (i) the first report of K. grimontii and R. planticola isolations from horses and (ii) the second report of R. terrigena and K. variicola isolations from horses.