Genotypic Characterization of Clinical Klebsiella spp. Isolates Collected From Patients With Suspected Community-Onset Sepsis, Sweden

Abstract

<i>Klebsiella</i> is a genus of Gram-negative bacteria known to be opportunistic pathogens that may cause a variety of infections in humans. Highly drug-resistant <i>Klebsiella</i> species, especially <i>K. pneumoniae</i>, have emerged rapidly and are becoming a major concern in clinical management. Although <i>K. pneumoniae</i> is considered the most important pathogen within the genus, the true clinical significance of the other species is likely underrecognized due to the inability of conventional microbiological methods to distinguish between the species leading to high rates of misidentification. Bacterial whole-genome sequencing (WGS) enables precise species identification and characterization that other technologies do not allow. Herein, we have characterized the diversity and traits of <i>Klebsiella</i> spp. in community-onset infections by WGS of clinical isolates (<i>n</i> = 105) collected during a prospective sepsis study in Sweden. The sequencing revealed that 32 of the 82 isolates (39.0%) initially identified as <i>K. pneumoniae</i> with routine microbiological methods based on cultures followed by matrix-assisted laser desorption-time of flight mass spectrometry (MALDI-TOF MS) had been misidentified. Of these, 23 were identified as <i>Klebsiella variicola</i> and nine as other members of the <i>K. pneumoniae</i> complex. Comparisons of the number of resistance genes showed that significantly fewer resistance genes were detected in <i>Klebsiella oxytoca</i> compared to <i>K. pneumoniae</i> and <i>K. variicola</i> (both values of <i>p</i> < 0.001). Moreover, a high proportion of the isolates within the <i>K. pneumoniae</i> complex were predicted to be genotypically multidrug-resistant (MDR; 79/84, 94.0%) in contrast to <i>K. oxytoca</i> (3/16, 18.8%) and <i>Klebsiella michiganensis</i> (0/4, 0.0%). All isolates predicted as genotypically MDR were found to harbor the combination of β-lactam, fosfomycin, and quinolone resistance markers. Multi-locus sequence typing (MLST) revealed a high diversity of sequence types among the <i>Klebsiella</i> spp. with ST14 (10.0%) and ST5429 (10.0%) as the most prevalent ones for <i>K. pneumoniae</i>, ST146 for <i>K. variicola</i> (12.0%), and ST176 for <i>K. oxytoca</i> (25.0%). In conclusion, the results from this study highlight the importance of using high-resolution genotypic methods for identification and characterization of clinical <i>Klebsiella</i> spp. isolates. Our findings indicate that infections caused by other members of the <i>K. pneumoniae</i> complex than <i>K. pneumoniae</i> are a more common clinical problem than previously described, mainly due to high rates of misidentifications.