Abstract
Klebsiella is a genus of Gram-negative bacteria known to be opportunistic pathogens that may cause a variety of infections in humans. Highly drug-resistant Klebsiella species, especially K. pneumoniae, have emerged rapidly and are becoming a major concern in clinical management. Although K. pneumoniae 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 Klebsiella spp. in community-onset infections by WGS of clinical isolates (n = 105) collected during a prospective sepsis study in Sweden. The sequencing revealed that 32 of the 82 isolates (39.0%) initially identified as K. pneumoniae 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 Klebsiella variicola and nine as other members of the K. pneumoniae complex. Comparisons of the number of resistance genes showed that significantly fewer resistance genes were detected in Klebsiella oxytoca compared to K. pneumoniae and K. variicola (both values of p < 0.001). Moreover, a high proportion of the isolates within the K. pneumoniae complex were predicted to be genotypically multidrug-resistant (MDR; 79/84, 94.0%) in contrast to K. oxytoca (3/16, 18.8%) and Klebsiella michiganensis (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 Klebsiella spp. with ST14 (10.0%) and ST5429 (10.0%) as the most prevalent ones for K. pneumoniae, ST146 for K. variicola (12.0%), and ST176 for K. oxytoca (25.0%). In conclusion, the results from this study highlight the importance of using high-resolution genotypic methods for identification and characterization of clinical Klebsiella spp. isolates. Our findings indicate that infections caused by other members of the K. pneumoniae complex than K. pneumoniae are a more common clinical problem than previously described, mainly due to high rates of misidentifications.
Highlights
The Gram-negative bacteria Klebsiella possess a major threat to public health, causing significant morbidity and mortality worldwide
A total of 105 bacterial isolates were identified as Klebsiella spp., whereof 82 isolates were identified as K. pneumoniae, two isolates as K. variicola, and 21 isolates as K. oxytoca (Figure 1)
Due to previous reports pointing out the inability of conventional microbiology laboratory techniques to differentiate between Klebsiella spp. (Long et al, 2017a; Rodríguez-Medina et al, 2019), genotypic species identification of the collected isolates was performed by calculating the pairwise average nucleotide identity (ANI) on the assembled Illumina short-read data against reference genomes
Summary
The Gram-negative bacteria Klebsiella possess a major threat to public health, causing significant morbidity and mortality worldwide. Many related Klebsiella spp. have been identified and classified leading to an expansion of the taxonomy of the K. pneumoniae complex. K. pneumoniae is the major cause of infections within the complex, the involvement in human infections of the other species is gaining recognition (Seki et al, 2013; Brisse et al, 2014; Maatallah et al, 2014; Holt et al, 2015; Breurec et al, 2016; Chen et al, 2016; Ejaz et al, 2017; Long et al, 2017b; Nicolás et al, 2018).
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