Introduction: Since its first description in 2003, clinical case reports have repeatedly
documented that the bacterial species Kerstersia gyiorum is a human pathogen. K.
gyiorum has been described in the context of wound and middle ear infections, has
been found in urine samples, and has even been recognized as a causative agent of
septicemia. However, the pathogenic potential of K. gyiorum cannot be clearly deter
mined due to the current lack of information about this species. To reveal the clinical
significance of K. gyiorum, it is therefore essential to first create a clearly defined refer
ence collection of isolates obtained from routine clinical diagnostics.
Methods: The aim of this study is to determine the most appropriate method
for identifying K. gyiorum in routine diagnostics. To this end, three widely used
routine methods (VITEK 2, MALDI-TOF MS, and 16S rRNA gene sequencing) were
employed, and the accuracy of their results for K. gyiorum identification was
compared. To ensure accurate species identification, dDDH (an NGS-based iden
tification strategy) was used as the reference method. Furthermore, this manu
script provides an overview of all cases reported in the literature to date and
discusses the accuracy of the identification results reported in these studies. In
addition, genomic studies (pangenome and ANI matrix) were conducted using in
silico analyses to investigate the clonal relationships among the isolates.
Results: The results show that MALDI-TOF MS is best suited for identifying K. gyiorum
in routine diagnostics. However, in contrast to most publications, 16S rRNA gene
sequencing was not suitable, as it was impossible to distinguish K. gyiorum from other
members of the Alcaligenaceae family. The VITEK 2 system must also be considered
unreliable for the correct identification of K. gyiorum. Additionally, this study identified
a candidate for an undescribed species of the genus Kerstersia.
Discussion: MALDI-TOF MS is well suited for expanding the reference collection
directly from routine diagnostics. The results of 16S gene sequencing should be inter
preted with caution. Conversely, biochemical methods must be regarded as unreli
able. The species’ large core genome suggests a specialized previously unknown
specialized ecological niche. Furthermore, two distinct clusters within the reference
collection suggest a common origin. Additionally, follow-up studies must determine
whether one isolate that cannot be unambiguously assigned to a species represents
a previously undescribed member of the genus Kerstersia.