Serotype K1
K. pneumoniae ST23 is, a highly virulent pathogenic strain causing invasive community-acquired infections, that is widespread in its geographical distribution in Asia [
5]. Fortunately, ST23 strains have shown good susceptibility to most antibiotics. However, the advent of multidrug resistance with high transmission potential in
K. pneumoniae serotype K1 causes serious concerns. A few strains of ESBL-producing serotype K1
K. pneumoniae have already been reported in Asian countries [
6,
7,
11]. In the present study, we report serotype K1
K. pneumoniae strains co-producing the PAB DHA-1 and ESBL. We found three isolates that were phenotypically ESBL producers, but we could not detect any
bla genes responsible for the ESBL phenotype. Therefore, other ESBL genotypes may be involved. In addition, two of the three isolates were identified as PAB. Recently, gram-negative organisms that produce both ESBLs and PAB enzymes have increasingly been described worldwide [
12‐
15]. To our knowledge, this is the first report of serotype K1
K. pneumoniae producing both ESBL and PAB. Both ESBLs and PAB enzymes are associated with broad, multidrug resistance because multiple antibiotic-resistance genes exist on the same plasmid [
16]. One isolate (KPN3) in our study showed carbapenem resistance in the broth microdilution test. Subsequently, we used PCR analysis to determine the presence of carbapenemase genes, such as
bla
IMP,
bla
VIM,
bla
OXA, and
bla
NDM; however, none of these genes were detected. The frequency of PAB transmission may be higher than initially thought, especially if the spread of resistance mimics the trend that we have seen occurring over the past few years for ESBLs. Moreover, porin alteration, combined with the production of ESBL or PAB, has been demonstrated to confer carbapenem resistance [
17,
18]. We also characterized antimicrobial susceptibility between non-serotype K1 and serotype K1 ESBL-producing
K. pneumoniae. Although the number of total isolates was too small to draw definite conclusions, the resistant rates of piperacillin-tazobactam and imipenem in K1 isolates tended to be high. It is uncertain whether the increase of antimicrobial resistance in serotype K1
K. pneumoniae is connected with any one particular resistance gene.
The emergence of multidrug-resistant strains with high transmission potential in serotype K1 K. pneumoniae is of great concern due to limited alternative treatment options and the possibility of global dissemination. Careful surveillance of resistant strains and adequate infection prevention and control measures are necessary.