A Response to Article “Distribution of Mcr-1 Harboring Hypervirulent Klebsiella Pneumoniae in Clinical Specimens and Lytic Activity of Bacteriophage KpnM Against Isolates” [Letter]

We really appreciate the authors and all collaborators who have recently reported their research results in an article entitled “Distribution of Mcr-1 Harboring Hypervirulent Klebsiella Pneumoniae in Clinical Specimens and Lytic Activity of Bacteriophage KpnM Against Isolates”.Citation1 This study had shown very encouraging research results and important information regarding the use of bacteriophage; KpnM phage in this case, which could be further studied for combating the antibiotic resistance issues. However, first of all, this study lacks clear determination of “hypervirulent” bacteria.Citation2,Citation3 The phenotypes of hypervirulent K. pneumoniae isolates could be observed via microscopic examinations.Citation4 Take the observation of thick capsules formation or hyperfimbriae formation on the bacterial cells as examples.Citation5,Citation6 Since the authors would like to address the hypervirulence in K. pneumoniae isolated in this study, the measurement of CPS staining observed under microscope or EPS/eDNA quantification would give a more comprehensive explanation, instead of showing the mucoid colonies cultured on LB or MacConkey agar show. in Figure 1A and B, for most K. pneumoniae strains show a mucoid colony phenotype especially when cultured on MacConkey agar at 37 °C. In Figure 1C the string test was mentioned as the hypervirulence phenotype test of the clinical K. pneumoniae isolates. Although the string test was performed well on the MacConkey agar, the required controls; such as the classical K. pneumoniae strain or virulent gene deletion mutant of K. pneumoniae, were excluded. The extracellular polysaccharide (EPS) related gene deletion mutants which lose their ability to form the mucoid colony phenotype could be the proper control for this type of assay.Citation7,Citation8 In addition, the string test result should also mention at least the average length of the string resulting from the hyper virulence in an understandable unit, thereafter being compared to the control, or at least being statistically compared to the antibiotic(s) susceptible K. pneumoniae isolates