Microbiological Characteristics Of Type Ⅵ Secretory System And Hypermucoviscous In Hypervirulent Klebsiella Pneumoniae Infected By Bloodstream Infections

PART I Role of type VI secretion system in the pathogenecity and drug resistance of Klebsiella pneumoniae isolates causing bloodstream infectionsObjective The type Ⅵ secretion system（T6SS）is a novel virulence factor of Klebsiella pneumoniae.This study aimed to investigate clinical and molecular characteristics of T6SS‐positive K.pneumoniae‐induced bloodstream infections（BSIs）.We also explored whether the T6 SS genotype is a useful prognostic marker of K.pneumoniae BSI mortality.Methods In this prospective analysis,we enrolled 119 individuals who had been diagnosed with K.pneumoniae bloodstream infection between July 2019 and January 2021 and acquired demographic and clinical data from their medical records.The capsule serotypes（K1 and K2）,virulence genes（rmp A,rmp A2,aerobactin,iro B）and T6 SS genes（hcp,vgr G,icm F）of all isolates were detected by polymerase chain reaction.In this study,strains that were positive for icm F and vgr G and hcp were designated as T6 SS positive.Hypervirulent Klebsiella pneumoniae（hv Kp）was defined as rmp A and aerobactin positivity.Five T6SS-positive and five T6SS-negative isolates were chosen for the competition,serum resistance,and biofilm formation experiments to further gain insights regarding the microbiological properties of T6SS-positive K.pneumoniae isolates.Results Among 119 isolates obtained from patients with BSIs,20（16.8%）were T6 SS positive K.pneumoniae.The incidence of virulence genes and K1 capsule serotype of T6 SS positive group were higher than that of T6 SS negative group.For hvkp,T6 SS positive group was significantly higher than T6 SS negative group（P = 0.001）.T6SS-positive isolates may be more competitive with Escherichia coli than T6SS-negative isolates.T6SS-positive isolates,in addition,did not show stronger biofilm-forming activity or a higher survival rate in the presence of normal human serum in comparison to T6SS-negative isolates.Conclusion T6 SS positive K.pneumoniae was common in people who had BSIs.T6 SS positive K.pneumoniae strains apparently looked more virulent.T6 SS positive K.pneumoniae strains had a lower rate of antimicrobial resistance in comparison to T6 SS negative strains.T6 SS positive isolates may be more competitive with Escherichia coli than T6 SS negative isolates.T6 SS positive isolates,on the other hand,did not show stronger biofilm-forming activity or a higher survival rate in the presence of normal human serum in comparison to T6 SS negative isolates.Part II Hypermucoviscous of Klebsiella pneumoniae and Its Relation with Serotyping,Virulence Genes,and Antimicrobial Treatment PatternObjective This study aimed to assess the predictive factors of bloodstream infection（BSI）due to hypermucoviscous Klebsiella pneumoniae（Hm KP）,distribution and treatment mode of virulence genes.Materials and Methods The medical records of 119 patients with Klebsiella pneumoniae bloodstream infection who were divided into the Hm KP（n=50）and non-Hm KP（n=69）groups and were retrospectively reviewed.Capsular serotyping（K1 and K2）and capsule-associated virulence genes（rmp A,rmp A2,aerobactin and iro B）were studied using the molecular method.Clinical data collected from the electronic medical record system included primary and secondary diagnosis,basic diseases,treatment and in-hospital mortality.Results Klebsiella pneumoniae isolates from bloodstream infection mainly came from inpatients in urology department（31;26%）,intensive medicine department（15;12.6%）,hematology department（17;14.2%）,and infection department ward（14;11.7%）.50（42.0%）isolates were positive in string test.The mortality did not differ between patients in the Hm KP bloodstream infection and non-Hm KP bloodstream infection groups.Patients with Hm KP infection were more likely to develop liver abscess than patients with non-Hm KP infection（20.0% vs 1.4%,P=0.001）.In addition,the incidence of ESBL in patients with Hm KP bloodstream infection was lower than that in patients with non-Hm KP bloodstream infection（6.0% vs 30.4%,P=0.001）.The incidence of virulence genes（rmp A,rmp A2 and iro B）of Hm KP group were higher than that of non-Hm KP group（P<0.05）.Conclusion Hypermucoviscous Klebsiella pneumoniae had a high frequency in isolates collected from patients with bloodstream infection.Our data support a statistical correlation between the hypermucoviscous Klebsiella pneumoniae and liver abscess in terms of abscess formation for these hypermucoviscous K.pneumoniae strains.Carbapenems and tegacyclin were the most common therapeutic options for the treatment of bloodstream infections with Klebsiella pneumoniae.Virulence genes rmp A,rmp A2 and iro B are closely related to Klebsiella pneumoniae.