Microbiological Characteristics And Clinical Features Of Serotype K57 Klebsiella Pneumoniae

Objective:1.To study the microbiological characteristics of serotype K57 klebsiella pneumoniae(K57-KP).2.Assess the clinical risk factors of K57-KP to provide scientific basis for both the rational preventive measures and the medical treatments.3.To characterize the molecular epidemiological and distribution of virulence genes of K57-KP.4.To investigate the virulence of K57-KP.Method: 1.Source of strain: The Klebsiella pneumoniae isolates of various samples from inpatients were collected during January 2014 to December 2016 from the First Affiliated Hospital of Nanchang University.Strains identification and antibiotic susceptibility testing were performed using the VITEK32 automatic bacteria identification system.Primer design according to the reference: polymerase chain reaction(PCR)and sequencing technologies were employed to screen non- repetitive K57-KP.The reference standards were used to screen hypervirulent Klebsiella pneumoniae strains,ie HvKP,and CKP.Moreover,features of the mucoid phenotype was confirmed in a wire drawing process.Also,the hydroxy- diphenyl colorimetric determination was used to test the quantity of capsular polysaccharide of the strains.All of the above mentioned experiments provided the information for us to fully understand the microbiological characteristics.2.The data of the above mentioned 39 patients infected with K57-KP strains were collected.Furthermore,the data of the following patients were also gathered: patients of the same gender;patients of similar age(±5 years old)and hospitalized in the same period,and clinically diagnosed with HvKP as well; non-HvKP infected patients.The ratio of these collected dataset was 1:1:2. Afterwards,the comparison is conducted to study age,blood glucose levels, primary diseases,invasive operations,history of operation,major trauma,and antibiotics usage before infection.Finally,based on the above statistics,the independent risk factors for K57-KP infection were found.3.We analyzed the molecular epidemiological characteristics and virulence gene distribution with four typing methods: pulsed-field gel electrophoresis(PFGE), multilocus sequence typing(MLST),wzi typing and polymerase chain reaction (PCR)amplified virulence gene analysis.4.On one hand,references measured the biofilm formation ability by the results obtained from anti-neutrophil phagocytosis assay,serum resistance test,crystal violet method.On the other hand,the virulence of the isolates was reflected based on the 50% lethality rate of infected mice in vitro.?Results:1.Among 39 strains of K57-KP,26 were positive for string test,and 39 strains of HvKP were positive for this test.K57-KP capsule polysaccharide content was significantly lower than HvKP,and CKP had no significant difference,HvKP capsular polysaccharide content was significantly higher than CKP.CKP showed high resistance to most commonly used antibiotics,and HvKP had a low resistance rate to most commonly used antibiotics,and K57-KP group had a resistance rate between the two.2.Univariate analysis showed that K57-KP was associated with CKP,with diabetes(P=0.011),drainage(P=0.004),carbapenem antibiotics(P=0.026),and quinolone antibiotics.(P=0.012)These factors were statistically significant.Multivariate analysis showed that K57-KP had diabetes compared with CKP(P=0.019,OR=3.549),drainage(P=0.030,OR=2.706),use of carbon Penememides(P=0.025,OR=2.753),quinolones(P=0.019,OR=3.049),and hepatobiliary disease(P=0.011,OR=3.263)were statistically significant.3,39 strains of K57-KP PFGE are mainly type A,ST type ST412 is 21,ST218 is type 6,ST592 type is 5,ST268 type is 3,ST161 and ST11 type are 2;K57-KP Wzi206-K57 was dominant,accounting for 58.97%,followed by wzi77-K57,accounting for 28.21%,there were 3 strains in wzi34-K57,and 1 strain in wzi57-K57 and wzi64-K57.The CPS content of strain ST412 in K57-KP was significant.Higher than non-ST412 strains,the content of CPS with different wzi typing was different;the detection rate of K57-KP rmpA,rmpA2,aerobactin,ybt was higher than that of CKP.Among the 39 strains of K57-KP,39 strains showed serum resistance,35 strains of HvKP and 9 strains of CKP.The neutrophil phagocytosis rate of K57-KP was significantly higher than that of HvKP(****P< 0.001),there was no significant difference in the phagocytosis rate of neutrophils with CKP(P=0.084),and the phagocytosis rate of K57-KP with different wzi types was different,among which the phagocytosis rate of wzi-K57 was the lowest;the K57-KP organism was the lowest;The membrane formation capacity was significantly higher than HvKP and lower than CKP.The biofilm formation ability of K57-KP with different wzi typing was different,among which the wzi57-K57 biofilm formation ability was the strongest;the LD50 value of K57-KP was 1.0 × 106.To 5.8 × 107,the LD50 value of HvKP is less than 1.0 × 102 to 1.2 × 105,and the LD50 value of CKP is between 1.3 × 107 and >1.0 × 108.conclusion:1.The positive rate of K57-KP and HvKP high drawing test was inconsistent with the low detection result of capsular polysaccharide;the resistance rate of K57-KP to commonly used antibiotics was increased compared with HvKP.2.Diabetics,drainage,use of carbapenems,and use of quinolone antibiotics are independent risk factors for K57-KP infection.3.The K57-KP in the First Affiliated Hospital of Nanchang University showed a high degree of homology;the ST412 strain had a stronger capsular polysaccharide synthesis ability than the non-ST412 strain;the same with K57-KP,its wzi score Different types of capsular polysaccharide content were different;the virulence gene carrying number of K57-KP was higher than that of CKP,lower than that of HvKP.4.The present study confirmed that the K57-KP virulence was lower than that of HvKP,higher than that of CKP,of which the virulence of wzi57-K57 was the strongest.K57-KP showed low virulence in a mouse model.