Preliminary study on resistance mechanism and virulence features in carbapenems-resistant Klebsiella pneumoniae from burn patients

Objective To investigate resistance mechanism and virulence features of carbapenems-resistant Klebsiella pneumoniae (CRKP) and to provide theoretical foundation for the prevention and control of nosocomial infections in burn wards as well as clinical therapy of CRKP. Methods Strains of Klebsiella pneumoniae isolated from clinical samples of burn patients hospitalized in our unit from February to December 2016 were collected. The diameters of inhibition zone of imipemen or meropenem susceptibility disk of the above strains were≤22 mm. Kirby-Bauer disk diffusion method and automated instrument were applied to test drug resistance of the strains to 17 antibiotics of cephalosporins, aminoglycosides, sulfonamides, quinolones, and carbapenems. Pulsed-field gel electrophoresis (PFGE) was used to analyze homology of the strains. Crystal violet staining was applied to assess ability of biofilm formation of the strains. The hypermucoviscosity (HM) phenotype of the strains was determined by string test. Polymerase chain reaction was used to detect common carbapenemase genes of bla_KPC, bla_IMP, bla_OXA-48, and bla_NDM, capsular serotype genes of K1, K2, and K57, and virulence-associated gene of rmpA. Results (1) A total of 29 CRKP strains were isolated. The 29 CRKP strains were with high drug resistance rate to carbapenems antibiotics of imipenen, meropenem, and ertapenem, and cephalosporins, aminoglycosides, and quinolones antibiotics, while the strains were with low drug resistance rate to sulfonamides antibiotics and tegafycline. (2) The 29 CRKP strains had 4 types of A, B, C, and D according to PFGE, with 11 strains of type A, 10 strains of type B, 6 strains of type C, and 2 strains of type D. (3) Among the 29 CRKP strains, 25 strains were positive in biofilm formation, with positive rate of 86.2%. (4) None of the 29 CRKP strains was positive in the string test with HM phenotype. (5) All the 29 CRKP strains carried carbapenemase genes. Among the 29 CRKP strains, 11 strains carried both bla_NDM-1 and bla_OXA-48 genes, 1 strain carried both bla_NDM-1 and bla_KPC-2 genes, 12 strains only carried bla_KPC-2 gene, and 5 strains only carried bla_NDM-1 gene. The 79.3% (23/29) strains were completely resistant to 3 kinds of carbapenems antibiotics. (6) Among the 29 CRKP strains, 3 strains carried K2 gene, 2 of which were completely resistant to 3 kinds of carbapenems antibiotics, 1 strain carried rmpA gene, and no strain carried K1 or K57 gene. Conclusions The detection rate of CRKP isolated from burn patients hospitalized in our unit is high. The strains are mostly extensively drug-resistant bacteria, and the mechanism of drug resistance of which is complicated. There may have clonal spread of CRKP. And appropriate measures should be taken timely and effectively to prevent nosocomial spread of CRKP.