Analysis of drug resistance genes and molecular typing of carbapenem-resistant Klebsiella variicola strains / 中华微生物学和免疫学杂志

ABSTRACT

Objective To investigate the prevalence and drug resistance of clinical Klebsiella vari-icola ( K. variicola ) isolates and to illuminate the mechanism of drug resistance in carbapenem-resistant strains. Methods Clinical K. variicola isolates were identified with matrix-assisted laser desorption/ioniza-tion time-of-flight mass spectrometry ( MALDI-TOF MS ) . The antimicrobial susceptibility profile of these strains was determined using broth microdilution. Resistance genes carried by carbapenem-resistant K. vari-icola strains were detected by PCR with specific primers. Multilocus sequence typing ( MLST) was used for molecular typing. A pan-drug resistant strain which was isolated from cerebrospinal fluid sample was ana-lyzed with whole genome sequencing ( WGS) . Results Twenty-six isolates were identified as K. variicola by MALDI-TOF MS. Results of the antimicrobial susceptibility test showed that there were 15. 4％ (4/26) re-sistant to carbapenem and 11. 5％ (3/26) unsusceptible to tigecycline. These strains were highly suscepti-ble to amikacin and gentamicin, which accounted for 96. 2％ (25/26). As for the third-and fourth-genera-tion cephalosporins, the resistance rate was 23. 1％ (6/26). All of the four carbapenem-resistant isolates carried the resistance genes of blaIMP-4 , qnrA/B and blaTEM , and one of them was also positive for blaNDM-1 gene. The fosfomycin resistance gene, fosA, was detected in three of them. Molecular typing analysis indica-ted these isolates belonged to two sequence types ( ST) of ST357 ( three strains) and ST1737 ( one strain) . Two plasmids were obtained from the pan-drug resistant strain by WGS, including IncFⅡ/FIB( k) type plas-mid (160 kb) that was highly homologous to LMG 23571 plasmid (GenBank: CP013986. 1) and IncHⅠ1B/FIB type plasmid (260 kb) sharing high homology with pIMP4 LL34 (GenBank: CP025964. 1). Be-sides the resistance genes mentioned above, the two plasmids also carried a variety of other genes that media-ted the resistance to aminoglycosides (strB, strA, armA, aac3-Ⅱd, aadA2), macrolides (msrE, mphE), chloramphenicol (catA2), sulfonamides (sulⅠ) tigecycline (tetA variant) and trimethoprim (dfrA16). However, no virulence genes were detected. Conclusions In general, the resistance profile of K. variicola was similar to that of Klebsiella pneumoniae, but the differences were that carbapenem-resistant K. variicola strains mainly belonged to ST357 and the leading causes of resistance were carrying the genes encoding IMP-4 and NDM-1 metalβ-lactamases. WGC analysis revealed that the pan-drug resistant K. variicola strain carried multiple drug resistance genes without virulence determinants, which might be resulted from the evo-lution of drug resistance.