Genetic Manipulation of Klebsiella pneumoniae

AcrAB-TolC efflux pump overexpression and tet(A) gene mutation increase tigecycline resistance in Klebsiella pneumoniae

Tigecycline-non-susceptible Klebsiella pneumoniae (TNSKP) is increasing and has emerged as a global public health issue. However, the mechanism of tigecycline resistance remains unclear. The objective of this study was to investigate the potential role of efflux pump system in tigecycline resistance. 29 tigecycline-non-susceptible Klebsiella pneumoniae (TNSKP) strains were collected and their minimum inhibitory concentrations (MIC) were determined by the broth microdilution method. The ramR, acrR, rpsJ, tet(A), and tet(X) were amplified by polymerase chain reaction (PCR). The mRNA expression of different efflux pump genes and regulator genes were analyzed by real-time PCR. Additionally, KP14 was selected for genome sequencing. KP14 genes without acrB, oqxB, and TetA were modified using suicide plasmids and MIC of tigecycline of KP14 with target genes knocked out was investigated. It was found that MIC of tigecycline of 20 out of the 29 TNSKP strains decreased by over four folds once combined with phenyl-arginine-β-naphthylamide dihydrochloride (PaβN). Most strains exhibited upregulation of AcrAB and oqxAB efflux pumps. The strains with acrB, oqxB, and tetA genes knocked out were constructed, wherein the MIC of tigecycline of KP14∆acrB and KP14∆tetA was observed to be 2 µg/mL (decreased by 16 folds), the MIC of tigecycline of KP14ΔacrBΔTetA was 0.25 µg/mL (decreased by 128 folds), but the MIC of tigecycline of KP14∆oqxB remained unchanged at 32 µg/mL. The majority of TNSKP strains demonstrated increased expression of AcrAB-TolC and oqxAB, while certain strains showed mutations in other genes associated with tigecycline resistance. In KP14, both overexpression of AcrAB-TolC and tet(A) gene mutation contributed to the mechanism of tigecycline resistance.

Cultivation and Genomic DNA Extraction of Klebsiella pneumoniae

Klebsiella pneumoniae is a Gram-negative, rod-shaped bacterium of medical significance. It typically exists as part of the normal flora of the human intestine but can cause severe infections in the healthcare setting due to its rapid acquisition of antibiotic resistance. Cultivating and extracting genomic DNA from this bacterium is crucial for downstream characterization and comparative analyses. To provide a standardized approach for growing K. pneumoniae in the laboratory setting, this collection of protocols provides step-by-step procedures for routine culturing, generating growth curves, storing bacteria, and extracting genomic DNA. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Reviving K. pneumoniae from frozen stocks Basic Protocol 2: Cultivating K. pneumoniae in rich growth medium Alternate Protocol: Cultivating in minimal liquid growth medium Basic Protocol 3: Enumerating K. pneumoniae colony forming units Basic Protocol 4: Growth curves Basic Protocol 5: Genomic DNA extraction Basic Protocol 6: Characterizing K. pneumoniae strains based on genomic sequence Basic Protocol 7: Storage of K. pneumoniae frozen stocks in glycerol Basic Protocol 8: Storage of K. pneumoniae in agar stabs.