Phage therapy has shown great promise in the treatment of bacterial infections. However, the effectiveness of phage therapy is compromised by the inevitable emergence of phage-resistant strains. In this study, a phage-resistant Carbapenem-Resistant Klebsiella pneumoniae (CRKP) strain SWKP1711R, derived from parental CRKP strain SWKP1711 was identified. The mechanism of bacteriophage resistance in SWKP1711R was investigated and the molecular determinants causing altered growth characteristics, antibiotic resistance, and virulence of SWKP1711R were tested. Compared to SWKP1711, SWKP1711R showed slower growth, smaller colonies, filamentous cells visible under the microscope, reduced production of capsular polysaccharide (CPS) and lipopolysaccharide (LPS), and reduced resistance to various antibiotics accompanied by reduced virulence. Adsorption experiments showed that phage vB_kpnM_17-11 lost the ability to adsorb onto SWKP1711R, and the adsorption receptor was identified to be bacterial surface polysaccharides. Genetic variation analysis revealed that, compared to the parental strain, SWKP1711R had only one thymine deletion at position 78 of the open reading frame of the lpcA gene, resulting in a frameshift mutation that caused alteration of the bacterial surface polysaccharide and inhibition of phage adsorption, ultimately leading to phage resistance. Transcriptome analysis and quantitative reverse transcriptase PCR (qRT-PCR) revealed that genes encoding LPS synthesis, ompK35, blaTEM-1, and type II and Hha-TomB toxin antitoxin (TA) systems, were all downregulated in SWKP1711R. Taken together, the evidence presented here indicate that the phenotypic alterations and phage resistance displayed by the mutant may be related to the frameshift mutation of lpcA and altered gene expression. While evolution of phage resistance remains an issue, our study suggests that the reduced antibiotic resistance and virulence of phage-resistant strain derivatives might be beneficial in alleviating the burden caused by multidrug-resistant bacteria.Copyright © 2024. Published by Elsevier Ltd.