Disruption of the smpB Gene in Acinetobacter baumannii: Effects on Biofilm Formation, Motility, Antibiotic Susceptibility, and Virulence

Acinetobacter baumannii is a highly adaptable pathogen notorious for its resistance to multiple antibiotics, posing significant challenges in clinical settings. A key factor in its adaptability is the ribosome rescue mechanism mediated by the small protein B (SmpB), in conjunction with transfer-messenger RNA (tmRNA), facilitating the rescue of stalled ribosomes. In this study, we disrupted the smpB gene in A. baumannii using the CRISPR/Cas9 system to investigate the effects on growth, motility, biofilm formation, antibiotic susceptibility, virulence, and proteomic profiles. The smpB mutant strain displayed significantly reduced biofilm formation and twitching motility compared to the wild-type strain, indicating that smpB plays a pivotal role in surface movement and biofilm production. Alterations in antibiotic susceptibility were observed, with increased sensitivity to gentamicin and piperacillin-tazobactam in the mutant strain. Proteomic analysis revealed downregulation of key proteins, including ribosomal proteins such as small ribosomal subunit protein uS7 and ATP synthase subunit b, which are involved in protein synthesis and energy production. Additionally, upregulation of proteins such as ribosome maturation factor, tRNA uridine(34) hydroxylase, and phenylalanine--tRNA ligase alpha subunit was noted, highlighting compensatory adjustments in ribosome maturation and amino acid metabolism. In a Galleria mellonella infection model, the smpB mutant exhibited reduced virulence compared to the wild-type strain. These findings emphasize the essential role of the smpB gene in A. baumannii pathogenicity and suggest that targeting the ribosome rescue system, particularly SmpB, could provide novel therapeutic strategies against multidrug-resistant infections