Analysis of the Type VI secretion system and microbiological characteristics of hypervirulent Klebsiella pneumoniae causing urinary tract infections

INTRODUCTION: This study aimed to evaluate the Type VI secretion system (T6SS) and microbiological features in hypervirulent Klebsiella pneumoniae (hvKP) causing urinary tract infections (UTIs) in hospitalized adults. METHODOLOGY: This retrospective, observational analysis encompassed 167 inpatients with UTIs caused by KP. The study investigated disease prevalence, antimicrobial susceptibility, gene carriage rates, and competition indices. Strains were classified as classic KP (cKP), T6SS-positive hvKP, or T6SS-negative hvKP, and compared for clinical traits, antimicrobial susceptibilities, and virulence gene carriage. Furthermore, the bacterial competition index of T6SS-positive hvKP strains was assessed through in vitro cultivation. RESULTS: Of 167 patients, 82 had hvKP and 85 had cKP. hvKP had higher rates of thrombosis, immunotherapy, hypoproteinemia, and longer hospital stays (p < 0.05). The 30-day mortality was 29.26% for hvKP vs. 12.94% for cKP (p = 0.045). hvKP showed highest resistance to cefuroxime (81.70%) and cKP to ampicillin/sulbactam (56.47%), with low resistance to tigecycline. The resistance to carbapenems (carbapenem-resistant KP, CR-KP) was significantly higher in hvKP compared to cKP (30.48% vs 16.47%, p = 0.032). Aerobactin and iroB differed between hvKP and cKP. T6SS-positive hvKP had higher rates of thrombosis and immunotherapy (p < 0.05). The 30-day mortality was 9.52% for T6SS-positive vs. 36.06% for T6SS-negative (p = 0.043). T6SS-positive hvKP strains exhibited lower resistance to carbapenems compared to T6SS-negative strains (9.52% vs 37.70%, p = 0.015). T6SS-positive strains had higher aerobactin and iroB positivity. CONCLUSIONS: T6SS-positive hvKP exhibits lower antimicrobial resistance but stronger virulence, playing a major role in bacterial competition.