Epidemiology and molecular characteristics of the type VI secretion system in Klebsiella pneumoniae isolated from bloodstream infections.

BACKGROUND: The type VI secretion system (T6SS) has been identified as a novel virulence factor. This study aimed to investigate the prevalence of the T6SS genes in Klebsiella pneumoniae-induced bloodstream infections (BSIs). We also evaluated clinical and molecular characteristics of T6SS-positive K pneumoniae.

METHODS: A total of 344 non-repetitive K. pneumoniae bloodstream isolates and relevant clinical data were collected from January 2016 to January 2019. For all isolates, T6SS genes, capsular serotypes, and virulence genes were detected by polymerase chain reaction, and antimicrobial susceptibility was tested by VITEK® 2 Compact. MLST was being conducted for hypervirulent K. pneumoniae (HVKP).

RESULTS: 69 (20.1%) were identified as T6SS-positive K. pneumoniae among 344 isolates recovered from patients with BSIs. The rate of K1 capsular serotypes and ten virulence genes in T6SS-positive strains was higher than T6SS-negative strains (P = .000). The T6SS-positive rate was significantly higher than T6SS-negative rate among HVKP isolates. (P = .000). The T6SS-positive K. pneumoniae isolates were significantly more susceptible to cefoperazone-sulbactam, ampicillin-sulbactam, cefazolin, ceftriaxone, cefotan, aztreonam, ertapenem, amikacin, gentamicin, levofloxacin, and ciprofloxacin (P < 0.05). More strains isolated from the community and liver abscess were T6SS-positive K. pneumoniae (P < .05). Multivariate regression analysis indicated that community-acquired BSIs (OR 2.986), the carriage of wcaG (OR 10.579), iucA (OR 2.441), and p-rmpA (OR 7.438) virulence genes, and biliary diseases (OR 5.361) were independent risk factors for T6SS-positive K. pneumoniae-induced BSIs.

CONCLUSION: The T6SS-positive K. pneumoniae was prevalent in individuals with BSIs. T6SS-positive K. pneumoniae strains seemed to be hypervirulent which revealed the potential pathogenicity of this emerging gene cluster.