The type VI secretion system as a potential predictor of subsequent bloodstream infection of carbapenem-resistant Klebsiella pneumoniae strains on intestinal colonization.

BACKGROUND

The type VI secretion system (T6SS) has been recognized as a novel virulence factor in Klebsiella pneumoniae. This study investigated the occurrence of T6SS genes in carbapenem-resistant Klebsiella pneumoniae (CRKP) strains during intestinal colonization and evaluated their effect on the development of bloodstream infections.

METHODS

The study encompassed 2,385 patients admitted to the intensive care unit (ICU) and subjected to routine screening for intestinal colonization with CRKP. PFGE was employed on CRKP strains isolated from both the patients' intestine and blood cultures, confirming their genetic similarity. PCR was employed to detect the presence of carbapenemase genes, T6SS genes, and virulence genes. Quantitative real-time PCR was conducted to assess the expression levels of the core genes associated with the T6SS. The correlation between T6SS expression and sBSI was further investigated.

RESULTS

Approximately 10% (238/2385) of ICU patients tested positive for CRKP colonization. Among patients who tested positive, 10.1% (24/238) developed CRKP-sBSI. Patients carrying T6SS-positive CRKP isolates were more commonly linked to a history of invasive procedures, antibiotic use, and immunosuppression (P < 0.05), and were strongly associated with 28-day mortality (P < 0.001). It indicated that T6SS-positive CRKP strains exhibited a higher prevalence of virulence genes, such as rmpA and iucA, compared to T6SS-negative ones (P < 0.001). Compared to the strains isolated from simple colonization group, there was a significant increase in the mRNA expression of both hcp and vgrG genes (P < 0.05) of strains from the sBSI group, suggesting the key genes of the T6SS may play a significant role in the occurrence and progression of sBSI caused by CRKP.

CONCLUSION

The presence of the T6SS in a CRKP strain from intestinal colonization can serve as a promising predictive marker for sBSI. Conducting screenings for CRKP in patients' intestinal flora and monitoring T6SS carriage can improve the prevention and management of CRKP bloodstream infections.