DNA adenine methylation modulates pathogenicity of Klebsiella pneumoniae genotype K1.

BACKGROUND/PURPOSE: Klebsiella pneumoniae genotype K1 is a highly virulent pathogen that causes liver abscess and metastatic endophthalmitis/meningitis. Whether its pathogenicity is controlled by DNA adenine methylase (Dam), an epigenetic regulator of bacterial virulence gene expression, is yet unknown. We aimed to study the role of DNA adenine methylation in the pathogenicity of K. pneumoniae genotype K1.

METHODS: We identified the dam gene in the prototype tissue-invasive strain (NTUH-K2044) of K. pneumoniae genotype K1, using the strain's complete genome sequence in GenBank. We constructed a dam- mutant and compared it with the wild type, in terms of in vitro serum resistance and in vivo BALB/cByl mice inoculation.

RESULTS: Loss of Dam activity in the mutant was verified by MboI restriction digestion of the genomic DNA and a 1000-fold increase in spontaneous mutation rate. The dam mutant lost at least 68% of serum resistance when compared with the wild type (survival ratio at 1 hour: 2.6 ± 0.4 vs. 8.2 ± 1.9; at 2 hours: 3.9 ± 1.6 vs. 17.4 ± 3.6; p values < 0.05). Likewise, virulence to mice decreased by 40-fold in an intraperitoneal injection model [lethal dose, 50% (LD50): 2 × 103 colony-forming units (CFUs) vs. 5 × 101 CFUs] and by sixfold in a gastric ingestion model (LD50: 3 × 104 CFUs vs. 5 × 103 CFUs). Attenuation of the dam mutant was not attributable to its growth rate, which was similar to that of the wild type.

CONCLUSION: Our results support the view that DNA adenine methylation plays an important role in modulating the pathogenicity of K. pneumoniae genotype K1. The incomplete attenuation indicates the existence of other regulatory factors.