Revisiting the importance of virulence determinant magA and its surrounding genes in Klebsiella pneumoniae causing pyogenic liver abscesses: exact role in serotype K1 capsule formation.
BACKGROUND
Mucoviscosity-associated gene A (magA) is proposed to play a decisive role in the pathogenesis of liver abscesses due to Klebsiella pneumoniae. Although some investigators consider MagA to be a putative O-antigen ligase, it is also reportedly associated with the K1 antigen.


METHODS
Using magA-positive serotype K1 K. pneumoniae STL43 isolated from a patient with liver abscess, we constructed 3 bacterial mutants by targeting genes within the same transcription unit, including magA, wcaG, and rfbP. The virulence of these mutants was determined by neutrophil phagocytosis and inoculation of mice. Transmission electron microscopy and Western blot analysis were used to define their surface polysaccharides.


RESULTS
STL43 was resistant, and all 3 mutants were highly susceptible, to phagocytosis. None of the mutant strains caused death in mice at the lethal dose of STL43. In contrast to previous reports, transmission electron microscopy revealed that all 3 mutants were nonencapsulated. Analysis of surface polysaccharides revealed that all 3 mutants retained their O antigen but lost their K antigen/capsule. Furthermore, amino acid analysis showed that MagA shared a conserved domain of Wzy, the serotype-specific capsular polysaccharide polymerase.


CONCLUSIONS
In accordance with the bacterial polysaccharide gene nomenclature (BPGN) scheme, MagA should be renamed Wzy(KpK1), the capsular polymerase specific to K. pneumoniae serotype K1.
Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei, Taiwan, Republic of China.
Kuo-Ming
KM
Yeh
Jung-Chung
JC
Lin
Fon-Yi
FY
Yin
Chang-Phone
CP
Fung
Han-Chang
HC
Hung
Leung-Kei
LK
Siu
Feng-Yee
FY
Chang
D000328:Adult; D000818:Animals; D000942:Antigens, Bacterial; D016667:Bacterial Capsules / Q000235:genetics* / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D015153:Blotting, Western; D005798:Genes, Bacterial / Q000235:genetics* / Q000502:physiology; D006801:Humans; D007711:Klebsiella pneumoniae / Q000235:genetics / Q000472:pathogenicity*; D046290:Liver Abscess, Pyogenic / Q000382:microbiology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D016297:Mutagenesis, Site-Directed; D010587:Phagocytosis / Q000502:physiology; D011135:Polysaccharides, Bacterial; D016415:Sequence Alignment
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C501254:MagA protein, Klebsiella pneumoniae; D011135:Polysaccharides, Bacterial; C036962:capsular polysaccharide K1