Establishment of a young mouse model and identification of an allelic variation of zmpB in complicated pneumonia caused by Streptococcus pneumoniae

Objective: Complicated pneumonia, including necrotizing pneumonia,
lung abscess, and empyema, caused by Streptococcus pneumoniae
in children has been increasing. We thus determined to
investigate its virulence in an animal model and to identify virulence
factors of S. pneumoniae.
Design: Prospective, randomized, controlled animal study.
Setting: University medical laboratory.
Subjects: Male Balb/c-strain mice, 3 wks old.
Interventions: We used a young mouse model to monitor
bacterial virulence and a microarray to compare gene expression
between S. pneumoniae from children with complicated and noncomplicated
pneumonia. Deletion and complementation of a candidate
gene were performed to study its role on the virulence of
S. pneumoniae.
Measurements and Main Results: A model of complicated
pneumonia in young mice infected with strains of S. pneumoniae
from children with complicated pneumonia was established. Using
a microarray analysis, differences in zinc metalloprotease B
(zmpB) RNA hybridization between two strains from children with
complicated pneumonia (NTUH-p28 and NTUH-p15) and a strain
(NTUH-p3) from a child with pneumococcal lobar pneumonia were
found. Confirmatory assays revealed the signal differences were
due to sequence variation in the zmpB gene. Infection with the
zmpB deletion mutant of NTUH-p15 showed a significant decrease
in the severity of pneumonia and no destructive lung injury. The
zmpB complementation strain of NTUH-p15 significantly restored
the level of inflammation and caused lung necrosis. For studying
the effect of allelic variation of zmpB on the virulence of S.
pneumoniae, we added zmpB of NTUH-p15 in the zmpB deletion
mutant of NTUH-p3, which resulted in a higher bacterial burden
than that in wild-type NTUH-p3.
Conclusions: A young mouse model is established for complicated
pneumococcal pneumonia. This model proved that allelic
variation of zmpB affects the virulence of S. pneumoniae. (Crit
Care Med 2008; 36:1248–1255)