Objective      To analyze the adhesion and cell virulence of Klebsiella pneumonia wild type(WT) strain

complemented strain c-Δcrp(cAMP receptor protein) and mutant strain Δcrp

in order to investigate crp gene on the adhesion and cell toxicity of Klebsiella pneumonia.        Methods      After infection of A549 cells by Klebsiella pneumonia WT strain

c-Δcrp strain and Δcrp strain

the cells were lysed and the bacteria were quantified by plating appropriate dilutions on Luria-Bertani agar plates. LDH release was detected to estimate cell activity

. Infection time and MOI were optimized.       Results      The adhesion ability of Klebsiella pneumonia WT (log

CFU

=5.145) and c-Δcrp strain (log

CFU

=4.915) was higher than that of Δcrp strain (log

CFU

=4.122) (P=0.004). The optimal conditions to determinate the LDH release included infected cells incubation for 8 h at 37 ℃

the developing time for 10 min in dark

and 1∶10 dilution of the supernatant for test. The virulence of WT strain (70.69%) was significantly higher than that of Δcrp strain (19.54%) (P=0.001).       Conclusion      Knocking-out of crp gene causes obvious decrease of cellular toxicity and adhesion

comparing with the WT strain and c-Δcrp strain. Klebsiella pneumonia CRP protein positively regulates bacterial virulence and adhesion.