Deletion of phoQ gene decreases the resistance of Pseudomonas aeruginosa to aminoglycoside antibiot-ics
Objective To analyze the sequences of two component signaling system PhoP/PhoQ encoding genes of Pseudomonas aeruginosa strains sensitive or resistant to aminoglycoside antibiotics and to determine the correlation between the PhoQ/PhoP and the resistance. Methods The segments of entire pimQ and phoP genes of P. aeruginosa were obtained by PCR and then sequenced after T-A cloning. Two prokaryotic expression systems of phoQ and phoP genes were constructed and the target recombinant expres-sion products rPhoQ and rPhoP were extracted by Ni-NTA chromatography. Rabbits were intracutaneoualy immunized with rPhoQ and rPhoP to obtain antisera and double immunodiffusion test was used to detect the titers of antisera. The phoQ genes of aminloglycoside antibiotics-resistant P. aeruginosa strains were knocked out by using Red recombination system, and phoQ mutants were identified by PCR plus sequencing and Western blot assay. Tube dilution method was applied to determine MIC values of wild and mutant strains of P. aeruginosa to four different aminoglycoside antibiotics. Results In comparison with the corresponding sequences in GenBank, the similarities of nueleotide and putative amino acid sequences of the cloned phop and phoQ genes were 98.7%-99.6% and 98.7%-100% , and 98.4%-99.8% and 99.1%-100%, respec-tively. Both rPhoQ and rPhoP were successfully expressed using pET-42a and E. coil BL21 DE3 system, and their rabbit antisera with 1 : 4 and 1 : 8 double immunodiffusion titers were also obtained. The deletion of phoQ genes and absence of the products in the two phoQ mutants were confirmed by PCR, sequencing and West-ern blot assay. MIC values of the four different aminoglycoside antibiotics to the two mutants were 1/512-1/2048 as those of their wild strains. Conclusion PboQ/PhoP is a sequence conserved two component sig-naling system of P. aeruginosa, and this system mediates resistance of the microbe to aminoglycoside antibiotics. 
 
Key words: 
Pseudomonas aeruginosa; phoQ/phoP genes; Gene knock out; Aminoglycoside anti-biotics