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BACKGROUND: Nine gene clusters dedicated to nonribosomal synthesis of secondary metabolites with possible antimicrobial action, including polymyxin and fusaricidin, were detected within the whole genome sequence of the plant growth-promoting rhizobacterium (PGPR) Paenibacillus polymyxa M-1. To survey the antimicrobial compounds expressed by M-1 we analyzed the active principle suppressing phytopathogenic Erwinia spp. RESULTS: P. polymyxa M-1 suppressed the growth of phytopathogenic Erwinia amylovora Ea 273, and E. carotovora, the causative agents of fire blight and soft rot, respectively. By MALDI-TOF mass spectrometry and reversed-phase high-performance liquid chromatography (RP-HPLC), two antibacterial compounds bearing molecular masses of 1190.9 Da and 1176.9 Da were detected as being the two components of polymyxin P, polymyxin P1 and P2, respectively. The active principle acting against the two Erwinia strains was isolated from TLC plates and identified by postsource decay (PSD)-MALDI-TOF mass spectrometry as polymyxin P1 and polymyxin P2. These findings were corroborated by domain structure analysis of the polymyxin (pmx) gene cluster detected in the M-1 chromosome which revealed that corresponding to the chemical structure of polymyxin P, the gene cluster is encoding D-Phe in position 6 and L-Thr in position 7. CONCLUSIONS: Identical morphological changes in the cell wall of the bacterial phytopathogens treated with either crude polymyxin P or culture supernatant of M-1 corroborated that polymyxin P is the main component of the biocontrol effect exerted by strain M-1 against phytopathogenic Erwinia spp.

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Objective To investigate the resistant mechanism of quinolones on multi-drug resistant Klebsiella caused pneumonia(MDR-KPN).Methods From August 2008 to May 2010,47 strains of MDR-KPN were collected from 6 hospitals in Hangzhou and Huzhou in Zhejiang province in China.Drug target genes to quinolones (gyrA,parC) and quinolone-resistance genes mediated by mobile genetic elements [qnrA,qnrB,qnrS,aac (6')-Ⅰ b-cr,qepA] were analyzed by PCR and verified by DNA sequencing.Results Positive results were found in 47 strains of MDR-KPN,43 strains (91.5％) of gyrA mutation,40 strains(85.1％) ofparC mutation,3 strains (6.4％) of qnrB2,1 strain (2.1％) ofqnrB 4,8 strains (17.0％) ofqnrS 1,5 strains (10.6％) of qnrS 4,2 strains (4.3％)of aac (6')-Ⅰ b-cr respectively.Moreover,5 novel variants of gyrA (GenBank accession number:JN811952,JN811953,JN811954,JN811955,JN811956),5 novel variants of parC (GenBank accession number:JN817432,JN817433,JN817434,JN817435,JN817436)were also identified.In addition,qnrS4 (GenBank accession number:JN836269) appeared to be the novel variants of qnrS.Conclusion Quinolone-resistance-determining region played a key role on the resistance to quinolones in this group of MDR-KPN,and quinolone-resistance genes mediated by mobile genetic elements [qnrB2,qnrB4,qnrS1,qnrS4,aac (6')-Ⅰ b-cr] showed positive in some parts of the strains.This was the first report on emergence of qnrS4 in the world.