RESUMEN
Objective:To investigate the mechanism of polymyxin resistance related to lipopolysaccharide modification in carbapenem-resistant Klebsiella pneumoniae (CRKP). Methods:Plasmid-mediated drug resistance genes in seven CRKP strains were detected by conjugation assay and mcr gene detection. The expression of polymyxin resistance-related genes was measured using quantitative real-time PCR. The complete genomes of CRKP strains were sequenced. Silver staining and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) were performed to analyze the changes in lipopolysaccharide (LPS). Results:The seven CRKP strains were negative for mcr genes and the results of conjugation assay were also negative. Moreover, no mobile genetic elements related to drug resistance were detected. Compared with wild-type strain, all seven CRKP strains that were resistant to polymyxin showed increased expression of pmrA, pmrB and pmrC genes at the transcriptional level; six showed increased expression of phoP/ phoQ genes; three showed decreased expression of crrA/ crrB genes; four showed decreased expression of mgrB gene. The missense mutation sites in drug-resistant strains were mainly in KPHS_09430, KPHS_35900, KPHS_39520 and KPHS_52420. IS Kpn14 insertion sequence was detected in CRKP-6 strain. MALDI-TOF-MS reveals the modification of natural lipid A with L-Ara4N in CRKP LPS. Conclusions:LPS modification induced by chromosome-mediated mutation in the two-component regulatory system was the main molecular mechanism of polymyxin resistance in CRKP isolates in this study. Effects of the mutation in the two-component system on polymyxin resistance varied in different strains.
RESUMEN
Objective@#To investigate the molecular mechanism of colistin resistance in Klebsiella pneumoniae (K.pneumoniae).@*Methods@#Three clinical isolates of colistin-resistant K. pneumoniae (FK1149, FK1920 and FK1934) and three colistin-resistant mutants (FK660R, FK713R and FK729R) were investigated. Resistance genes of pmrAB, phoPQ, mgrB, crrAB, mcr-1 and mcr-2 were detected by PCR and then analyzed by sequencing. PROVEAN platform was used to predict changes in the biological functions of proteins related to drug resistance. Expression of pmrH, pmrC, mgrB and phoP genes was measured using quantitative real-time PCR. LPS silver staining and conjugation assay were performed to analyze the three clinical colistin-resistant isolates.@*Results@#Amino acid substitutions in PmrA (G53V), PmrB (T157P, R256G), MgrB (F44C) and CrrB (E189K) were detected. ISkpn14 and IS5-like insertion sequences were detected in FK713R and FK729R, respectively. FK1149, FK1920 and FK1934 were negative for mcr genes. Compared with the wild-type strain, expression of pmrH and pmrC genes at the transcriptional level was increased in all investigated isolates. Changes in the expression of phoP and mgrB genes were also observed. A partial deletion of LPS was identified in FK1149.@*Conclusion@#LPS modification induced by inactivation of PmrAB or MgrB is the main molecular mechanism of colistin resistance in K. pneumoniae isolates in this study. Mutations in PmrA (G53V), MgrB (F44C) and CrrB (E189K) that might be related to colistin resistance are detected for the first time in clinical isolates of K. pneumoniae.
RESUMEN
Objective To investigate the inhibitory effects of aloin on the growth of Staphylococcus aureus and its virulence factors α-hemolysin in vitro.Methods Broth dilution was used to measure the minimum inhibitory concentration (MIC) of water-soluble aloin on S.aureus.Agar drilling method was used to observe the size of inhibition zone of aloin for S.aureus.Plasma coagulase test was used to detect the changes of S.aureus coagulase and absorbance was measured to detect the changes of hemolytic activity when S.aureus was exposed to aloin.Real time PCR was used to detect the effects of aloin on the expressions of hla and agrA mRNA.Results The soluble aloin inhibited the growth of S.aureus in a dose-dependent manner.The inhibition zone diameter of a standard strain of S.aureus (ATCC 25923) was 21.5 mm with MIC of 12.5 mg/mL and 17 mm for the clinical isolate SA1.5 with MIC of 15 mg/mL.After treated with soluble aloin,the coagulase titers of ATCC 25923 were 16,4 and 2 for 1/2 MIC,1 MIC and 2 MIC respectively compared with titer 32 of the control group without soluble aloin.The expression of α-hemolysin of S.aureus ATCC 25923 was down-regulated by soluble aloin and the hemolytic activity of S.aureus ATCC 25923 with 1/2 MIC,1 MIC and 2 MIC groups were (77.4 ±3.41) ％,(42.2 ± 2.4) ％ and (38.7 ± 2.4) ％ respectively.The expression levels of hla were 0.020 3 (0.019 6,0.028 8),0.011 6(0.010 6,0.013 1) and 0.033 7(0.020 2,0.042 9) respectively in the 1/2 MIC,1 MIC and 2 MIC group respectively,and there were significant differences among the three groups (H =16.807,P ＜ 0.05).The expression levels of agrA was 0.074 6 (0.066 2,0.098 2),0.020 8 (0.012 2,0.032 6) and 0.021 3 (0.010 2,0.029 6) in the 1/2 MIC,1 MIC and 2 MIC group respectively,and there were significant differences among the three groups (H =16.320,P ＜ 0.05).Conclusion Aloin may inhibit the growth of S.aureus and could effectively inhibit the expression of α-hemolysin.
RESUMEN
Pseudomonas sp. M18, one of plant-growth-promoting rhizobacteria, can produce secondary metabolites including phenazine-1-carboxylic acid (PCA) and pyoluteorin (Plt). PA2572 gene coding protein is a probable two-component response regulator in Pseudomonas according to homologous speculations. In order to investigate its genetic function, PA2572 homologous gene, ppbR, was amplified from M18 genome, inactivated by inserting a Gm cassette. The resulting reconstruct was introduced into the M18 genome using homologous recombination technique, so as to obtain the null mutant M18P. The results showed that the M18P has less flagellar swimming and swarming motility, and yielded fewer PCA. The production of PCA was only 50% of the wild type. However, there was no remarkable difference between mutant and wild type in producing pyoluteorin in KMB medium.