Synthesis of kanamycin A derivatives by regioselective masking drug resistant enzymes targeting hydroxyl groups

The 3＇-OH, 4＇-OH and 2＂-OH of kanamycin A were modified in search of new aminoglycosides to overcome resistant enzymes, ANTs and APHs. The key intermediate was a dibenzylidene-protected derivative of kanamycin A. The aimed sites were masked by benzyl, methyl and allyl groups. Multi-step reactions gave the desired aminoglycoside derivatives but showed less antibiotic activity than kanamycin A.

Effect of Lanthanum on Disease Resistance Related Enzymes of Rape

The effects of lanthanum on the protective enzymes of rape ( Brassica juncea ) were studied in hydroponics experiment. Results show that when treated with 0.3 mg·kg -1 La, the content of chlorophyll and the activities of peroxidase(POD), catalase(CAT), superoxide dismutase(SOD) and polyphenoloxidase(PPO) in rape increase, but the content of malondialdehyde(MDA) in rape decreases. However, the treatments do not change the content of soluble protein in rape significantly.

Biochemical and Physiological Changes of Three Watermelon Cultivars Infested with Fusarium oxysporum f.sp.niveum

The dynamic changes in membrane permeability, activities of disease-related enzymes, and contents of pathogenesis-relevant chemical compounds and photosynthetic pigments in root cells of three watermelon cultivars were studied after inoculation with Fusarium oxysporum f. sp. niveum at seedling stage. The results showed that the capacity of self-regulating and returning to normal status of cultivar Kelunsheng (resistant) was greater than that of a susceptible cultivar, Zaohua, in terms of malonaldehyde (MDA) content, relative conductivity, and activity of superoxide dismutase (SOD) and catalase (CAT). The resistant cultivar maintained a higher activity of dehydrogenase, higher content of vitamin C(Vc) , and relatively lower content of soluble sugar than the susceptible cultivar. The content of soluble protein was higher in the resistant cultivar than that in the susceptible one at day 1 after inoculation. The capacities of the resistant cultivar to inhibit chlorophyll deterioration and maintain a higher carotenoid content were significantly stronger than those of the susceptible cultivar.

Study of Klebsiella pneumoniae producing extendedspectrum β-lactamases against aminoglycosides

Klebsiella pneumoniae （ K. pneumoniae） is one of the main gmn-negative bacilli in clinical practice. Nosocomial infections caused by K. pneumoniae producing extended-spectrum β-lactamases （ESBLs） are very difficult to treat. This paper investigated the resistant characteristics of K. pneumoniae producing ESBLs and their aminoglycoside-modifying enzyme gene expressions including Nacetyltransferases and O-adenyltransferases. Bacteria identification and ESBLs confirmatory tests were performed by Phoenix^TM-100 system. And minimum inhibitory concentrations （MICs） of gentamicin, amikacin, kanamycin, tobranycin, netilmicin and neomycin in 53 K. pneumoniae isolates were detected by agar dilution. In addition, six aminoglycoside-modifying enzyme genes were amplified by polymerase chain reaction （PCR） and verified by DNA sequencer. It was found that imipenem and meropenem against 120 K. pneumoniae isolates produced powerful antimicrobial activities. The resistant rates of gentamicin and amikacin were 55.0% and 46.7%, respectively. Except neomycin, MIC50 and MIC90 of gentamicin, amikacin, kanamycin, tobramycin and netilmicin in 53 K. pneumoniae were all 〉 128 μg/ml, and the resistant rates were 83.0%, 52.3%, 75.5%, 81.1% and 69.8%, respectively. However, neomycin was only 39.6%. In addition, five modifying enzyme genes, including aac（3）-Ⅰ, aac（3）-Ⅱ, aac（6＇）-Ⅰb, ant（3＂）-Ⅰ, ant（2＂）-Ⅰ genes, were found in 53 isoaltes except aac （6＇）-Ⅱ, and their positive rates were 11.3%, 67.9%, 47.2%, 1.9% and 39.6%, respectively. It was also confirmed by nucleotide sequence analysis that the above resistant genes shared nearly 100% identities with GenBank published genes. The results obtained in the present study indicated that K. pneumoniae producing ESBLs strains are rapidly spreading in our hospital, and their resistance to aminoglycosides may be associated with aminoglycoside-modifying enzyme gene expressions.

Relationship between antimicrobial resistance and aminoglycoside-modifying enzyme gene expressions in Acinetobacter baumannii

Background Acinetobacter baumannii is one of the main gramnegative bacilli in clinical practice Nosocomial infections caused by multidrug resistance Acinetobacter baumannii is very difficult to treat This study was designed to investigate the antimicrobial resistance characteristics and four resistant gene expressions of aminoglycosidemodifying enzymes including Nacetyltransferases and Ophosphotransferases in Acinetobacter baumannii Methods Bacterial identification and antimicrobial susceptibility test were performed by PhoenixTM system in 247 strains of Acinetobacter baumannii Minimal inhibitory concentrations (MICs) of seven aminoglycosides including gentamicin, amikacin, kanamycin, tobramycin, netilmicin, neomycin and streptomycin in 15 strains of multidrug resistant Acinetobacter baumannii were detected by agar dilution Four aminoglycosidemodifying enzyme genes were amplified by polymerase chain reaction (PCR) and verified by DNA sequencerResults The resistance rates of 247 strains of Acinetobacter baumannii against cefotaxime, levofloxacin, piperacillin, aztreonam, tetracycline, ciprofloxacin and chloramphenicol were more than 50% Imipenem and meropenem showed high antibacterial activities with resistance rates of 32% and 41% MIC50 and MIC90 of gentamicin, amikacin, streptomycin and kanamycin in 15 strains of multidrug resistant Acinetobacter baumanii were all more than 1024 mg/L, and the resistance rates were 100%, 100%, 100% and 933%, respectively But their resistance rates to tobramycin, netilmicin and neomycin were 867%, 933% and 467%, respectively Three modifying enzyme genes, including aacC1, aacC2 and aacA4 genes, were found in 15 strains, but aphA6 had not been detected Their positive rates were 933%, 200% and 200%, respectively These three genes existed simultaneously in No19 strain Nucleotide sequences of aacC1, aacC2 and aacA4 genes shared 100%, 979% and 997% identities with GenBank genes (AY307113, S68058 and AY307114)Conclusion Multidrug resistant Acinetobacter baumannii strains are rapidly spreading in our hospital, and their resistance to aminoglycosides may be associated with aminoglycosidemodifying enzyme gene expressions