Journal of Microbiology

Review

[Minireview] Antibiotic resistance of pathogenic Acinetobacter species and emerging combination therapy: Bora Shin , Woojun Park; J. Microbiol. 2017;55(11):837-849. Published online October 27, 2017; DOI: https://doi.org/10.1007/s12275-017-7288-4

Abstract: The increasing antibiotic resistance of Acinetobacter species in both natural and hospital environments has become a serious problem worldwide in recent decades. Because of both intrinsic and acquired antimicrobial resistance (AMR) against last-resort antibiotics such as carbapenems, novel therapeutics are urgently required to treat Acinetobacter-associated infectious diseases. Among the many pathogenic Acinetobacter species, A. baumannii has been reported to be resistant to all classes of antibiotics and contains many AMR genes, such as blaADC (Acinetobacter-derived cephalosporinase). The AMR of pathogenic Acinetobacter species is the result of several different mechanisms, including active efflux pumps, mutations in antibiotic targets, antibiotic modification, and low antibiotic membrane permeability. To overcome the limitations of existing drugs, combination theraphy that can increase the activity of antibiotics should be considered in the treatment of Acinetobacter infections. Understanding the molecular mechanisms behind Acinetobacter AMR resistance will provide vital information for drug development and therapeutic strategies using combination treatment. Here, we summarize the classic mechanisms of Acinetobacter AMR, along with newly-discovered genetic AMR factors and currently available antimicrobial adjuvants that can enhance drug efficacy in the treatment of A. baumannii infections.

Research Support, Non-U.S. Gov't

Overexpression of Outer Membrane Protein OprT and Increase of Membrane Permeability in phoU Mutant of Toluene-Tolerant Bacterium Pseudomonas putida GM730: Kyunghee Lee , Juna Jung , Kwang Kim , Dongwon Bae , Dongbin Lim; J. Microbiol. 2009;47(5):557-562. Published online October 24, 2009; DOI: https://doi.org/10.1007/s12275-009-0105-y

Abstract: Eight toluene-sensitive mutants were previously isolated from the toluene-tolerant bacterium Pseudomonas putida GM730. One of these mutants was TOS6, in which Tn5 had been inserted into phoU. Susceptibility to multiple antibiotics, as well as toluene sensitivity, was increased in the phoU mutant of P. putida GM730. We compared the outer membrane proteins from the phoU mutant and wild-type via two-dimensional gel electrophoresis. A 45 kDa protein was dramatically overexpressed as the result of phoU inactivation, and this protein was identified by peptide mass fingerprinting and microsequencing as a conserved hypothetical protein consisting of 414 amino acids. The protein, designated as OprT, harbors a signal sequence and extended β-sheets, both of which are features common to the bacterial porins. The rate of ethidium bromide accumulation in TOS6 was higher than in GM730, which indicates that the TOS6 membranes may be more permeable to ethidium bromide than are the membranes of GM730. We propose that the toluene sensitivity and increased antibiotic susceptibility observed in the phoU mutant may be attributable to increased membrane permeability.

Iron Increases Susceptibilities of Pseudomonas aeruginosa to Ofloxacin by Increasing the Permeability: Sookyoung Kim , Jinsook Kim , Hyeran Nam , Yusun Jung , Yeonhee Lee; J. Microbiol. 2000;38(4):265-269.

Abstract: Iron increased the susceptibilities of clinical isolates of Pseudomonas aeruginosa to quinolones. In the presence of iron, increased susceptibilities to ofloxacin were observed in twenty-six out of thirty isolates and with no change in four isolates. In the case of norfloxacin, iron increased susceptibilities of twelve isolates but did not render any change in eighteen isolates. In the case of ciprofloxacin, iron decreased the MICs (Minimal Inhibitory Concentration) of twenty isolates, increased the MIC of one isolate, and did not change the MICs of nine isolates. To find out how iron increased susceptibility to ofloxacin, bacterial cells were grown in Muller Hinton (MH) media and succinate minimal media (SMM) to induce iron acquisition systems and the intracellular ofloxacin concentrations were assayed in the presence of iron. The addition of iron to the media decreased the MICs of cells whether they were grown in MH or SMM. Siderophores, carbonyl cyanide m-chlorophenylhydrazone (an inhibitor of proton motive force), and ouabain (an inhibitor of ATPase) did not decrease the effect of iron. Results suggested that the increase in the intracellular ofloxacin concentration by iron is accomplished not by decreasing the efflux but by increasing the ofloxacin permeability.

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