Mechanisms of resistance of <I>Pseudomonas aeruginosa</I> to 4-quinolones were investigated by examining the outer membrane proteins and DNA gyrases of resistant clinical isolates. Minimum inhibitory concentrations (MIC) were determined for fluoroquinolones, imipenem, β-lactams, gentamicin and tetracycline. Ciprofloxacin was the most active quinolone followed by ofloxacin and norfloxacin. Resistant clinical isolates had an MIC to ciprofloxacin of 4mg/l or greater, and resistance was shown to be stable after 20 passages on nutrient agar in all but one of the isolates. In several isolates cross resistance with imipenem and β-lactams was seen. All clinical isolates were resistant to tetracycline. Outer membrane profiles of sensitive and resistant strains of <I>P.aeruginosa</I> were examined and shown to be variable. In highly resistant strains, resistance to 4-quinolones could not be attributed to a particular membrane protein alteration as the isolates were not paired. Low level quinolone resistance in a series of paired isolates was linked with an increase in expression of a 48kD protein, and ceftazidime resistance with the appearance of a 42kD protein. These proteins were found to be non-covalently associated with peptidoglycan suggesting that they may function as porins. DNA gyrases from 22 clinical strains were isolated from a novobiocin/sepharose column and assayed by electrophoresis. The level where quinolones inhibited 50% of DNA gyrase supercoiling activity on relaxed pBR322 (IC<SUB>50</SUB>), was determined for ciprofloxacin, ofloxacin and norfloxacin in all strains. In general the IC<SUB>50</SUB> concentrations were equivalent to or greater than, the MIC of each drug.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660836 |
| Date | January 1994 |
| Creators | Quibell, Kristen Jane |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/20129 |
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