Synthesis and activities of pyoverdin-quinolone adducts: a prospective approach to a specific Therapy against Pseudomonas aeruginosa

Pseudomonas aeruginosa is particularly resistant to most all the antibiotics presently available, essentially because of the very low permeability of its outer membrane. To overcome this, we synthesized four siderophore-based antibiotics formed by two quinolones - norfloxacin and benzonaphthyridone - bound to the pyoverdin of P. aeruginosa ATCC 15692 via two types of spacer arms: one stable and the other readily hydrolyzable. From the comparison of their antibacterial properties with those of the two unbound quinolones, we reached the following conclusions: (a) The adducts inhibit Escherichia coli's gyrase showing that the dissociation of the compounds is not necessary for their activity. However, the presence of the pyoverdin moiety on the molecule decreases the inhibition activity compared to the antibiotic alone. (b) They facilitate the uptake of (55)Fe using the specific pyoverdin-mediated iron-transport system of the bacterium. No uptake was observed either with P. aeruginosa ATCC 27853, which produces a structurally different pyoverdin, or with P. aeruginosa K690, which is a mutant of P. aeruginosa ATCC 15692 lacking FpvA, the outer-membrane pyoverdin receptor. (c) MIC determinations have shown that only strains P. aeruginosa ATCC 15692 and the derived outer-membrane receptor-producing but pyoverdin-deficient P. aeruginosa IA1 mutant present higher susceptibility to the pyoverdin-quinolone adducts, whereas P. aeruginosa ATCC 27853 and K690 are much more resistant. (d) Growth inhibition by these adducts confirmed these results and showed that the adducts with the hydrolyzable spacer arm have better activity than those with the stable one and that the labile spacer arm adducts present much higher activity than the quinolones alone. These results show clearly that the penetration of the antibiotic into the cells is favored when this latter is coupled with pyoverdin: Only the strains possessing the appropriate outer-membrane receptor present higher susceptibility to the adduct. In this case the antibiotic uses the pyoverdin-mediated iron-transport system. Furthermore, better efficiency is obtained when the spacer arm is labile and favors the antibiotic release inside the cell, allowing better inhibition of gyrase.

A novel, double mutation in DNA gyrase A of Escherichia coli conferring resistance to quinolone antibiotics

A spontaneous Escherichia coli mutant, named Q3, resistant to nalidixic acid was obtained from a previously described clinical isolate of E. coli, Q2, resistant to fluoroquinolones but susceptible to nalidixic acid (E. Cambau, F. Bordon, E. Collatz, and L. Gutmann, Antimicrob. Agents Chemother. 37:1247-1252, 1993). Q3 harbored the mutation Asp82Gly in addition to the Gly81Asp mutation of Q2. The different mutations leading to Gly81Asp, Asp82Gly, and Gly81AspAsp82Gly were introduced into the gyrA gene harbored on plasmid pJSW102, and the resulting plasmids were introduced into E. coli KNK453 (gyrAts) by transformation. The presence of Asp82Gly or Gly81Asp alone led to a low-level resistance to fluoroquinolones but not to nalidixic acid resistance. When both mutations were present, resistance to both nalidixic acid and fluoroquinolones was expressed. Purified gyrases of the different mutants showed similar rates of supercoiling. Dominance of the various gyrA mutant alleles harbored on plasmids was examined. The susceptibility to quinolones associated with wild-type gyrA was always dominant. The susceptibility to nalidixic acid expressed by the Gly81Asp mutant was dominant, while that expressed by the Asp82Gly mutant was recessive. From these results, we hypothesize that some amino acids within the quinolone resistance-determining region of gyrase A are more important for the association of subunits rather than for the activity of the holoenzyme.

Sequence analysis, purification, and study of inhibition by 4-quinolones of the DNA gyrase from Mycobacterium smegmatis

We determined the nucleotide sequence of a 6-kb DNA region harboring the recF, orf192, gyrB, and gyrA genes from Mycobacterium smegmatis mc(2)155. The amino acid sequences deduced from gyrA and gyrB displayed 89 and 86% identity, respectively, with the DNA gyrase from Mycobacterium tuberculosis, and 67 and 65% identity, respectively, with that from Streptomyces coelicolor. An open reading frame encoding the C-terminal region of the M. smegmatis RecF polypeptide was found upstream from gyrB and was 57% identical to the open reading frame encoding the C-terminal region of the S. coelicolor RecF protein. The gene orf192 was identified between recF and gyrB and was 39% identical to orf191 found in S. coelicolor in the recF-gyrB region. The M. smegmatis DNA gyrase, which was purified by affinity chromatography on novobiocin-Sepharose, consisted of two polypeptides with apparent molecular masses of 98 and 80 kDa. Determination of the N-terminal amino acid sequence of the B subunit confirmed GTG as the start codon in gyrB. Analysis of the supercoiling activity of the enzyme indicated that the M. smegmatis DNA gyrase was characterized by a specific activity equivalent to that of the Escherichia coli DNA gyrase. Inhibition of this activity by 4-quinolones was investigated by determining the 50% inhibitory concentrations (IC50S) of nalidixic acid, ofloxacin, and ciprofloxacin. The results indicated that the inhibitory activities of these drugs against the M. smegmatis DNA gyrase were markedly lower than those previously reported for the E. coli DNA gyrase. The results also suggested that the higher levels of activity of ofloxacin and ciprofloxacin against M. smegmatis (MICs, 0.5 to 1 microgram/ml), in contrast to that of nalidixic acid (MIC, 256 micrograms/ml), could be related to the higher inhibitory activities of fluoroquinolones against the DNA gyrase from this species (IC50S, 7 to 14 micrograms/ml) compared with that of nalidixic acid (IC50, 1,400 micrograms/ml).

Resistance to fluoroquinolones in Escherichia coli isolated from poultry

Quinolone-resistant Escherichia coli strains were isolated from poultry clinical samples in Saudi Arabia. The poultry flocks had been treated with oxolinic acid or flumequine prophylaxis. The measure of the uptake of fluoroquinolones showed that none of the strains had a reduced accumulation of quinolones. The result of complementation with the wild-type E. coli gyrA gene, which restored fluoroquinolone susceptibility, and the isolation of DNA gyrase from six isolates indicated that the resistant strains had an altered DNA gyrase. The minimum effective dose of ciprofloxacin for inhibition of supercoiling catalyzed by the isolated gyrases varied from 0.085 microgram/ml for a susceptible isolate (MIC < 4 micrograms/ml) up to 96 micrograms/ml for the more resistant one (strain 215, MIC > 64 micrograms/ml). For the same two isolates, the minimum effective doses of sparfloxacin varied from 0.17 up to 380 micrograms/ml. The in vitro selection of spontaneous single-step fluoroquinolone-resistant mutants using ciprofloxacin suggested that the more resistant mutants are likely the result of several mutations. These results also show that, as in human medicine, cross-resistance between older quinolones and fluoroquinolones can exist in veterinary isolates and reiterate the need for the prudent use of these drugs.

Sequential mutations of gyrA in Escherichia coli associated with quinolone therapy

A clinical isolate of Escherichia coli HM73 (MIC norfloxacin 2 mg/L) was isolated during norfloxacin therapy from an urinary tract infection in a patient who had been previously treated with pipemidic acid and infected by E. coli HM72 (norfloxacin 0.25), known to harbour a substitution Ser 83-->Leu in the gyrA gene. No difference in accumulation of norfloxacin was found between the two strains. DNA gyrases were isolated by affinity chromatography and assayed for supercoiling activity in the presence of norfloxacin. The minimal effective doses (MEDs) were 20 mg/L, for HM72 and 80 for HM73. DNA sequencing identified in HM73, two mutations leading to substitutions Ser 83 to Leu and Asp 87 to Gly.