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Antimicrobial Agents and Chemotherapy, 08 1996, 1835-1842, Vol 40, No. 8
T Takenouchi, F Tabata, Y Iwata, H Hanzawa, M Sugawara and S Ohya
The elevated expression of the norA gene is responsible for efflux-
mediated resistance to quinolones in Staphylococcus aureus (E.Y.W. Ng, M.
Trucksis, and D.C. Hooper, Antimicrob. Agents Chemother. 38:1345- 1355,
1994). For S. aureus transformed with a plasmid containing the cloned norA
gene, SA113(pTUS20) (H. Yoshida, M. Bogaki, S. Nakamura, K. Ubukata, and M.
Konno, J. Bacteriol. 172:6942-6949, 1990), and an overexpressed mutant,
SA-1199B (G.W. Kaatz, S.M. Seo, and C.A. Ruble, J. Infect. Dis.
163:1080-1086, 1991), the MICs of norfloxacin increased 16 and 64 times
compared with its MICs for the recipient and wild-type strains, SA113 and
SA-1199, respectively. MICs of CS-940, however, increased only two and
eight times, even though these two fluoroquinolones are similarly
hydrophilic (apparent logPs of approximately -1). No good correlation was
found, among 15 developed and developing quinolones, between the increment
ratio in MICs and hydrophobicity (r = 0.61). Analysis of the quantitative
structure- activity relationship among 40 fluoroquinolones revealed that
the MIC increment ratio was significantly correlated with the bulkiness of
the C-7 substituent and bulkiness and hydrophobicity of the C-8 substituent
of fluoroquinolones (r = 0.87) and not with its molecular hydrophobicity (r
= 0.47). Cellular accumulation of norfloxacin in SA- 1199B was
significantly lower than that in SA-1199, and it was increased by addition
of carbonyl cyanide m-chlorophenyl hydrazone. On the other hand,
accumulations of CS-940 in these strains were nearly identical, and they
were not affected by addition of the protonophore.
Copyright © 1996 by the American Society for Microbiology. All rights reserved.
Hydrophilicity of quinolones is not an exclusive factor for decreased activity in efflux-mediated resistant mutants of Staphylococcus aureus
Biological Research Laboratories, Sankyo Co., Ltd., Tokyo, Japan.
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