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Notes: Abstract The resistance mechanisms to fluoroquinolones in Staphylococcus aureus were clarified by analyzing mutations in the genes encoding target enzymes, and examining the expression of the efflux pump, and determining the inhibitory activities of fluoroquinolones against the altered enzymes. Mutations in the grlA and gyrA genes of 344 clinical strains of S. aureus isolated in 1994 in Japan were identified by combinations of methods – single-strand conformation polymorphism analysis, restriction fragment length analysis, and direct sequencing – to identify possible relationships with fluoroquinolone resistance. Five types of single-point mutations and four types of double mutations were observed in the grlA gene in 204 strains (59.3%). Four types of single-point mutations and four types of double mutations were found in the gyrA gene in 188 strains (54.7%). Among these mutations, the grlA mutation of TCC → TTC or TAC (Ser-80 → Phe or Tyr) and the gyrA mutation of TCA → TTA (Ser-84 → Leu) were the principal ones, being detected in 137 (39.8%) and 121 (35.2%) isolates, respectively. A total of 15 types of mutation combinations within both genes were related to ciprofloxacin resistance (MIC ≧3.13 μg/ml) and were present in 193 mutants (56.1%). Strains containing mutations in both genes were highly resistant to ciprofloxacin (MIC50 =50 μg/ml). Those strains with the Ser-80 → Phe or Tyr alteration in grlA, but wild type in gyrA showed a lower level of ciprofloxacin resistance (MIC50≦12.5 μg/ml). Levofloxacin was active against 68 of 193 isolates (35.2%) with mutations at codon 80 of grlA in the presence or absence of concomitant mutations at codons 73, 84, or 88 in gyrA (MIC ≦6.25 μg/ml). Sitafloxacin (DU-6859a) showed good activity in 186 of 193 isolates (96.4%), with an MIC of ≦6.25 μg/ml. The contribution of membrane-associated multidrug efflux protein (NorA) expression to fluoroquinolone resistance was clarified by the checker-board titration method for determining the MIC of norfloxacin alone and in combination with carbonyl cyanide m-chlorophenylhydrazone. Among 344 clinical isolates, 139 strains (40.4%), in which the MIC of norfloxacin varied from 1.56 to 〉800 μg/ml, overexpressed the NorA protein. GrlA and GrlB proteins of topoisomerase IV, and GyrA and GyrB proteins of DNA gyrase encoded by genes with or without mutations were purified separately. The inhibitory activities of fluoroquinolones against the topoisomerase IV which contained a single amino acid change (Ser → Phe at codon 80, Glu → Lys at codon 84 of grlA, and Asp → Asn at codon 432 of grlB) were from 5 to 95 times weaker than the inhibitory activities against the non-altered enzyme. These results suggest that the mutations in the corresponding genes may confer quinolone resistance; the active efflux pump, NorA, was considered to be the third quinolone-resistance mechanism. The numerous and complicated mutations seen may explain the rapid and widespread development of quinolone resistance described in S. aureus. Sitafloxacin showed good antibacterial activity against ciprofloxacin- or levofloxacin-resistant mutants because of its high inhibitory activity against both topoisomerase IV and DNA gyrase.

Notes: Abstract Recent studies have indicated the key role of adenosine receptor activation as a trigger for ischemic preconditioning (PC). Hence, the augmentation of endogenous adenosine may potentiate the cardioprotective effects of PC. In this study, we aimed to test the hypothesis that dilazep dihydrochloride, an adenosine transport inhibitor, potentiates the PC effect. Protocol 1: Infarcts were produced in open-chest anesthetized rabbits by 30-min occlusion of a coronary artery and 2 days' reperfusion. PC was elicited by a preceding 5-min occlusion and either 5, 40, or 120 min of reperfusion. PC with the 5-min reperfusion markedly limited the infarct size after the 30-min ischemia (infarct size to area at risk (IS): 10% ± 3% vs 41% ± 3%, P 〈 0.05). PC was not protective when the reperfusion periods were 40 or 120 min (IS: 47% ± 5% and 44% ± 3%, P = not significant (NS) vs control, respectively). However, concomitant treatment with dilazep (0.2 mg/kg) preserved the PC effect in the 40-min reperfusion group (18% ± 5%, P 〈 0.05 vs control) but not in the 120-min reperfusion group (43% ± 4%, P = NS vs control). Protocol 2: Infarct was produced in a similar rabbit model by either a 45- or 50-min occlusion of a coronary artery and 2 days of reperfusion. PC was elicited by a preceding 5-min occlusion and a 5-min reperfusion. PC was protective in the 45-min occlusion group (30% ± 7% vs 67% ± 3%, P 〈 0.05) but not in the 50-min occlusion group (74% ± 4% vs 79% ± 5%, P = NS). Treatment with dilazep (0.2 mg/kg) failed to retrieve protection in this preconditioned group (77% ± 6%, P = NS vs 50-min occlusion group without PC). Thus, dilazep prolonged the infarct size-limiting effect of PC, but failed to retrieve protection in the group with a longer sustained ischemia.