Emergence of phenotypic resistance to ciprofloxacin and levofloxacin in methicillin-resistant and methicillin-sensitive Staphylococcus aureus strains.
The emergence of phenotypic resistance to ciprofloxacin and levofloxacin in methicillin-sensitive and methicillin-resistant Staphylococcus aureus (MRSA) strains was studied. Twenty MRSA and 77 methicillin-sensitive S.aureus (MSSA) strains susceptible to both quinolones were investigated for resistance after single step or serial passages. No growth of 20 MRSA strains was observed at 4xMIC of levofloxacin after 48 h incubation, but 4 of 77 (5%) MSSA strains grew at the same concentration. At 4xMIC concentration of ciprofloxacin, 10 MSSA (13%) and five MRSA (25%) strains were grown. In the serial passages of MRSA strains, resistance to ciprofloxacin was 75 and 5% for levofloxacin by the third passage. In the seventh passage this resistance was 100 and 15%, respectively. In MSSA strains, resistance to ciprofloxacin was 75 and 19% to levofloxacin at the third passage and at the seventh passage, 100 and 61%, respectively. Emergence of ciprofloxacin resistance was more common and developed more rapidly than resistance to levofloxacin in both MRSA and MSSA strains.
Department of Pharmaceutical Microbiology, Faculty of Pharmacy, Ege University, 35100 Bornova, Izmir, Turkey. hosgorm@pharm.ege.edu.tr
Mine Hosgör
MH
Limoncu
Safak
S
Ermertcan
Cigdem Banu
CB
Cetin
Güner
G
Cosar
Gönül
G
Dinç
D002939:Ciprofloxacin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D006801:Humans; D064704:Levofloxacin; D008712:Methicillin / Q000494:pharmacology; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D015242:Ofloxacin / Q000494:pharmacology*; D010641:Phenotype; D012692:Serial Passage; D013211:Staphylococcus aureus / Q000187:drug effects*
D002939:Ciprofloxacin; D064704:Levofloxacin; D015242:Ofloxacin; D008712:Methicillin