Emergence of phenotypic resistance to ciprofloxacin and levofloxacin in methicillin-resistant and methicillin-sensitive Staphylococcus aureus strains

• Published in: International journal of antimicrobial agents 2003-05, Vol.21 (5), p.420-424
• Main Authors: Limoncu, Mine Hosgör, Ermertcan, Safak, Çetin, Çigdem Banu, Cosar, Güner, Dinç, Gönül
• Format: Article
• Language: English
• Subjects: Antibacterial agents; Antibiotics. Antiinfectious agents. Antiparasitic agents; Biological and medical sciences; Ciprofloxacin; Ciprofloxacin - pharmacology; Drug Resistance, Multiple, Bacterial; Humans; Levofloxacin; Medical sciences; Methicillin - pharmacology; Methicillin Resistance; Microbial Sensitivity Tests; Ofloxacin - pharmacology; Pharmacology. Drug treatments; Phenotype; Phenotypic resistance; Serial Passage; Staphylococcus aureus; Staphylococcus aureus - drug effects
• ISSN: 0924-8579; 1872-7913
• DOI: 10.1016/S0924-8579(03)00006-2

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 4×MIC of levofloxacin after 48 h incubation, but 4 of 77 (5%) MSSA strains grew at the same concentration. At 4×MIC 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.