In vitro Activity of Delafloxacin against Methicillin-Resistant Staphylococcus aureus Isolated from Various Clinical Specimens

Abstract

Introduction: Delafloxacin is a novel fluoroquinolone which has anionic and weak acid character at neutral pH. Activity of delafloxacin is reported to be increased in acidic environments. Many infections are characterized by acidic pH. Staphylococcus aureus is a microorganism which can survive and multiply in mildly acidic environments. The aim of this study was to compare the activity of delafloxacin and other fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin) against MRSA isolates at neutral (7.4) and acidic (5.5) pH.

Materials and Methods: A total of 51 MRSA isolated from various clinical specimens were included in the study. Disk diffusion method was used for antimicrobial susceptibility testing. The pH of Mueller Hinton Agar was adjusted to 7.4 or 5.5, and used as the medium for antimicrobial susceptibility testing. EUCAST breakpoints were used for ciprofloxacin, levofloxacin and moxifloxacin. FDA breakpoints were used for delafloxacin.

Results: The most active fluoroquinolones against MRSA isolates at neutral pH were delafloxacin and moxifloxacin. Delafloxacin and moxifloxacin susceptibility rates of isolates were same (82.4%) at neutral pH. Of the isolates, 9.8% and 17.6% were resistant to delafloxacin and moxifloxacin, respectively. Four moxifloxacin-resistant isolates were categorized as intermediate to delafloxacin. Of the isolates, 76.5% and 78.4% were 'I - susceptible, increased exposure' to ciprofloxacin and levofloxacin, respectively. Of the isolates, 23.5% and 21.6% were resistant to ciprofloxacin and levofloxacin, respectively. At acidic pH; ciprofloxacin, levofloxacin and moxifloxacin susceptibility rates of isolates were not changed. However, all delafloxacin resistant/intermediate isolates at neutral pH became susceptible to delafloxacin at acidic pH.

Conclusion: Delafloxacin was the most active fluoroquinolone against MRSA isolates at acidic pH. Based on our findings, delafloxacin may represent a treatment option for MRSA infections characterized by low pH.