In vitro Susceptibilities of Methicillin-Susceptible and Resistant Staphylococci to Traditional Antibiotics Compared to a Novel Fluoroquinolone

Abstract

Background: To assess the in-vitro efficacy of delafloxacin, a new fourth generation fluoroquinolone, against Staphylococcus vitreous isolates from patients with clinically diagnosed endophthalmitis. This is the first investigation of delafloxacin in ocular tissues. Methods: Intravitreal isolates of culture-proven S. aureus and S. epidermidis were identified between 2014 and 2018. Minimum inhibitor concentrations (MIC) were determined using ETEST strips. The antibiotic susceptibilities were tested against a panel of drugs including glycopeptides such as vancomycin, as well as traditional and newer fluoroquinolones (levofloxacin, moxifloxacin, and delafloxacin). Results: Of 45 total isolates identified between 2014 and 2018, 13% (6) were methicillin-resistant S. aureus (MRSA), 9% (4) were methicillin-sensitive S. aureus (MSSA), 53% (24) were methicillin-resistant S. epidermidis (MRSE), and 24% (11) were methicillin-sensitive S. epidermidis (MSSE). Among the fluoroquinolones, resistance rates were 61% for levofloxacin, 50% for moxifloxacin, and 12% for delafloxacin. Inter-class comparisons between delafloxacin and the two other fluoroquinolones demonstrated higher Gram-positive susceptibility to delafloxacin (p < 0.01). MIC90 values were lowest for delafloxacin (1.0 μg/mL) compared to levofloxacin (8.0 μg/mL) and moxifloxacin (8.0 μg/mL). Vancomycin was 100% effective against all isolates with MIC90 value of 0.75 μg/mL. Conclusion: Compared to levofloxacin and moxifloxacin, the newer fluoroquinolone delafloxacin demonstrated the lowest MICs values and lowest rates of resistance for Gram-positive in-vitro S. epidermidis and S. aureus vitreous isolates.

Potential new fluoroquinolone treatments for suspected bacterial keratitis

“… 65 In a recent in vitro study comparing delafloxacin to levofloxacin, moxifloxacin and vancomycin against bacterial isolates from cases of endophthalmitis, delafloxacin showed significantly lower rates of resistance to S. epidermidis and S. aureus, including methicillin-resistant isolates, with low MICs. 66 Direct comparison with moxifloxacin across all the Staphylococcus isolates from this study demonstrated significantly increased susceptibility to delafloxacin. Delafloxacin has low (16%) protein binding, suggesting that its activity may not be significantly reduced in the inflamed cornea.…”

“…Similar to the fourth generation FQs, delafloxacin is active against both bacterial gyrase and topoisomerase IV, reducing the risk of AMR 65. In a recent in vitro study comparing delafloxacin to levofloxacin, moxifloxacin and vancomycin against bacterial isolates from cases of endophthalmitis, delafloxacin showed significantly lower rates of resistance to S. epidermidis and S. aureus, including methicillin-resistant isolates, with low MICs 66. Direct comparison with moxifloxacin across all the Staphylococcus isolates from this study demonstrated significantly increased susceptibility to delafloxacin.…”

Emerging Antibiotic Resistance Patterns Affect Visual Outcome Treating Acute Endophthalmitis

“…Increasing rates of resistance have been reported [21][22][23], and in this study, we showed 16.7% resistance across all isolates. Fourthgeneration fluoroquinolones, such as delafloxacin, demonstrate promising MIC effects in in-vitro studies and may be considered as adjunctive treatment in the future [24]. Some ophthalmologists use early systemic corticosteroids [1,13], with others concerned with inducing an immunosuppressive state.…”

Characterization of Pseudomonas aeruginosa isolates from patients with endophthalmitis using conventional microbiologic techniques and whole genome sequencing

“…All isolates were sensitive to ceftazidime, which is generally used as a first line intravitreal antibiotic along with vancomycin at this institution. Interestingly, isolates were pan-sensitive to fluoroquinolones tested, including delafloxacin, a newly registered fluoroquinolone not currently used in the treatment of ocular infections [ 22 ]. This resistance profile suggests there may be significant geographic variation, which may be better studied in larger cohorts.…”