Fluoroquinolone Therapy in Staphylococcus aureus Infections: Where Do We Stand?

The study aimed to evaluate the utility of various commonly used fluoroquinolones against Staphylococcus aureus isolates.

A total of 250 isolates of S. aureus were studied from different clinical specimens like blood, pus, wound swabs, sputum, ear swabs, and body fluids between November 2009 and December 2011. All the isolates were tested for their susceptibility to fluoroquinolones and other antimicrobial agents by Kirby-Bauer disc diffusion method using criteria of standard zone of inhibition. Methicillin-resistant S. aureus (MRSA) detection was done by cefoxitin disk diffusion method. The MRSA isolates were tested for minimum inhibitory concentration (MIC) to vancomycin by E-test strips. All the MRSA strains were sent to National Staphylococcal Phage-typing Centre, Maulana Azad Medical College, New Delhi for phage typing.

A total of 107 strains of S. aureus (42.8%) were detected as MRSA. Multidrug resistance was observed among the MRSA strains more commonly than among the MSSA stains. Among the fluoroquinolones, maximum resistance in MRSA was seen to ciprofloxacin (92.5%), followed by ofloxacin (80.4%). None of the S. aureus isolates showed resistance to vancomycin and linezolid. The MICs of vancomycin for the MRSA tested ranged from 0.5 to 2 μg/ml. Phage typing pattern of 107 MRSA isolates revealed that 37 (34.6%) MRSA isolates were nontypeable and 70 (65.4%) were typeable.

Ciprofloxacin can no longer be used in empirical therapy against MRSA infections. Use of other members of fluoroquinolone should be limited only to those strains that show laboratory confirmation of their susceptibility. Vancomycin remains the drug of choice to treat MRSA infections.