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J. M. Blondeau, C. Hesje; Impact of Benzalkonium Chloride (BAK) on the Mutant Prevention Concentrations (MPCs) of Gatifloxacin (Gfx) and Moxifloxacin (Mfx) Against Methicillin-Resistant Staphylococcus aureus (MRSA) Isolates. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1979. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the propensity of Gfx and Mfx to select for fluoroquinolone-resistant MRSA in the presence and absence of BAK. The MPC was defined as the antimicrobial drug concentration required to inhibit the growth of the least susceptible cell present in high-density bacterial populations.
Nine clinical MRSA isolates and 1 methicillin-susceptible S aureus strain, ATCC 29213, were tested. MRSA were inoculated at the density of 1010 CFU/mL onto agar plates containing 2-fold concentration increments of either Gfx or Mfx alone or in combination with BAK at concentrations of 5 µg/mL or 7-10 µg/mL. Following incubation under ambient conditions, the lowest concentration(s) preventing growth was determined as the MPC.
The MPCs of Gfx and Mfx in the presence and absence of BAK against MRSA isolates and ATCC 29213 are presented in the table. The presence of BAK at concentrations from 7 µg/mL to 10 µg/mL lowered the MPCs of Gfx and Mfx against MRSA by 32- to 1000-fold. The MPCs of Gfx and Mfx in the presence of 5 µg/mL of BAK were less consistent.
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