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Minimum Inhibitory Concentration and Postantibiotic Effect of Amikacin for Equine Isolates of Methicillin‐Resistant Staphylococcus aureus In Vitro
Author(s) -
CARON JOHN P.,
BOLIN CAROLE A.,
HAUPTMAN JOSEPH G.,
JOHNSTON KIMBERLY A.
Publication year - 2009
Publication title -
veterinary surgery
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 79
eISSN - 1532-950X
pISSN - 0161-3499
DOI - 10.1111/j.1532-950x.2009.00551.x
Subject(s) - amikacin , minimum inhibitory concentration , microbiology and biotechnology , staphylococcus aureus , medicine , methicillin resistant staphylococcus aureus , antibiotics , biology , bacteria , genetics
Objective— To report the minimum inhibitory concentration (MIC) of amikacin sulfate for equine clinical isolates of methicillin‐resistant Staphylococcus aureus (MRSA) and characterize the initial kill and duration of the postantibiotic effect (PAE) for selected strains. Study Design— Experimental study. Methods— Isolates of MRSA (n=35) had their amikacin MIC determined using the E‐test agar diffusion method. Two isolates with MICs>256 μg/mL limit were further characterized using broth macrodilution. Six distinct isolates with amikacin MICs of 32, 48, 128 (2 isolates) and 500 (2 isolates) μg/mL had PAE determinations made over a range of amikacin concentrations from 31.25–1000 μg/mL using standard culture‐based techniques. Results— Median MIC of the 35 isolates was 32 μg/mL (range 2 to >256 μg/mL). Mean PAE of selected MRSA strains had an overall mean (all amikacin doses) of 3.43 hours (range 0.10–9.57 hours). PAE for MRSA exposed to amikacin at 1000 μg/mL was 6.18 hours (range 3.30–9.57 hours), significantly longer than that for all other concentrations ( P <.0001). There was no statistically significant effect of isolate MIC on PAE. Conclusions— Isolates had a wide range of MIC; however, growth of all 6 selected strains were inhibited within the range of concentrations tested, including 2 strains with MICs of 500 μg/mL. PAE duration was not influenced by the MIC of amikacin but was significantly longer with treatment at 1000 μg/mL than at lower concentrations. Clinical Relevance— Clinical isolates of MRSA are susceptible to amikacin at concentrations achieved by regional perfusion: however, the modest duration of PAE observed suggest that further laboratory and in vivo evaluation be conducted before recommending the technique for clinical use.