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In vitro activity of antibiotic combinations against multidrug‐resistant strains of A cinetobacter baumannii and the effects of their antibiotic resistance determinants
Author(s) -
Miyasaki Yoko,
Morgan Margie A.,
Chan Raymond C.,
Nichols W. Stephen,
Hujer Kristine M.,
Bonomo Robert A.,
Murthy A. Rekha
Publication year - 2012
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.2011.02480.x
Subject(s) - acinetobacter baumannii , antibiotics , microbiology and biotechnology , colistin , biology , antibiotic resistance , multiple drug resistance , bacteria , genetics , pseudomonas aeruginosa
Various combinations of antibiotics are reported to show synergy in treating nosocomial infections with multidrug‐resistant ( MDR ) A cinetobacter baumannii ( A . baumannii ). Here, we studied hospital‐acquired outbreak strains of MDR A . baumannii to evaluate optimal combinations of antibiotics. One hundred and twenty‐one strains were grouped into one major and one minor clonal group based on repetitive PCR amplification. Twenty representative strains were tested for antibiotic synergy using E test ® . Five strains were further analyzed by analytical isoelectric focusing and PCR to identify β‐lactamase genes or other antibiotic resistance determinants. Our investigation showed that the outbreak strains of MDR A . baumannii belonged to two dominant clones. A combination of colistin and doxycycline showed the best result, being additive or synergistic against 70% of tested strains. Antibiotic additivity was observed more frequently than synergy. Strains possessing the same clonality did not necessarily demonstrate the same response to antibiotic combinations in vitro . We conclude that the effect of antibiotic combinations on our outbreak strains of MDR A . baumannii seemed strain‐specific. The bacterial response to antibiotic combinations is probably a result of complex interactions between multiple concomitant antibiotic resistance determinants in each strain.

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