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Abstract
Objective:Acinetobacter baumannii species cause nosocomial infections and can subsequently develop multidrug resistance (MDR). The objective of this study was to evaluate the susceptibility of A. baumannii to a novel combination of colistin and tigecycline, which may provide a faster and more efficacious treatment via a synergistic effect.Methods:We included 50 MDR A. baumannii samples that were isolated in our clinics between 2009 and 2014. We used broth microdilution (BMD) and the E-test to evaluate the effects of colistin and tigecycline, and the E-test to assess the interaction of the colistin-tigecycline combination. The interaction between the two antibiotics was evaluated using the fractional inhibition concentration (FIC) index and was classified as follows: FIC≤0.5, synergistic; 0.5<FIC<1, partially synergistic; FIC=1, additive; 1<FIC<4, indifferent; and FIC≥4, antagonistic.Results:No tigecycline and colistin resistance was determined by BMD or E-test. The interaction between colistin and tigecycline, when used in combination, was 2% synergistic, 6% additive, 88% indifferent, and 4% antagonistic.Conclusion:Although combination therapy is suggested for MDR A. baumannii infections, our results suggest that the synergistic effect of the colistin-tigecycline combination is insufficient to make it an optimal treatment choice.
Highlights
Acinetobacter baumannii is one of the most common causes of bacterial nosocomial infections, especially in intensive care units and in immunocompromised patients; community-acquired Acinetobacter infections are rare
The MIC ranges of colistin in the A. baumannii serotypes were 0.03-1.0 μg/mL and 0.06-1.5 μg/mL according to broth microdilution (BMD) and E-test, respectively
The MIC ranges of tigecycline in the A. baumannii serotypes were 0.25-1.0 μg/mL and 0.03-1.25 μg/mL according to BMD and E-test, respectively (Fig.1)
Summary
Acinetobacter baumannii is one of the most common causes of bacterial nosocomial infections, especially in intensive care units and in immunocompromised patients; community-acquired Acinetobacter infections are rare. A. baumannii can cause various infections like nosocomial pneumonia, bacteraemia, meningitis, skin, soft tissue, and urinary tract infections.[1] The incidence of multidrug-resistant (MDR) Acinetobacter infections ranges between 47% and 93%, with mortality rates between 30% and 75%.2. Pak J Med Sci 2017 Vol 33 No 2 www.pjms.com.pk 393. Because of their ability to develop MDR and to survive on inorganic surfaces, Acinetobacter nosocomial infections are more detrimental to patients and challenging for clinicians. Because A. baumannii can develop resistance rapidly to various antibiotic classes, infections caused by these serotypes become pervasive, and the number of effective antibiotics available is limited. Because the search for novel antibiotics is challenging and has not proved as productive as expected, the effectiveness of some older antibiotics such as colistin has been evaluated in MDR microorganisms. A member of the polymyxin group of antibiotics, is an effective bactericidal antibiotic.[4]
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