Investigation of in-vitro susceptibility of multidrug-resistant Acinetobacter baumannii strains isolated from clinical specimens to tigecycline

Abstract

The management of infections due to A. baumannii is difficult because of rapidly developing resistance, however, tigecycline, a glycylcycline antimicrobial, is in use for several years. In the present study, it was aimed to determine the susceptibility rates of A. baumannii to tigecycline. A total of 90 A. baumanni isolates were tested using three methods such as disk diffusion, broth microdilution, and E-test. The MIC50 and MIC90 values and the MIC range were found as 2 µg/ml, 4 µg/ml, and 0.1-8 µg/ml by microdilution; and 2 µg/ml, 6 µg/ml, and 0.1-12 µg/ml by E-test, respectively. There were a few major errors as well as the minor rates were all high as between 35.7%-46.7%. The accuracy rates between the methods were low as 53.3% (48/90) between disk diffusion and E-test, 51.1% (46/90) between disk diffusion and microdilution, and 60.0% (54/90) between E-test and microdilution. In the ROC curve analysis, an inhibition zone diameter of susceptibility breakpoint of 21.5 mm had sensitivity between 68.8%-88.9%; specificity between 81.9%-87.9%; and accuracy between 80.0%-83.33%. An analysis based on EUCAST's non-species breakpoints, the MIC tests showed higher accuracy with a rate of 96.7%, however, performance of disk diffusion got worse as lower than 25%. In conclusion, we showed that the reliability of the methods even did not remain as high as the past. Our study presented that none of three methods revealed reliable results in determination of susceptibility of A. baumanni to tigecycline, so the clinical response should be followed up carefully in such cases.

Tigecycline susceptibility of multidrug-resistant Acinetobacter baumannii from intensive care units in the western Balkans

“…The MIC 50 and MIC 90 values were found to be 16 and 32 mg/mL, respectively, with a wide range of 1.0-128 mg/mL [25]. obtained in the present study [26]. Likewise, discrepant MIC values of TGC obtained by gradient strip test and BMD have been reported [27].…”

Active efflux pump adeB is involved in multidrug resistance of Acinetobacter baumannii induced by antibacterial agents

“…Crude mortality rate and attributable mortality of the infection were reported to be 52 and 10-35%, respectively (4). Multidrug-resistant A. baumannii is considered as a leading cause of nosocomial infection, particularly in critically ill patients (5). A. baumannii has been reported to be resistant to a broad range of antimicrobial agents, and the tendency for its epidemic spread has subsequently extended (6).…”

Susceptibility to tigecycline of Acinetobacter baumannii strains isolated from intensive care unit patients

“…However, Piewngam and Kiratisin [11] suggest that the MIC breakpoint should be modified to S ≤ 0.5 and R > 2 mg L -1 . It has been pointed out that the determination of the antimicrobial activity of tigecycline might vary with the use of different methods, while the disk diffusion method is not reliable as regards the determination of susceptibility to tigecycline and gives lower susceptibility rates as compared to Etest or the broth microdilution method (BMD) [10,12]. Zarkotou et al [13] compared the broth microdilution method with VITEK2, Etest and MIC test strips.…”

“…On the other hand, there are some publications which present the opposite conclusions. Draghi et al [12,14]. As shown above, there is a great problem with obtaining reliable results of Acinetobacter susceptibility testing to tigecycline as there are no standardized guidelines, while the results from many studies have been inconclusive.…”