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Item Evaluation of a Commercial Broth Microdilution Panel for Colistin Susceptibility Testing of Clinical Isolates of Escherichia coli and Klebsiella pneumoniae(2021) Mirza, Hasan C.; Bicakcigil, Asiye; Liste, Umran; Sancak, Banu; 0000-0002-8853-3893; 33978373; F-1232-2015Background: Colistin is among the last resort antibiotics for the treatment of infections caused by multidrug-resistant Gram-negative pathogens. Antimicrobial susceptibility testing of colistin is challenging due to its physicochemical properties. Broth microdilution (BMD) is the recommended method for colistin susceptibility testing. However BMD is not practical for clinical microbiology laboratories as manual preparation of BMD plates is time-consuming and labor intensive. Recently, some more user-friendly BMD products with commercial panels have become available. Our objective was to evaluate the performance of a commercial broth microdilution (BMD) product [Sensititre (Thermo Fisher Scientific)] for colistin MIC determination by comparison with reference BMD method using a collection of E. coli and K. pneumoniae isolates. Methods: A total of 323 unique patient isolates (102 E. coli, 221 K. pneumoniae) were included in the study. Isolates were stored at -70 degrees C and subcultured twice on sheep blood agar before testing. Colistin MICs of the isolates were determined using Sensititre (a premade BMD product with dried antibiotics) and an 'in-house prepared BMD panel prepared in accordance with CLSI guidelines' (reference method). MIC determination with Sensititre was performed according to manufacturer's instructions. The reference method was performed using untreated 96-well sterile polystyrene plates. Colistin MIC results were interpreted according to EUCAST breakpoints (susceptible, <= 2 mg/L; resistant, > 2 mg/L). Results: Overall susceptibility rate of isolates to colistin by reference BMD was 75.9%. Overall categorical agreement (CA), essential agreement (EA), very major error (VME), and major error (ME) rates for Sensititre were 98.5%, 72.5%, 3.8%, and 0.8%, respectively. The CA and EA between Sensititre and reference BMD for the isolates with reference colistin MICs close to the susceptibility breakpoint (2 - 8 mg/L) was 94.2% and 48.1%, respectively. Sensititre yielded a VME rate of 15% and ME rate of 0%, respectively, for this subset of isolates. Conclusions: In conclusion, Sensititre showed high CA but low EA with reference BMD for entire collection of isolates. The VME rate was just slightly above 3% and ME rate was acceptable. The rates of CA and EA were decreased and the rate of VME was increased when a subset consisting of more challenging isolates was used.Item In Vitro Susceptibility of Tigecycline and Colistin Against Stenotrophomonas maltophilia(2018) Turan Özden, Hale; Togan, Turhan; Azap, ÖzlemIntroduction: Gram-negative bacillus Stenotrophomonas maltophilia is resistant to drugs (multi-drug resistance-MDR) and it can be isolated from nature. Treatment of the infections resulting from S. maltophilia could be problematic due to multi-resistance. Materials and Methods: 72 S. maltophilia strains isolated from clinical samples were included into the study. Sensitivity was determined using Tigecycline and Colistin E-test MIC method performed in the Clinical Microbiology laboratory of Baskent University, Medical Faculty between 2010 and 2014. Results: In our study, colistin MIC range was found as 0.016-8 mg/L. MIC50 and MIC90 values were determined respectively as 1.5 mg/L and 12 mg/L. Tigecycline MIC range was 0-96 mg/L, and MIC50 was 0.19 mg/L and MIC90 was 1.5 mg/L. Furthermore, one tigecycline resistant strain was detected. Conclusion: We believe that the determination of novel treatments and protocols and their standardization using multidisciplinary approaches can facilitate to cope with problematic and resistant nosocomial infections developed by S. maltophilia.