Comparison of Colistin MIC by Microbroth Dilution, E-Test and Vitek-2, in Isolates of Acinetobacter spp. Isolated from Bloodstream Infections

Abstract

Background: Acinetobacter species are leading cause of nosocomial infections, causing significant morbidity and mortality globally including India. Being persistent in the hospital environment and rapidly developing resistance to a wide variety of antibiotics are the most important features of this pathogen. The present study aimed to compare Colistin MIC of Acinetobacter species isolated from the blood samples by E test and Vitek 2 to the standard broth micro dilution test. Methodology: Two antibiotic susceptibility test methods, The Vitek-2 and the E test, against the reference broth micro dilution method in terms of the various parameters such as Reproducibility, reliability, cost and time effectiveness. Data obtained from the current study regarding antimicrobial resistance of Acinetobacter species recovered from clinical specimens referred to microbiology laboratory of SKIMS and was analyzed by using SPSS20.0. Results: Out of 100 isolates of Acinetobacter species analyzed from blood specimens the distribution of Acinetobacter species according to different clinical diagnosis of patients 89% were A. baumannii and 11% were A. lwoffii. Seventy three percent of them were from males and 27% of them were from females with a mean age of 39.6 (SD±27.46). Regarding the specimen and isolate sources, the majority were from ICU (54%), Surgical ward (26%), Medical ward (16%) and 4% from Outpatient department of SKIMS. Significant descending trends of antimicrobial resistance was shown for Amoxicillin/Clavulanic acid, Cefoperazone/ Sulbactam combination, Cotrimoxazole (100%), Levofloxacin (92%) Piperacillin/Tazobactam, Ciprofloxacin (90%), Cephalosporins (>80%), Imipenem and Meropenem (76%), Amikacin (68%), Gentamycin (67%), Tigecycline (11%) and 0% for Colistin respectively. Conclusion: from the study it could be concluded that the best reference method for testing susceptibility to the Polymyxins still remains to be defined. However, in routine clinical practice in most regions worldwide, where a reference method can hardly be implemented, the interpretation of Colistin susceptibility should preferably be based on results of automated systems such as Vitek-2 or the E test. The micro broth Dilution method remains the most reliable and reproducible, however most tedious and time-consuming method. Colistin remains a very effective, least resisted drug for MDR Acinetobacter species as compared by all the three methods. Keywords: Acinetobacter species; Antimicrobial resistance; Colistin; E test and Vitek 2.