A comparative study of M.I.C evaluator test with the broth microdilution method for antimicrobial susceptibility testing of Enterobacter cloacae isolated from cooked food.

Agar dilution and broth microdilution are widely recommended quantitative antimicrobial susceptibility test methods, but they are tedious and time consuming to implement as routine tests in many clinical laboratories. Therefore, this study aimed at comparing the broth microdilution and the M.I.C Evaluator method which has been validated for its high accuracy and easy performance for routine diagnostic use. Twenty Enterobacter cloacae strains were isolated following microbiological procedures and confirmation of the isolates used the API 20E test. The strains were evaluated for their susceptibility to seven antimicrobials using the broth microdilution and MIC Evaluator methods. The doubling dilution difference (essential agreement) in the MIC result was derived from: log2 (MIC by BMD) -log2 (MIC by M.I.C Evaluator method). The categorical agreement, interpreted as breakpoints of sensitive and resistance strains was also noted. Categorical agreement between M.I.C Evaluator strip and broth microdilution for amoxicillin, metronidazole and erythromycin was 100%: while categorical agreement for ciprofloxacin was 90%. The essential agreement for erythromycin, ciprofloxacin and tetracycline were 90%, 70% and 15% respectively. Results indicate a high efficiency of the M.I.C Evaluator strip method in determination of minimum inhibitory concentration as compared to broth microdilution method. However, further analysis regarding the suitability of the M.I.C Evaluator for testing Enterobacter cloacae is warranted considering that no consensus guidelines exist for the use of this method with the organism.