Erbil Polytechnic University


A new method developed for in-vitro susceptibility test in medical laboratories consist of micro tubes or gloves containing dehydrated tryptic soya broth, 5% glucose, 0.1% bromothymol blue and one type of antibiotics (ampicillin, tetracycline and chloramphenicol) with critical concentration MIC (minimum inhibitory concentration) for susceptibility. Standard quality control
strains of bacterial (Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa) suspension were adjusted to 0.5 McFarland turbidity standard (1 × 106 cell/mL) were used in inoculation the media and incubated two hours at 37 °C. The MIC of ampicillin against E. coli, S. aureus, and P. aeruginosa were 4, 32, and 256 µg/mL of the media for the bacteria respectively, while the MIC of tetracycline against bacteria were 512, 512 and 32 µg/mL respectively, the MIC of chloramphenicol were 512, 32 and 512 µg/mL, respectively. Where, the resistant bacteria to the antibiotics could grow and ferment glucose sugar producing a color change of the media from blue to yellow, while the sensitive bacteria do not grow or show no change in color. Our study result compared with common used antibiotic disk method obtaining similar results. This developed method characterized by fast (only two hours) and less cost in comparison to conventional technique. The new micro tube strip is highly stable (more than one year) with more sensitive in detection of variable pathogenic bacteria including standard bacteria strains compared with conventional technique..