Simple and Fast Detection of Resistance to Antibiotic Inhibitors of Protein Synthesis in Gram-Negative Pathogens Through Evaluation of Mitomycin C-Induced Cell Elongation.

Increasing the resistance of Gram-negative pathogens to antibiotics that inhibit protein synthesis is of great concern. In life-threatening situations, an early detection of antibiotic resistance may improve patient outcome. A rapid assay for the identification of antibiotic resistance to gentamicin, tobramycin, and tigecycline has been designed and tested in clinical strains of Acinetobacter baumannii, Pseudomonas aeruginosa, and the Enterobacteriaceae Escherichia coli and Klebsiella pneumoniae. Exponentially growing cultures were incubated with 0.5 mg/L mitomycin C (MMC) for 2 hr (10 mg/L for A. baumannii), which induced significant cell enlargement as visualized under the microscope. Addition of the appropriate antibiotic dose 15 min before the addition of MMC prevented elongation when the strain was susceptible to the antibiotic, thereby inhibiting protein synthesis. Cell enlargement was not precluded in the antibiotic resistant strains, where protein synthesis had not been successfully inhibited. In comparison with the standard dilution-based antibiogram, the sensitivity of the assay was 100% and the specificity ranged between 96.0% and 100%. Results were obtained after 2 hr and 45 min from exponentially growing cultures. The procedure is easy, reliable, and demonstrates the suitability of the evaluation of simple morphological changes, which are protein synthesis dependent, for the rapid detection of antibiotic resistance.