Rapid Assessment of Resistance to Antibiotic Inhibitors of Protein Synthesis in the Gram-Positive Pathogens,Enterococcus faecalisandStreptococcus pneumoniae, Based on Evaluation of the Lytic Response

Phenotypic antibiotic susceptibility testing of pathogenic bacteria using photonic readout methods: recent achievements and impact

The development of antibiotic resistances in common pathogens is an increasing challenge for therapy of infections and especially severe complications like sepsis. To prevent administration of broad-spectrum and potentially non-effective antibiotics, the susceptibility spectrum of the pathogens underlying the infection has to be determined. Current phenotypic standard methods for antibiotic susceptibility testing (AST) require the isolation of pathogens from the patient and the subsequent culturing in the presence of antibiotics leading to results only after 24-72 h. Since the early initialization of an effective antibiotic therapy is crucial for positive treatment result in severe infections, faster methods of AST are urgently needed. A large number of different assay systems are currently tested for their practicability for fast detection of antibiotic resistance profiles. They can be divided into genotypic ones which detect the presence of certain genes or gene products associated with resistances and phenotypic assays which determine the effect of antibiotics on the pathogens. In this mini-review, we summarize current developments in fast phenotypic tests that use photonic approaches and critically discuss their status. We further outline steps that are required to bring these assays into clinical practice.

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.