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Due to the current relevance of antibiotic resistances and the associated growing challenge of therapy limitations in everyday clinical practice, the development of rapid and cost-effective resistance tests is increasingly becoming the focus of research interest.
The work presented here investigates the development of a method to quickly and reliably determine the resistance of bacteria to antibiotics by analyzing and evaluating the spectra after MALDI-TOF measurement of the incubated isolates with or without added antibiotics.
The basic idea was whether the presence of resistance of a certain isolate can be detected very early in a mass spectrum under the influence of the antibiotic. For this purpose, bacteria were incubated with and without an antibiotic for a short time (3-4 hours) and then a spectrum was generated using MALDI-TOF measurement. The hypothesis was that inhibition of growth, killing or the beginning of growth could be detected very early in a mass spectrum.
The experiments were carried out with two clinically relevant bacteria (E. coli and P. mirabilis). In preliminary experiments it was analysed how the amount of bacteria, antibiotic concentration, incubation time and other conditions affected the spectra. It was shown that differences at specific peaks (9700 for E. coli and 8370 for P. mirabilis) could be used as surrogate markers for resistance or susceptibility for antibiotics in bacteria. The results were compared with the reference methods of resistance testing (E-Test and MicroScan® Walkaway) and showed equal findings.
Depending on the bacteria examined, reliable information on the efficacy of the antibiotic could be obtained after only three or four hours of incubation. As a result of this work it is clear that MALDI-TOF is a reliable and rapid method for detecting resistance, at least for the combinations of germs and antibiotics investigated in this work.
Further experiments must now show whether the method developed here can be used for other bacteria and whether it is suitable for routine application.