Timely identification of highly pathogenic bacteria is crucial for efficient mitigation of the connected harmful health effects. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) of intact cells enables fast identification of the microorganisms based on their mass spectrometry protein fingerprint profiles. However, the MALDI-TOF MS examination must be preceded by a time-demanding cultivation of the native bacteria to isolate representative cell samples to obtain indicative fingerprints. Isoelectric focusing (IEF) is capable of separating bacterial cells according to their isoelectric point while effectively removing other non-focusing compounds from sample matrix. In this work, we present a divergent-flow IEF chip (DF-IEF chip) fractionation as an alternative way for sample clean-up and concentration of bacterial cells to prepare samples usable for following MALDI-TOF MS analysis without the need of time-demanding cultivation. By means of DF-IEF chip method, we processed four species of highly pathogenic bacteria (Bacillus anthracis, Brucella abortus, Burkholderia mallei, and Yersinia pestis) inactivated with H