Imaging flow cytometry-based analysis of bacterial profiles in milk samples

Imaging flow cytometry (IFC) combines microscopy-based capturing of cell images with conventional flow cytometry-based high-throughput analysis. Thus, IFC approach may limit false-positive results and provide more accurate and unambiguous data. This may be particularly important in the case of the single-cell analysis of relatively small biological objects such as bacteria. The microbial quality control of milk samples is of a special interest during milk processing and several methods have been previously developed to address the presence of bacterial species in milk and other economically important dairy products. However, the vast majority of screening assays is time-consuming and cost-ineffective to be used as a routine test. In the present study, we propose combined acridine orange (AO) staining and IFC-based profiling of microbial species as a novel alternative method for the microbial quality control of milk samples. Eight bacterial profiles (Lactococcus lactis, Lactobacillus rhamnosus GG, Bacillus subtilis, Bacillus cereus, Bacillus megaterium, Staphylococcus aureus, Salmonella typhimurium and Sarcina lutea) were characterized using a number of IFC parameters and IFC approach was also validated using commercially available milk samples and probiotic supplement. The obtained results suggest that IFC-based microbial profiling may be considered as a potentially useful method for rapid screening for selected bacterial species in milk samples.