Introduction: Current microbiological methods can only partly cover the requirements in speed and precision that are needed for timely and effective treatment of patients with infections. Improvement of infectious disease diagnostics is needed using fast, precise, inexpensive and culture-independent technologies. Raman spectroscopy is a fast, label free analytical technique that can also provide information on the biochemical composition of immune cells [1, 2].

Goal: We investigated whether Raman spectroscopy enables the differentiation of blood phagocytes that have engulfed methicillin-resistant (MRSA) and methicillin-susceptible (MSSA) Staphylococcus aureus strains. To limit genome-related variabilities, an isogenic strain pair was used.

Materials & Methods: Blood phagocytes were isolated from peripheral blood of 8 healthy donors and were incubated in the presence/absence of MRSA and MSSA at multiplicity of infection (MOI) 3. Neutrophils were incubated for 1 and 3 h and monocytes for 8 and 24 h. Raman imaging was applied onto 15 cells/treatment and data were analysed using Partial Least-Squares Discriminant Analysis (PLS-DA).

Results: Staphylococcus infected neutrophils could be discriminated form their naïve controls with 80% balanced accuracy (BA) after 1 h and 83.3% after 3 h, whereas monocytes with BA of 66.7% after 8 h that increased to 80% after 24 h. MRSA and MSSA infected neutrophils could not be discriminated in both time points (50% BA). In monocytes however, the BA of 50% obtained after 8h increased to 70% after 24 h.

Summary: The results of this first, prove-of-concept study show that Raman spectroscopy enables the discrimination of ex-vivo MRSA and MSSA phagocytosis by blood monocytes. This first step points towards a direction that is worth considering for further investigation and development, leading to better management of infectious diseases.

Financial support of the MCSA-COFUND Multiply Project (H2020 GA 713694) and the research campus InfectoGnostics (FKZ 13GW0096F) is gratefully acknowledged.

References

[1] Pistiki et al., Int. J. Mol. Sci. 2021, 22(19), 10481

[2] Ramoji A, et.al. Crit Care Explor. 2021;3(5): e0394-e