MALDI-MS Proteotyping of Cutibacterium Acnes

Significance of the topic

MALDI-TOF–based proteotyping of Cutibacterium acnes enables rapid subspecies and subtype identification critical for dermatological research, clinical microbiology, and quality control in industrial settings.

Objectives and study overview

This study aimed to classify 24 C. acnes strains at both subspecies (types I, II, III) and subtype (IA1, IA2, IB) levels using MALDI-MS proteotyping combined with eMSTAT Solution™ and Strain Solution™ software. It sought to overcome the ambiguity of conventional fingerprinting and reduce reliance on DNA‐based methods like MLST.

Methodology and instrumentation

• Database construction: Theoretical masses of ribosomal proteins (RPs) were calculated from six genome‐sequenced reference strains, accounting for possible N‐terminal methionine loss.
• Mass spectrometry: AXIMA Performance™ MALDI-TOF MS in positive‐ion linear mode (m/z 2,000–30,000) with sinapinic acid matrix (10 mg/mL in 50 % acetonitrile/1 % TFA) and methylenediphosphonic acid as additive.
• Sample preparation: Bacterial cell lysis via zirconia bead grinding, centrifugation, ultrafiltration of protein fractions, mixing with matrix solution, and spotting on target plate.
• Data analysis: Peak matching within ±200 ppm using eMSTAT Solution; cluster analysis by UPGMA on binary biomarker presence/absence table in Strain Solution.

Main results and discussion

• Detected 31 ribosomal proteins in reference strain JCM 6425T, of which 10 stable RPs served as species- or subtype‐specific biomarkers.
• Six common RPs (L9, L29, L30, S8, S15, S19) enabled unequivocal species identification.
• Four additional RPs, including an antitoxin at m/z ~7035, discriminated subtypes IA1 (peak present) versus IA2 (absent) with perfect reproducibility.
• CsbD-like protein peaks around m/z 7200 further distinguished other subtypes (IB, II, III).
• Cluster analysis correctly grouped all 24 strains into three major clusters (types I, II, III) and resolved subclusters IA1, IA2, IB within type I.

Benefits and practical applications

• Delivers a rapid, cost‐effective proteomic workflow for strain typing without DNA extraction or sequencing.
• Complements or replaces MLST in routine laboratories for epidemiological tracking and microbiome profiling.
• Facilitates high‐throughput screening in industrial QC, dermatological research, and clinical diagnostics.

Future trends and potential applications

• Expansion of biomarker libraries to cover diverse bacterial species and clinical isolates.
• Integration with machine learning and automated software for real‐time identification.
• Optimization of sample prep and instrumentation for increased sensitivity and throughput.
• Development of standardized proteotyping databases for global inter‐laboratory comparability.

Conclusion

MALDI-MS proteotyping using assigned ribosomal proteins and antitoxin biomarkers provides a robust, non‐DNA‐based approach for discriminating C. acnes phylotypes. This workflow offers speed, accuracy, and scalability, positioning it as a valuable tool alongside established molecular techniques.

Instrumentation used

• AXIMA Performance™ MALDI-TOF MS (Shimadzu)
• Sinapinic acid matrix solution with methylenediphosphonic acid additive
• eMSTAT Solution™ and Strain Solution™ software for peak analysis and clustering

References

1. Teramoto K, et al. MALDI-MS proteotyping of Cutibacterium acnes. Proc. Jpn. Acad., Ser. B. 2019;95:612–623.
2. Nagy E, et al. Mass spectrometric fingerprinting of C. acnes subtypes. Anaerobe. 2013;20:20–26.
3. Dekio I, et al. Phylotyping of C. acnes by MLST and mass spectrometry. J Med Microbiol. 2012;61:622–630.