Volatile Characterization of American Foulbrood Disease Using Comprehensive Two-Dimensional Gas Chromatography

Significance of the Topic

American foulbrood (AFB) is a devastating bacterial disease of honey bee brood caused by Paenibacillus larvae spores. Its rapid spread and persistent spores necessitate sensitive detection methods and effective yet non‐destructive sterilization strategies to protect apiaries and maintain pollinator health.

Objectives and Study Overview

This study aimed to apply comprehensive two‐dimensional gas chromatography with time‐of‐flight mass spectrometry (GC×GC‐TOFMS) to characterize volatile profiles associated with AFB at various infection stages and to assess the impact of gamma irradiation as a sterilization treatment on these volatiles.

Methodology and Instrumentation

• Sample types: blank vials, healthy comb material, aged diseased scales, fresh diseased scales, and gamma‐irradiated diseased scales stored in headspace vials at –20 °C.
• Headspace sampling: solid‐phase microextraction (SPME) using LPAL‐3 device (CTC Analytics), no further sample preparation.
• Chromatographic system: Pegasus BT4D GC×GC‐TOFMS (LECO Corporation).
• Columns: first‐dimension HP‐5Q (29.3 m × 250 µm ID × 0.25 µm df); second‐dimension DB‐17MS (0.975 m × 250 µm ID × 0.25 µm df).
• Modulation: quad‐jet dual‐stage cryogenic modulator, 3.0 s period (0.60 s hot pulse, 0.40 s cold pulse).
• Oven program: 40 °C hold 3 min, ramp to 240 °C at 8 °C/min (hold 1 min); secondary oven +5 °C offset; modulator +15 °C offset.
• Carrier gas: hydrogen at 1.25 mL/min; inlet split flow 62.5 mL/min at 250 °C.
• TOFMS parameters: ion source 250 °C; mass range 29–500 amu; acquisition rate 200 spectra/s.
• Data processing: ChromaTOF software with minimum signal‐to‐noise ratio of 200 and minimum stick count of 3; tentative identifications based on mass spectral libraries.

Main Results and Discussion

Total ion chromatograms revealed distinct volatile intensities for each sample type. Healthy comb exhibited the lowest overall response, while gamma‐irradiated scales showed the highest intensity of volatiles. Key compounds tentatively identified included 2,3‐butanediol, 2‐methylpropanoic acid, benzene, and 1,4‐dichlorobenzene. The presence and abundance of these markers correlated with infection stage and irradiation treatment, indicating that gamma irradiation alters the volatile profile but does not fully eliminate all compounds.

Benefits and Practical Applications

• Rapid profiling of AFB‐related volatiles supports the training and deployment of scent‐detection dogs for early disease detection in hives.
• GC×GC‐TOFMS provides high‐resolution separation and sensitive identification of infection‐specific markers.
• Monitoring volatile changes after gamma irradiation offers a non‐destructive method to evaluate sterilization efficacy and hive decontamination protocols.

Future Trends and Applications

• Identification and validation of AFB‐specific volatile biomarkers to improve diagnostic selectivity and sensitivity.
• Integration of chemometric and machine learning algorithms for automated pattern recognition and predictive diagnostics.
• Optimization of gamma irradiation doses to balance microbial sterilization with minimal alteration of apiary components.
• Development of portable GC×GC or alternative sensor platforms for in‐field AFB screening.

Conclusion

GC×GC‐TOFMS has demonstrated the capability to differentiate volatile signatures of honey bee materials at various AFB infection stages and to assess the impact of gamma irradiation on these profiles. The approach offers a powerful tool for early disease detection, non‐destructive sterilization monitoring, and the development of advanced diagnostic methods.

References

1. Liolios V, Kanelis D, Tananaki C, Rodopoulou MA. A comparative study of healthy and American foulbrood‐infected bee brood (Apis mellifera L.) through the investigation of volatile compounds. Agriculture. 2022;12(6):812.
2. Genersch E. American Foulbrood in honeybees and its causative agent, Paenibacillus larvae. Journal of Invertebrate Pathology. 2010;103(Suppl 1):S10–S19.
3. Genersch E. Paenibacillus larvae and American foulbrood – long since known and still surprising. Journal für Verbraucherschutz und Lebensmittelsicherheit. 2008;3(4):429–434.