Egg spoilage — ‘‘Black rot’’ of eggs: Which microorganisms are most commonly responsible for this black discoloration defect during storage?

Introduction / Context:
Egg spoilage manifests in named defects such as ‘‘black rot,’’ ‘‘green rot,’’ and ‘‘red rot.’’ Recognizing the typical causative agents helps in quality control and storage decisions across the egg supply chain.

Given Data / Assumptions:

• Defect: black rot of eggs (blackened contents and strong off-odors).
• Environment: storage with potential contamination through shell pores or cracks.
• Candidate organisms include Proteus, Micrococcus/Bacillus, and fungi.

Concept / Approach:
Black rot is closely associated with Proteus spp., which generate hydrogen sulfide. H2S reacts with iron compounds in the yolk to form iron sulfide, producing characteristic dark to black discoloration and putrid odor.

Step-by-Step Solution:
Identify signature metabolite: H2S from Proteus during protein breakdown. Explain discoloration: H2S + Fe → FeS (black), especially in yolk region. Match classic pairing: black rot ↔ Proteus spp. Choose ‘‘Species of Proteus.’’

Verification / Alternative check:
Diverse egg-spoilage charts consistently assign black rot to Proteus; other organisms cause different color/texture changes.

Why Other Options Are Wrong:

• Micrococcus/Bacillus: more often general spoilage, ropiness, or surface growth rather than black rot.
• Molds/yeasts: cause mustiness, visible mycelia, or fermentative off-flavors, not black rot.
• All of these: too broad; the most common cause is Proteus.

Common Pitfalls:
Attributing all dark egg defects to fungal growth; ignoring the H2S–iron chemistry underlying the black color.

Final Answer:
Species of Proteus