Cream layer discoloration — yellow pigment producers: A yellow coloration in the creamy layer of milk is most commonly associated with which organism?

Introduction / Context:
Surface and cream layer color defects in milk arise from pigment-producing bacteria that contaminate equipment, tanks, or packaging environments. Identifying the typical pigment profile helps narrow the culprit organism.

Given Data / Assumptions:

• Defect: yellow color in the cream layer of milk.
• Candidate organisms include Pseudomonas synxantha (yellow) and P. syncyanea (blue).
• We must choose the most characteristic cause of yellow discoloration.

Concept / Approach:
Pseudomonas synxantha produces yellow pigments and is historically linked to yellow surface/cream layer defects in dairy. In contrast, P. syncyanea tends to yield blue pigments. Serratia marcescens is noted for red/pink (prodigiosin). Some Flavobacterium can be yellow, but the question emphasizes the classical pairing of defects with Pseudomonas species in milk handling environments.

Step-by-Step Solution:
Match defect color (yellow) with known pigment producers.Associate yellow with P. synxantha rather than blue-pigmented P. syncyanea.Select the single best classical answer.

Verification / Alternative check:
Dairy defect tables frequently list P. synxantha under yellow discolorations of cream or surface films.

Why Other Options Are Wrong:

• P. syncyanea: Blue pigmentation, not yellow.
• Both (a) and (b): Incorrect because the pigments differ in color.
• S. marcescens: Produces red/pink, not yellow.
• Flavobacterium spp.: Some are yellow but are less classically linked to the specific cream layer defect emphasized here.

Common Pitfalls:
Misattributing surface colors caused by mixed microbial communities; single-organism attribution assumes the dominant pigmented flora.

Final Answer:
Pseudomonas synxantha.