A Pink Milk Bottle Mystery.

The mother of a 5-week-old term infant brings the infant to the pediatrician’s office, along with a plastic milk bottle used to feed the baby. The bottle has splotches of red-pink material on the inside (Fig. 1). She wants to know what is happening to the milk in the bottle. The mother has been breastfeeding and has recently been transitioning to pumped breast milk in preparation for returning to work. For the past few days, she has noticed that the breast milk remaining in bottles that were left in a sink overnight after evening feedings turns bright pink by morning. The breast milk has been normal in color during pumping, in the pump tubing, and in bottles stored in the refrigerator before feedings. The mother denies taking any medications, herbal supplements, or illicit drugs while breastfeeding. The pregnancy was complicated by multiple urinary tract infections, which were treated with nitrofurantoin and trimethoprim-sulfamethoxazole. She denies any signs or symptoms of mastitis. The infant has been asymptomatic, feeding well, and is gaining weight. Birth was uncomplicated. The infant is afebrile and is well-nourished, well-hydrated, and in no distress. There are no lesions or abnormal findings on the oral mucosa. There is no lymphadenopathy. The remainder of the physical examination appears normal. The pediatrician sent samples of pink exudate in the bottle as well as stored, expressed breast milk (which had not yet been fed to the infant) for culture. Both cultures yielded the same microbe. What microbe is the most likely cause of this scenario? When the pediatrician calls to tell you this story and the culture results, what advice do you give? (See next page for discussion.) Figure 1. Infant bottle with pink material that developed after sitting at room temperature overnight after use for feeding of expressed breast milk. Pediatric ID Consultant