Growth of Selected Bacteria in Processed Human Milks ¹

Area of Science:

• Microbiology
• Food Science
• Public Health

Background:

• Human milk is a vital source of nutrition for infants.
• The microbial composition of human milk can be affected by processing and storage.
• Understanding bacterial survival in human milk is crucial for infant health.

Purpose of the Study:

• To investigate the survival and growth of common bacteria in human skim milk under various processing conditions.
• To determine the impact of freezing, pasteurization, and heat sterilization on bacterial viability.

Main Methods:

• Bacterial cultures of Pseudomonas fluorescens, Micrococcus luteus, Micrococcus sp. 102, and Staphylococcus aureus were inoculated into pooled human skim milk.
• Milk samples were subjected to different treatments: raw, frozen, pasteurized, and heat-sterilized.
• Bacterial counts were monitored over time at incubation temperatures of 25°C and 37°C.

Main Results:

• Pseudomonas fluorescens grew robustly in all milk types.
• Staphylococcus aureus showed significant growth in raw, pasteurized, and frozen milk.
• Micrococcus sp. 102 survival varied, with limited recovery in raw and frozen milk but growth in sterilized milk.
• Micrococcus luteus demonstrated poor survival, with only transient recovery in heat-sterilized milk.

Conclusions:

• Bacterial survival and growth in human skim milk are highly dependent on the bacterial species and milk processing method.
• Heat sterilization appears to be the most effective method for reducing bacterial load, though some species can still grow.
• Further research is needed to optimize milk processing to ensure infant safety.