Inactivation behaviors of selected bacteria in ultraviolet-C-treated human breast milk

- Test organisms exhibited varying inactivation patterns.
- Total sublethal injury was observed in S. aureus in breast milk.
- The greatest population reduction was observed in Salmonella.
- The least population reduction was observed in S. aureus.

This study determined the inactivation behaviors, which include inactivation pattern, sublethal injury development, and inactivation kinetic parameters of selected bacteria in UV-C treated human breast milk. Multi strain mixtures of Salmonella enterica, Escherichia coli O157:H7, non-pathogenic E. coli, Pseudomonas aeruginosa, Listeria monocytogenes, and a lone strain of Staphylococcus aureus were inoculated into donated breast milk prior to UV-C inactivation studies. Results showed that the test organisms exhibited two types of inactivation patterns, making it difficult to directly compare UV-C resistance. S. enterica and non-pathogenic E. coli exhibited a monophasic log-linear inactivation pattern within the 60-min UV-C treatment period. All other challenge organisms exhibited a biphasic inactivation pattern characterized by a faster initial log linear inactivation, followed by a slower inactivation tailing. Sublethal injury rates were small in all test organisms except for S. aureus, which developed total sublethal injury throughout the UV-C exposure. Despite the injury rates, S. aureus had the least total population reduction (2.63 log CFU) after the 60-min treatment, while S. enterica had the greatest reduction (3.88 log CFU). The inactivation behaviors established in this work provide baseline information in the development of a UV-C pasteurization equipment and process for breast milk.