Infant formula milk shows microbiological contaminants that are not removed using recommended preparation methods

Understanding the microbiota of powdered infant formula (PIF) products may provide important insights that are not seen with currently mandated microbiological testing. This work aimed to identify the load and taxonomy of microorganisms which persist through recommended preparation methods and increasingly popular at-home preparation machines (APHM).

PIFs were purchased from commercial suppliers to cover the majority of available brands and products in the UK. PIF was prepared using either advised sterile 70°C water, sterile room temperature water, or a popular AHPM. Preparations were plated onto Tryptic soy agar and Sabourhaud dextrose agar. Total aerobic counts were taken and isolates identified via MALDI-ToF mass spectrometry. Overall microbial populations were significantly different due to preparation method and bacterial populations were significantly different between PIFs (P < 0.05). Four PIFs showed within product significant differences caused by the preparation method. No significant difference occurred in microbe levels amongst brands and product types. AHPM prepared milks had unique microbial recoveries. Potential pathogens were isolated including Bacillus cereus resistant to imipenem and meropenem. B. cereus showed temperature resistance above the WHO recommended temperature of 70°C.

Current preparation guidance may not remove all microbial contaminants of PIFs, including the opportunistic pathogens identified in this work. These appear to be primarily environmental contaminants, and which may present a currently underappreciated concern with regards to infant microbiome development.