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Exploring the expanse and origin of antimicrobial resistance in infant formula milks Sian Cairns (24292325) PUREID: 663739372 Antimicrobial resistance microbiology infant formula milk powdered infant milk food microbiology food safety Powdered infant formula milk (PIF) is a popular early life feeding choice globally. However, infants fed PIF show an increased relative abundance of resistance genes in their gut. Antimicrobial resistant microbes have been recovered from PIF as it is not a sterile product. Similarly, antimicrobial resistant (AMR) bacteria and genes (ARGs) have been recovered from mother’s milk. ARGs from mother’s milk have been directly linked to those showing up in their infant’s gut resistome. However, research is lacking on the resistome of PIF and its link to infant gut development. The current research further addresses the extent of AMR in infant formula milk to understand its potential influence on infant gut resistome development.<br><br>The first two objectives of this study aimed to identify phenotypic and genotypic AMR in a range of PIF products available in the UK. This was achieved using aerobic culture, Matrix-Assisted Laser Desorption/Ionisation Time-ofFlight mass spectrometry (MALDI-ToF MS) identification and Kirby Bauer disk diffusion antimicrobial susceptibility tests. On comparison of different at home preparation methods for PIF (room temperature, 70°C or at home preparation machine (AHPM)), it was found that preparation method significantly impacted overall microbial recovery. <br><br>This was particularly relevant for the AHPM which recovered unique microbes indicating sterility issues with machine filters. This study also found opportunistic pathogens with resistance to carbapenems and thermotolerance above 70°C (NHS recommended preparation temperature) of common and concerning contaminants. This led into the second objective which looked to recover overall AMR microbes from PIF and analyse genotypic resistance. Five AMR genera were recovered including two demonstrating multidrug resistance. This study also found genotypic resistance in PIF DNA using a Polymerase Chain Reaction (PCR) approach and ARGs guided by bovine milk metagenome literature. <br><br>This included the recovery of a potentially mobilizable element. Therefore, these chapters show that PIF can be a source of AMR to infants. The next objective aimed to understand how infant formula milk (IFM) may impact the gut microbiome upon consumption. This was achieved by culturing susceptible Escherichia coli with ampicillin and IFM for six days. It was found that IFM supplementation appears to increase the rate of AMR to ampicillin in susceptible strains and that this effect is scalable with IFM concentration. <br><br>The final objective aimed to investigate the source of AMR in IFM by examining dairy farms. Unique silica nanoparticle encapsulated DNA (SPED) molecules were developed to provide safe synthetic tracers. These particles were tested in a care home environment and in a cattle crush. However, it was discovered that these particles are unsuitable for use in complex environments. AMR microbes in these environments were isolated using the same methods as in the first objectives. Additionally, microbes capable of surviving pasteurisation were found, including those present in bulk tank milk. There was species crossover with that recovered from PIF in earlier chapters.<br><br>This study has improved the overall understanding of IFM as a source of AMR in early life. Phenotypic and genotypic resistance was found in PIF with AMR linking back to the bovine milk metagenome and dairy farms. IFM also appears to directly impact AMR development in gut commensals. Therefore, this research indicates that IFM is a potential source of gut resistome development in infants from birth which may impact future health outcomes. 2026-10-01T16:18:00Z Text Thesis 10.17034/32805140.v1 https://figshare.com/articles/thesis/Exploring_the_expanse_and_origin_of_antimicrobial_resistance_in_infant_formula_milks/32805140 All Rights Reserved