From Pathogens to Programs: A Case Study of Staphylococcus aureus within Bovine Milk at a Texas Panhandle Dairy Farm and the Genesis of a One Health Sciences Ph.D. Program

Staphylococcus aureus is an important mastitis causing pathogen in the dairy industry. Characterizing this pathogen is important for human and animal health due to its zoonotic potential. This dissertation investigated this pathogen within a Texas Panhandle dairy farm. The overall objective was to characterize S. aureus within quarter milk samples and to highlight the development of a Ph.D. program in One Health Sciences. The first study evaluated the prevalence, antimicrobial susceptibility, and genotypic characteristics of S. aureus from quarter milk samples in cows that had previously been diagnosed with S. aureus. A total of 314 quarter milk samples from 81 cows were taken and out of those, 150 were positive for S. aureus (47.8%) either as the singular causative agent or as a co-infection with another bacterial organism. Out of those 150 isolates, 136 (90.7%) were phenotypically resistant to penicillin and ampicillin. No other resistance was seen among the antimicrobials tested. Whole genome sequencing was conducted on a subset of 50 S. aureus isolates. There was a predominant sequence type (ST), as the majority (n=45, 90%) of isolates belonged to ST124. All these isolates also harbored the blaZ gene. We also identified 84 total virulence factors among the 50 isolates, and only 13 were not shared among all isolates. Virulence factors and antimicrobial resistance clustered based on identified ST. Additionally, one isolate belonging to ST1-t127 was identified, which also carried the seh gene. This gene encodes for an enterotoxin responsible for staphylococcal food poisoning. These results are important from a One Health perspective as they provide more information regarding the antimicrobial resistance and virulence potential of S. aureus for both human and animal populations. The second study conducted microbiome analysis via 16S rRNA gene sequencing on quarter milk samples. A total of 36 cows had 2 quarter milk samples analyzed each – one sample that was considered healthy and one that was considered mastitic due to a S. aureus infection. After conducting diversity analyses, we determined that the beta-diversity between the two groups (healthy vs. mastitic) were different. Samples from the healthy group had a higher abundance of the Achromobacter genus, while samples from the mastitic group had a higher abundance of Staphylococcus. These data may indicate an antagonistic relationship between Staphylococcus and Achromobacter; however, this data should be explored further. Both studies explored the pathogenic potential of S. aureus and share further insights of the pathogen in bovine milk. The last chapter explains the development of a Ph.D. program in One Health Sciences at Texas Tech University. We identified how the program was developed using published One Health core competencies. We also highlighted successes in the program and listed 7 areas that are opportunities for growth. One Health research is incredibly important as it hopes to integrate human, animal, and environmental health.

Embargo status: Restricted until 01/2027. To request the author grant access, click on the PDF link to the left.