Defense Date


Document Type


Degree Type

Master of Science

Degree Name

Biological Sciences

First Advisor

Robert Smith, Ph. D.

Second Advisor

Katie Crump, Ph. D.

Third Advisor

Jose lopez, Ph. D.


Staphylococcus aureus, antibiotic resistance, inoculum effect, growth productivity, metabolism, growth rate


Antibiotic resistance is a major global public health concern, as bacteria have developed resistance to nearly every antibiotic currently on the market. The misuse of antibiotics, coupled with slow production and lack of new and effective drugs, leads to an increased risk of antibiotic-resistant bacterial infections and related fatalities. Therefore, it is crucial to understand the mechanism by which bacteria incur resistance to develop novel treatments, prevent further resistance, and extend the efficacy of our available antibiotics. One known mechanism bacteria use to incur resistance is the inoculum effect (IE), where higher initial density bacterial populations require greater drug concentrations to eliminate the population. Previous work established that growth productivity, the relationship between growth and metabolism, determines the strength of IE for multiple antibiotics in Escherichia coli. However, it remains unclear if the same metric could explain IE for Staphylococcus aureus. Accordingly, this research sought to investigate the effect of varying carbon sources and concentrations of casamino acids on the growth rate, metabolism, growth productivity, and IE of S. aureus. Our findings indicate that the carbon source in the growth medium determines growth rate, ATP concentration, and growth productivity. Cell density of high- and low-density S. aureus populations as a function of kanamycin concentration varies by metabolite and nitrogen source. From this, we found the minimum inhibitory concentration (MIC) and observed that ΔMIC varies for each carbon source depending on the casamino acid concentration used. Our results show that growth productivity predicts the strength of the inoculum effect in this pathogen. Notably, when S. aureus is grown with mannose, growth productivity is sufficiently high that the average ΔMIC decreases to a point where IE is essentially abolished. Overall, our work highlights the role of the growth environment in shaping growth productivity and, thus, the inoculum effect in S. aureus. Developments could contribute to novel approaches to combat high-density S. aureus infections while reducing IE in the clinic, in turn, increasing patient outcomes and preventing future resistance.


This work was supported by the National Institutes of Health award R15AI159902, President’s Faculty and Research Development Grant from Nova Southeastern University no. 334853, and by the Army Research Office under Grant Number W911NF-18-1-0443.



Available for download on Saturday, January 06, 2029