Graduation Date

Fall 12-17-2021

Document Type


Degree Name

Doctor of Philosophy (PhD)


Medical Sciences Interdepartmental Area

First Advisor

W. Scott Campbell, Ph.D., MBA

Second Advisor

Trevor Van Schooneveld, MD, FACP

MeSH Headings

antibiogram, antibiotic, infection, antimicrobial stewardship, microbiology


Antibiograms are critical for choosing empiric antimicrobial therapy. Cumulative antibiograms, which aggregate susceptibility data, can mask differences within specific patient subsets or clinical syndromes. This dissertation was done to determine if antibiotic susceptibilities showed substantial differences when comparing stratified antibiograms to cumulative antibiograms.

Antibiotic susceptibility data was retrospectively obtained from Nebraska Medicine January 1, 2017 – December 31, 2019 for Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, and Enterococcus faecalis. The University of Nebraska Medical Center’s web antibiogram clinical decision support tool was used to export the data. Bacteria-antibiotic susceptibility rates of stratified antibiograms (patient location and specimen source) were compared using the chi-square test with a statistical significance at the

Some bacteria-antibiotic comparisons showed minimal differences (e.g., E. coli - gentamicin; K. pneumoniae - ampicillin-sulbactam; S. aureus - trimethoprim-sulfamethoxazole), while others showed a significant disagreement (e.g., E. coli – cefepime; P. aeruginosa – cefepime; K. pneumoniae - ceftriaxone; E. faecalis – levofloxacin; S. aureus – clindamycin). Combining specimen source and patient location resulted in the greatest number of significant changes. For example, the cumulative susceptibility of inpatient E. coli isolates to piperacillin-tazobactam was 87%, but when stratified by specimen source, susceptibility was only 74% in blood and 73% in respiratory specimens while it rose to 90% in urine (P < 0.001). Similarly, cumulative susceptibility of P. aeruginosa to cefepime among outpatients was 83%, while the blood and urine susceptibility were 93% and 91% respectively, but respiratory only reached 75% (P < 0.001). Significant differences among various bacterial species susceptibility demonstrated that stratified antibiograms are different from cumulative antibiograms, although there was no specific pattern of differences identified.

The results of this study showed that stratified antibiograms generate meaningful differences that may provide an opportunity for targeted empiric antibiotic prescribing depending on patient location and anticipated infection source. Future research is needed to determine what additional factors result in susceptibility differences for optimization of patient therapy.

Available for download on Tuesday, December 05, 2023