IDWeek 2026: Phage-Antibiotic Research and Nontoxigenic C diphtheriae in Albuquerque

Whole-genome sequencing can help researchers examine questions about potential treatment combinations and understand the strains circulating in a community. During an interview in the poster area at IDWeek 2026, held in Washington, DC, from October 21 to 24, Rachel Sidebottom, an MD-PhD student at the University of New Mexico School of Medicine, discussed her research, which explores both areas.

Sidebottom, whose PhD focuses on microbial genomics, described 3 conference presentations to Infection Control Today. Two of them are on her work on phage-antibiotic combinations, which incorporates whole-genome sequencing, time-kill analysis, and growth suppression assays to explore whether those features could inform a predictive model. She also discussed an investigation of nontoxigenic Corynebacterium diphtheriae that identified an ST5 strain circulating in Albuquerque, New Mexico.

Examining Why Some Isolates Respond

The phage-antibiotic study addressed the therapeutic challenge posed by MBL-PA. Researchers sought to characterize the activity of phage-antibiotic combinations and identify genomic features associated with susceptibility. Their broader goal is to establish a framework in which genomic characterization and phenotypic profiling of a clinical isolate could help guide treatment selection.

The team performed time-kill and growth suppression assays on 6 isolates from the CDC Antimicrobial Resistance Isolate Bank: AR243, AR245, AR248, AR242, AR231, and AR246. Testing assessed single phages, a phage cocktail, and combinations involving ciprofloxacin, cefepime, and meropenem. Whole-genome sequencing and comparative bioinformatic analyses examined phylogeny, phage-relevant virulence genes, and resistome profiles in relation to treatment response.

The results demonstrated substantial variation. AR243 and AR245 showed synergistic, bactericidal killing with the phage cocktail and cefepime, with reported Tukey-adjusted P values of less than .001 vs control. AR248 and AR242 responded to single-phage treatment, the cocktail, and ciprofloxacin-containing combinations, each with reported P values of less than .001. AR231 and AR246 showed no measurable response.

Responsive isolates shared broader repertoires of candidate phage-interaction genes, including loci associated with flagella, lipopolysaccharide, TonB-dependent receptors, pili, and pilus biogenesis. Closely related isolates also tended to share similar susceptibility patterns.

“These findings suggest that PAC efficacy is influenced by bacterial phylogeny and conserved surface features involved in phage attachment,” the study abstract states.

The findings support further exploration of genomic predictors of phage-antibiotic response. They describe laboratory activity across bacterial isolates, rather than demonstrated treatment outcomes in patients. Integrating these assays with whole-genome sequencing may help researchers develop more targeted approaches to selecting combinations for further evaluation.

Editor’s note: This interview was conducted in the poster area at IDWeek 2026. Questions have been added to organize the remarks.

ICT: Please introduce yourself and tell us about your research focus.

Rachel B. Sidebottom: Hi, my name is Rachel Sidebottom, and I’m an MD-PhD student at the University of New Mexico School of Medicine. My PhD is focusing on microbial genomics.

ICT: What are you presenting at IDWeek?

RS: Here at IDWeek, I have 3 presentations. The first presentation that I’m doing today is looking at using whole-genome sequencing, time-kill analysis, and growth suppression assays to learn more about phage-antibiotic combinations and whether or not we can use those features for a predictive model. I’m also presenting that as part of the rapid-fire poster presentations tomorrow.

ICT: What does your other presentation examine?

RS: Additionally, I have a third presentation where I’m looking at an outbreak of nontoxigenic Corynebacterium diphtheriae, where we found that there’s a specific strain circulating in Albuquerque, New Mexico, and it’s an ST5 strain.

ICT: What have you enjoyed most about attending IDWeek?

RS: The most important thing, or the most fun that I’m having here at IDWeek, is meeting all the amazing ID physicians, pharmacists, and partners. And I really liked the puppy playpen.

Sidebottom’s poster: “Predicting Phage-Antibiotic Combination Efficacy in Metallo-β-Lactamase-Producing Pseudomonas aeruginosa Using Whole Genome Sequencing, Growth Suppression, and Time-Kill Analysis,” was authored with Kasandra Velarde, MS, University of New Mexico College of Pharmacy in Albuquerque, New Mexico; Amer El Ghali, PharmD, University of New Mexico College of Pharmacy, Albuquerque, New Mexico; Daryl Domman, PhD, Los Alamos National Laboratory, in Los Alamos, New Mexico.

Another poster: William Johnson, MS, PhD, New Mexico Department of Health in Albuquerque, New Mexico; Anastacia Griego-Fisher, PhD, New Mexico Department of Health, Albuquerque, New Mexico; Amer El Ghali, PharmD, University of New Mexico College of Pharmacy, Albuquerque, New Mexico; Daryl Domman, PhD, Los Alamos National Laboratory in Los Alamos, New Mexico; Andrea Demeter, MD, Presbyterian Hospital, Albuquerque, New Mexico; John Fissel, PhD, D(ABMM), M(ASCP)CM, TriCore Reference Laboratories in Albuquerque, New Mexico; Meghan Brett, MD, Physician, University of New Mexico, in Albuquerque, New Mexico.