# Antibiotic resistance among hypermutator carbapenem resistant Klebsiella pneumoniae

> **NIH NIH R21** · UNIVERSITY OF PITTSBURGH AT PITTSBURGH · 2022 · $260,209

## Abstract

Project Summary
Carbapenem resistant Enterobacteriaceae (CRE) are major public health threats. CR-Klebsiella pneumoniae
(CRKP) are the most common CRE globally. Treatment of CRKP and other CRE infections with new antibiotics
like ceftazidime-avibactam (CZA) and meropenem-vaborbactam (MVB) has improved survival, but recurrent
infections are common and emergent resistance is problematic. CRE infections are usually due to strains that
colonize the GI tract. Among other bacteria, it is now apparent that GI colonization is caused by a population of
closely related, but genetically distinct strains. These strains can exhibit a range of antibiotic resistance and
biologic attributes, which are often not appreciated by studying single colonies from microbiologic cultures. In
studies of natural bacterial populations, ~1 to 5% of isolates exhibit high spontaneous mutation rates, which may
confer selective advantages under environmental stress and increase diversity within the population. Such
hypermutation (HM) strains are most prevalent in humans during chronic colonization and recurrent infections,
and they most often stem from mutations to DNA mismatch repair (MMR) genes like mutS, mutL or mutH. There
are few studies of HM among CRKP or CRE. We believe that HM is under-recognized in these bacteria because
studies have not assessed long-term GI colonization, recurrent infections, or populations of strains from clinical
samples. In this project, we hypothesize that 1) HM CRKP can be recovered from patients with chronic GI
colonization and persistent/recurrent infections; 2) MMR and other gene mutations promote HM in vitro, and CZA
and MVB resistance in vitro and within infected organs; and 3) these mutations promote transmission and receipt
of antibiotic resistance gene (ARG)-bearing plasmids by CRKP in vitro and during GI colonization. In pilot
screening studies, we recovered HM CRKP from ~30% of patients with chronic GI colonization, or persistent or
recurrent infections. MMR gene mutations were identified in most HM CRKP strains. One of these mutations
(MutH V76G) was proven to contribute to HM, MVB and CZA resistance, and enhanced transfer and acceptance
of plasmids containing ARGs in vitro, and to CRKP tissue burdens and emergence of MVB resistance within
infected organs of intravenously (IV)-infected mice. In aim 1 of this proposal, we will continue to screen clinical
CRKP isolates for HM phenotype. We will perform whole genome sequencing on HM isolates, and create
isogenic mutant strains to determine if certain mutations contribute to HM. In aim 2, we will evaluate the role of
HM mutations in emergence of CZA, MVB and colistin resistance in vitro and within mouse organs following IV
infection. Then, we will determine impact of HM mutations on transfer of ARG-bearing plasmids in vitro and
during mouse GI colonization. This project will mark the first systematic investigations of CRE clinical isolates
for HM phenotypes. If successful, experiments will...

## Key facts

- **NIH application ID:** 10532461
- **Project number:** 1R21AI166847-01A1
- **Recipient organization:** UNIVERSITY OF PITTSBURGH AT PITTSBURGH
- **Principal Investigator:** M. Hong Thi NGUYEN
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $260,209
- **Award type:** 1
- **Project period:** 2022-06-21 → 2024-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10532461

## Citation

> US National Institutes of Health, RePORTER application 10532461, Antibiotic resistance among hypermutator carbapenem resistant Klebsiella pneumoniae (1R21AI166847-01A1). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/10532461. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*