Related Experiment Video

Updated: Jan 25, 2026

An Allelotyping PCR for Identifying Salmonella enterica serovars Enteritidis, Hadar, Heidelberg, and Typhimurium

An Allelotyping PCR for Identifying Salmonella enterica serovars Enteritidis, Hadar, Heidelberg, and Typhimurium

Published on: July 22, 2011

Molecular and Physiological Characterization of Fluoroquinolone-Highly Resistant Salmonella Enteritidis Strains

Sinisa Vidovic¹, Ran An¹, Aaron Rendahl¹

¹Department of Veterinary and Biomedical Sciences, University of Minnesota, Saint Paul, MN, United States.

Frontiers in Microbiology

|April 27, 2019

Abstract:

Four clinical isolates of Salmonella Enteritidis, susceptible to ciprofloxacin, and their spontaneous ciprofloxacin resistant (MICs from 8 to 16 μg/mL) and highly resistant (MIC 2048 μg/mL) mutants were used to gain an insight into the dynamics of development of fluoroquinolone (FQs) resistance in S. Enteritidis serovar. The first two high-frequency (i.e., mutations that occurred in each tested strain) mutations occurred in the gyrA, resulting in amino acid substitutions S83Y and S83F as well as D87G. Amino acid substitution D87G was significantly associated with the highly resistant mutants. Another high-frequency mutation, deletion in the ramRA intergenic region, was determined among the same group of highly resistant mutants. More importantly, each of these deletion mutations affected the RamR binding site. The effect of one 41 bp deletion mutation was empirically tested. The results showed that the deletion was responsible for resistance to ceftiofur and amoxicillin/clavulanic acid and decreased susceptibility to azithromycin and tetracycline. Performing gene expression assays across all ciprofloxacin susceptible groups, we found a consistent and significant upregulation of the ramA, acrB, and tolC (efflux pump associated genes) and downregulation of ompF (porin), clearly illustrating the importance of not only efflux but also porin-mediated permeability in the development of FQs resistance. Our data also showed that S. Enteritidis could acquire multiple mutations in QRDR region, further resulting in no up regulation of the ramA, acrB and tolC genes. These QRDR mutations and no activation of the AcrAB efflux pump seem to preserve the fitness of this organism compared to the S. Enteritidis strains that did not acquire multiple QRDR mutations. This report describes the dynamics of FQ-associated mutations in the highly resistant in FQ mutants in S. Enteritidis. In addition, we characterized a deletion in the ramRA integenic region, demonstrating that this frequent mutation in the highly resistant FQ mutants provide resistance or reduce susceptibility to multiple families of antibiotics.

Insights

Salmonella Enteritidis develops fluoroquinolone resistance through high-frequency gyrA mutations and ramRA deletions. These genetic changes impact multiple antibiotic classes, highlighting complex resistance dynamics.

Area of Science:

Microbiology
Molecular Biology
Antimicrobial Resistance

Background:

Fluoroquinolones (FQs) are critical antibiotics for treating Salmonella Enteritidis infections.
Understanding the genetic mechanisms of FQ resistance is crucial for effective treatment strategies.
Salmonella Enteritidis exhibits varying levels of resistance, necessitating detailed investigation into resistance development.

Purpose of the Study:

To investigate the dynamics of fluoroquinolone resistance development in Salmonella Enteritidis.
To identify key genetic mutations associated with high-level ciprofloxacin resistance.
To characterize the impact of specific mutations on the susceptibility to other antibiotic classes.

Main Methods:

Isolation and characterization of spontaneous ciprofloxacin-resistant and highly resistant mutants from clinical Salmonella Enteritidis isolates.
Sequencing of key genes (gyrA) and intergenic regions (ramRA) to identify mutations.
Gene expression analysis of efflux pump and porin-associated genes (ramA, acrB, tolC, ompF).
Phenotypic testing to determine antibiotic susceptibility profiles of resistant mutants.

Main Results:

High-frequency mutations in gyrA (S83Y, S83F, D87G) and deletions in the ramRA intergenic region were observed in resistant mutants.
The D87G substitution in gyrA was strongly associated with high-level resistance.
A specific 41 bp deletion in ramRA conferred resistance to ceftiofur and amoxicillin/clavulanic acid, and reduced susceptibility to azithromycin and tetracycline.
Upregulation of efflux pump genes (ramA, acrB, tolC) and downregulation of ompF were observed in susceptible strains, indicating the role of efflux and permeability.
Multiple QRDR mutations without efflux pump activation appeared to preserve bacterial fitness.

Conclusions:

Salmonella Enteritidis develops fluoroquinolone resistance through rapid acquisition of gyrA mutations and ramRA deletions.
The ramRA deletion is a significant contributor to multidrug resistance, affecting susceptibility to various antibiotic classes.
Understanding these resistance mechanisms is vital for monitoring and combating antimicrobial resistance in clinical settings.

Read full analysis

Keywords:

AcrAB efflux pump and small-colony variant phenotype OmpF porin Salmonella multidrug resistance quinolone resistance

More Related Videos

A Non-Coding Small RNA MicC Contributes to Virulence in Outer Membrane Proteins in Salmonella Enteritidis

A Non-Coding Small RNA MicC Contributes to Virulence in Outer Membrane Proteins in Salmonella Enteritidis

Published on: January 27, 2021

Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes

Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes

Published on: March 3, 2023

Related Concept Videos

Resistivity

Resistivity

When a voltage is applied to a conductor, an electrical field is generated, and charges in the conductor feel the force due to the electrical field. The current density that results depends on the electrical field and the properties of the material. In some materials, including metals at a given temperature, the current density is approximately proportional to the electrical field. In these cases, the current density can be modeled as:

Resistance

Resistance

When a current moves through any conductor, the conductor causes some level of difficulty for the current to flow. The measure of that difficulty is known as the resistance of the material and is represented by R. Every material has its own resistance. In the case of conductors, heat is emitted whenever a current passes through them. Resistance depends on the resistivity of the material. Resistivity is a characteristic of the material used to fabricate electrical components, whereas the...

Thermal Strain

Thermal Strain

Thermal strain is a concept that arises when we consider how temperature changes affect structures. Unlike the conventional assumption that structures remain constant under load, real-world scenarios often involve temperature fluctuations that can significantly impact these structures. Consider a homogeneous rod with a uniform cross-section resting freely on a flat horizontal surface. If the rod's temperature increases, the rod elongates. This elongation is proportional to the temperature...

Shearing Strain

Shearing Strain

The shearing strain represents a cubic element's angular change when subjected to shearing stress. This type of stress can transform a cube into an oblique parallelepiped without influencing normal strains. The cubic element experiences a significant transformation when exposed solely to shearing stress. Its shape alters from a perfect cube into a rhomboid, clearly demonstrating the effect of shearing strain. The degree of this strain is considered positive if it reduces the angle between the...

Measurements of Strain

Measurements of Strain

Strain quantifies the deformation of a material under force, typically measured as normal strain, which represents the change in length when compared with the original length. Electrical strain gauges are used for enhanced accuracy. These devices consist of a conductive wire mounted on a paper backing that adheres to the material's surface. These gauges operate on the piezoresistive effect, where the wire's electrical resistance changes in response to mechanical deformation. The strain...

Molecular Models

Molecular Models

Physical models representing molecular architectures of chemical compounds play essential roles in understanding chemistry. The use of molecular models makes it easier to visualize the structures and shapes of atoms and molecules.

Articles linked to this work by shared authors, journal, and citation graph.

Agreement between invasive and oscillometric blood pressure measurements during controlled haemorrhage in anaesthetised horses.

Equine veterinary journal·2026

Risk factors associated with introduction of wild-type porcine reproductive and respiratory syndrome (PRRS) virus into growing pigs in the Midwestern U.S.

Preventive veterinary medicine·2026

Retrospective Characterization of Clot Waveform Analysis in Canine Immune-Mediated Hemolytic Anemia Using the Turbidimetric ACL-TOP 300 Analyzer (2018-2022): 35 Cases.

Journal of veterinary emergency and critical care (San Antonio, Tex. : 2001)·2026

Investigating Multidrug-Resistant Bacteria in Canine Skin Infections at a Veterinary Teaching Hospital.

Journal of the American Animal Hospital Association·2026

Comparing Point-of-Care Ultrasound in Multiple Body Positions in Dogs to Key Cardiac Measurements by Echocardiography.

Veterinary sciences·2026

Utility of dynamic preload indices of hypovolemia in isoflurane-anesthetized horses.

Veterinary anaesthesia and analgesia·2026

See all related articles