Related Experiment Video

Updated: Jun 24, 2026

Antimicrobial Synergy Testing by the Inkjet Printer-assisted Automated Checkerboard Array and the Manual Time-kill Method
12:03

Antimicrobial Synergy Testing by the Inkjet Printer-assisted Automated Checkerboard Array and the Manual Time-kill Method

Published on: April 18, 2019

Insights into the mechanisms underlying cell wall-active agents and gentamicin bactericidal synergism against

Paul Ugalde Silva1, Charlene Desbonnet1, Louis B Rice1

  • 1Department of Medicine, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, RI, USA.

The Journal of Antimicrobial Chemotherapy
|June 23, 2026
PubMed
Abstract

Insights

Cell wall inhibitors decrease intracellular pH in Enterococcus faecalis, enhancing aminoglycoside uptake. This finding explains the synergistic effect of combined therapies against these common healthcare-associated infections.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Pharmacology

Background:

  • Enterococcus faecalis causes healthcare-associated infections.
  • Reduced susceptibility to penicillins and high aminoglycoside MICs limit monotherapy.
  • Cell wall inhibitors and aminoglycosides show synergistic bactericidal activity, but the mechanism is unclear.

Purpose of the Study:

  • To investigate the link between synergistic activity of cell wall-active agents/aminoglycoside combinations and cell membrane energetics in E. faecalis.
  • To elucidate the mechanism of synergistic bactericidal activity.

Main Methods:

  • Broth microdilution MIC testing
  • Checkerboard assays
  • Time-kill assays
  • Fluorescent microscopy

Main Results:

  • Cell wall remodeling agents enhanced aminoglycoside uptake.
  • This uptake was facilitated by antibiotic-induced decreases in intracellular pH (pHi).

Conclusions:

  • Inhibiting cell wall synthesis decreases E. faecalis intracellular pH.
  • Cell wall remodeling is linked to ion transport and cytoplasmic acidification.
  • This acidification promotes aminoglycoside uptake, explaining synergistic effects.

Related Concept Videos

Inhibitors of Gram-positive Cell Wall Synthesis01:23

Inhibitors of Gram-positive Cell Wall Synthesis

Bacterial cell walls are typically rigid structures composed mainly of peptidoglycan, a mesh-like polymer that provides mechanical strength and maintains cell shape. The synthesis of peptidoglycan is a crucial process in bacterial growth and serves as a primary target for many antibiotics.Mechanism of Action of Beta-Lactam AntibioticsBeta-lactam antibiotics, such as penicillin, inhibit peptidoglycan synthesis in actively growing cells. These antibiotics share a characteristic four-membered...
Combined Effects of Drugs: Synergism01:27

Combined Effects of Drugs: Synergism

Synergism is a useful mechanism where combining two or more drugs is more effective than each constituent used alone. Such combinations are also called supra-additive interactions. The drugs collectively enhance the final therapeutic effect by acting on different targets. Another advantage is that the low dose of each constituent drug is sufficient to achieve the desired effect. This helps reduce the duration of therapy and lower the adverse effects of these drugs.
Such synergistic combinations...
Bacterial Cell Wall01:22

Bacterial Cell Wall

The bacterial cell wall is an essential structural component that encases the plasma membrane, preserving cellular integrity, determining shape, and protecting against osmotic stress. This rigid yet flexible structure primarily comprises peptidoglycan, a polymer that forms a mesh-like matrix conferring mechanical strength and flexibility.Peptidoglycan Composition and StructurePeptidoglycan, the core of the bacterial cell wall, comprises alternating units of N-acetylglucosamine (NAG) and...
Inhibitors of Bacterial Protein Synthesis01:25

Inhibitors of Bacterial Protein Synthesis

Aminoglycosides constitute a highly potent class of bactericidal antibiotics that exert their antimicrobial effects by targeting the bacterial ribosome, specifically disrupting protein synthesis. These polycationic molecules consist of amino-modified sugars linked via glycosidic bonds to an aminocyclitol core such as 2-deoxystreptamine or streptamine. Their strong positive charges facilitate tight binding to the negatively charged phosphate backbone of ribosomal RNA (rRNA), primarily at the 16S...
Clinical Significance of Antibiotic Resistance01:25

Clinical Significance of Antibiotic Resistance

Methicillin-resistant Staphylococcus aureus (MRSA) presents a critical public health threat, arising from its capacity to resist β-lactam antibiotics due to acquisition of the mecA gene within the staphylococcal cassette chromosome mec (SCCmec). This gene encodes penicillin-binding protein 2a (PBP2a), which impairs binding efficacy of methicillin and other β-lactams. MRSA has evolved into distinct clonal lineages impacting humans and animals alike, reinforcing its significance within the One...
Mechanism of Antibiotic Resistance in MRSA01:25

Mechanism of Antibiotic Resistance in MRSA

Antibiotic resistance in bacteria arises when microorganisms evolve the ability to withstand drugs designed to kill them or inhibit their growth, rendering once-effective treatments useless. This phenomenon, driven by genetic change and selection under antibiotic exposure, poses a profound threat to modern medicine. Mechanisms include drug-inactivating enzymes (e.g., β-lactamases), efflux pumps that eject antibiotics, mutations altering antibiotic targets, decreased drug uptake, and acquisition...