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Antibiotics
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Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology
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Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology

A special issue of Antibiotics (ISSN 2079-6382). This special issue belongs to the section "Mechanism and Evolution of Antibiotic Resistance".

Deadline for manuscript submissions: 31 July 2026 | Viewed by 17452

Special Issue Editor

Prof. Dr. Owen B. Spiller

E-Mail Website
Guest Editor
1. Medical Microbiology, Division of Infection and Immunity, Cardiff University, Cardiff, UK
2. Bacteriology Reference Department, UK Health Security Agency, London, UK
Interests: antimicrobial resistance; neonatal sepsis; Ureaplasma; Mycoplasma; coagulase-negative staphylococci; legionella; group b streptococcus; Enterococcus spp.; Staphylococcus haemolyticus
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues, 

The rise of antimicrobial resistance (AMR) is one of the most pressing global health challenges of our time. The accurate and reliable detection of antimicrobial susceptibility and resistance is critical for guiding effective treatment strategies and curbing the spread of resistant pathogens. However, discrepancies in diagnostic methods, lack of standardisation, and limited access to advanced technologies in resource-limited settings hinder our ability to monitor and respond to AMR effectively.

This Special Issue aims to explore the latest advancements in antimicrobial susceptibility and resistance detection methodologies, focusing on the need for improved standardisation and consistency across clinical, environmental, and veterinary settings. Contributions are welcome to highlight innovative technologies, diagnostic platforms, and laboratory techniques that can enhance the accuracy, speed, and accessibility of AMR detection. Additionally, this Special Issue aims to address the challenges of validating these methodologies across diverse pathogen species, resistance mechanisms, and geographical regions.

We invite contributions that address, but are not limited to, the following topics:

  • Novel technologies for antimicrobial susceptibility testing (AST), such as next-generation sequencing, microfluidics, and biosensors.
  • Standardisation of AST protocols across clinical, veterinary, and environmental microbiology laboratories.
  • Comparative studies of traditional and emerging methods for AMR detection.
  • Point-of-care diagnostic tools for rapid and accurate AMR detection.
  • Quality assurance and control in AMR diagnostics.
  • The role of big data, machine learning, and artificial intelligence in improving resistance surveillance and prediction.
  • Global challenges in implementing standardised AMR detection in low-resource settings.

Through this Special Issue, we hope to promote the development of more robust and widely accessible detection methods, facilitating global efforts to fight AMR and improve patient outcomes. By standardising diagnostic approaches and embracing technological innovation, we can move closer to providing an effective response to one of the most urgent health threats of the 21st century.

Prof. Dr. Owen B. Spiller
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Antibiotics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2900 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • antimicrobial susceptibility testing
  • resistance screening
  • rapid diagnostics
  • clinical
  • veterinary
  • environmental
  • validation

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Published Papers (11 papers)

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Research

15 pages, 1136 KB  
Article
MYCOPLASMA IST3 Results and Antimicrobial Susceptibility in PCR-Positive Urine Samples for Ureaplasma spp.
by Rukiye Berkem and Tuğçe Özyol Atkaya
Antibiotics 2026, 15(3), 285; https://doi.org/10.3390/antibiotics15030285 - 11 Mar 2026
Viewed by 812
Abstract
Background: Ureaplasma spp. and Mycoplasma hominis are urogenital pathogens that may be missed by routine culture, particularly in patients with genitourinary symptoms in whom conventional methods fail to identify an etiologic agent. Limited routine implementation of targeted diagnostics and antimicrobial susceptibility testing (AST) [...] Read more.
Background: Ureaplasma spp. and Mycoplasma hominis are urogenital pathogens that may be missed by routine culture, particularly in patients with genitourinary symptoms in whom conventional methods fail to identify an etiologic agent. Limited routine implementation of targeted diagnostics and antimicrobial susceptibility testing (AST) for these organisms may contribute to diagnostic uncertainty and treatment failure. Methods: Seventy-five midstream urine samples submitted for suspected urinary tract infection and positive for Ureaplasma spp. according to a q-PCR urinary panel (Bioeksen, İstanbul, Türkiye) were tested the same day with MYCOPLASMA IST3 (bioMérieux, Marcy-l’Étoile, France) to assess growth and antimicrobial susceptibility. Results: q-PCR detected U. parvum in 54/75 (72%), U. urealyticum in 15/75 (20%), and both species in 6/75 (8%); M. hominis was not included in the PCR panel. MYCOPLASMA IST3 showed growth in 70/75 samples (positive percent agreement, 93.33%), while 5/75 (discordance, 6.66%) showed no growth. Among culture-positive samples, 57/70 (81.42%) yielded Ureaplasma spp. alone, and 13/70 (18.58%) yielded Ureaplasma spp. together with M. hominis. Resistance to levofloxacin and tetracycline was observed in 15.7% and 12.9% of Ureaplasma spp. isolates, respectively; resistance to moxifloxacin, erythromycin, and telithromycin was observed in 2.9% of isolates for each agent. In M. hominis isolates, no resistance to levofloxacin, moxifloxacin, or tetracycline was observed, whereas clindamycin resistance was observed in 7.7% of isolates. Conclusions: In addition to intrinsic resistance, acquired antimicrobial resistance in Ureaplasma and Mycoplasma species appears to be increasing; therefore, treatment decisions should be guided by AST whenever feasible. Clinical laboratories should implement appropriate diagnostic methods for these organisms and perform susceptibility testing when indicated to support clinical decision making and optimize antimicrobial selection. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
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12 pages, 485 KB  
Article
In Vitro Activity of Cefiderocol, Eravacycline, and Imipenem–Relebactam Against Multidrug-Resistant Acinetobacter baumannii Clinical Isolates
by Yasemin Bölükbaşı and Betigül Öngen
Antibiotics 2026, 15(3), 246; https://doi.org/10.3390/antibiotics15030246 - 27 Feb 2026
Viewed by 682
Abstract
Background/Objectives: Acinetobacter baumannii is a leading cause of healthcare-associated infections and is frequently associated with multidrug resistance, severely limiting therapeutic options. The increasing prevalence of carbapenem-resistant A. baumannii (CRAB) has intensified interest in novel antimicrobial agents such as cefiderocol, eravacycline, and imipenem–relebactam. [...] Read more.
Background/Objectives: Acinetobacter baumannii is a leading cause of healthcare-associated infections and is frequently associated with multidrug resistance, severely limiting therapeutic options. The increasing prevalence of carbapenem-resistant A. baumannii (CRAB) has intensified interest in novel antimicrobial agents such as cefiderocol, eravacycline, and imipenem–relebactam. Methods: A total of 80 multidrug-resistant (MDR) A. baumannii isolates recovered from various clinical specimens between April 2019 and October 2023 were included. Antimicrobial susceptibility testing was performed using disk diffusion, gradient test, and broth microdilution methods in accordance with EUCAST and CLSI recommendations. The minimum inhibitory concentrations (MIC’s) for cefiderocol were evaluated with broth microdilution using iron-depleted cation-adjusted Mueller–Hinton broth as the reference method. The presence of carbapenem resistance–associated genes (blaOXA-23, blaOXA-24, blaOXA-51, blaOXA-58, blaIMP, and tetA) was investigated by polymerase chain reaction. Results: All isolates were resistant to imipenem and meropenem. Colistin resistance was detected in 7.5% of isolates. According to EUCAST criteria, cefiderocol susceptibility was observed in 77.5% of isolates by microdilution and in 81.25% by disk diffusion. Eravacycline demonstrated low MIC values, with MIC50 and MIC90 of 0.25 mg/L and 0.75 mg/L, respectively. In contrast, all isolates were resistant to imipenem–relebactam. The blaOXA-23 gene was detected in 82.5% and blaOXA-24 in 17.5% of isolates, while no blaOXA-58, blaIMP, or tetA genes were identified. No statistically significant association was found between cefiderocol resistance and OXA-type carbapenemase genes. Conclusions: Cefiderocol and eravacycline demonstrated promising in vitro activity against MDR A. baumannii, including colistin-resistant isolates, whereas imipenem–relebactam showed no activity. These findings support the potential role of cefiderocol and eravacycline as alternative treatment options for CRAB infections and highlight the multifactorial nature of cefiderocol resistance beyond OXA-type carbapenemase production. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
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15 pages, 1954 KB  
Article
Molecular Identification, Virulence Factors, and Antifungal Susceptibility Profiles of Candida Isolates from Clinical Samples of Intensive Care Patients
by Zeynep Çelik, İbrahim Halil Kılıç, Semih Tokak and Fatma Esenkaya Taşbent
Antibiotics 2026, 15(2), 197; https://doi.org/10.3390/antibiotics15020197 - 10 Feb 2026
Cited by 1 | Viewed by 912
Abstract
Background/Objectives:  Candida infections constitute a significant category of healthcare-associated infections. In studies aiming to develop new antifungal agents against Candida species, the importance of their virulence factors has been emphasized. Methods: This study included 100 Candida isolates obtained from patients hospitalized in [...] Read more.
Background/Objectives:  Candida infections constitute a significant category of healthcare-associated infections. In studies aiming to develop new antifungal agents against Candida species, the importance of their virulence factors has been emphasized. Methods: This study included 100 Candida isolates obtained from patients hospitalized in intensive care units. Standard microbiological and molecular methods were employed for species identification. Virulence factors were determined through protease, phospholipase, hemolysis, and biofilm activity assays per-formed on the Candida strains. The EUCAST liquid microdilution method was used to assess antifungal susceptibility. Results: Based on sequencing results, 39 isolates were identified as Candida albicans and 61 as non-albicans Candida species. The accuracy of species identification was found to be 71% for Chromagar Candida and 87% for the MALDI-TOF MS system, compared to sequencing. Protease activity was positive in 52% of the isolates, phospholipase in 42%, hemolytic activity in 77%, and biofilm formation in 48%. Kruskal–Wallis analysis revealed no statistically significant interspecies differences in MIC distributions for amphotericin B, fluconazole, itraconazole, or nystatin (p > 0.05), although species-specific trends were observed, with higher fluconazole MICs in C. albicans and lower MIC values in C. tropicalis.  Conclusions: Determining the distribution of Candida species, as well as their virulence factors and antifungal MIC profiles, is of great importance for developing appropriate treatment strategies and reducing related morbidity and mortality. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
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9 pages, 524 KB  
Article
Loss-of-Function Mutations in the Penicillin-Binding Protein PonA1 Confer Agar-Dependent Resistance to Durlobactam in Mycobacterium abscessus
by Dereje Abate Negatu, Wassihun Wedajo Aragaw, Min Xie, Véronique Dartois and Thomas Dick
Antibiotics 2026, 15(1), 7; https://doi.org/10.3390/antibiotics15010007 - 20 Dec 2025
Viewed by 1338
Abstract
Background: Infections caused by the multidrug-resistant pathogen Mycobacterium abscessus (Mab) are notoriously difficult to treat. The novel β-lactamase inhibitor durlobactam, in combination with β-lactams, shows potent bactericidal activity against Mab, but the potential for acquired resistance remains a clinical [...] Read more.
Background: Infections caused by the multidrug-resistant pathogen Mycobacterium abscessus (Mab) are notoriously difficult to treat. The novel β-lactamase inhibitor durlobactam, in combination with β-lactams, shows potent bactericidal activity against Mab, but the potential for acquired resistance remains a clinical concern. Objectives: To identify and characterize mechanisms of acquired resistance to durlobactam in Mab. Methods: In vitro single-step resistance selection was performed by plating wild-type Mab ATCC 19977 and by transcriptional silencing using a CRISPR interference (CRISPRi) system. Minimum inhibitory concentrations (MICs) were determined by both an agar-based method and broth microdilution. Results: Whole-genome sequencing of durlobactam-resistant mutants identified loss-of-function mutations in ponA1, a gene encoding a class A penicillin-binding protein involved in cell wall synthesis. Targeted deletion of ponA1 (ΔponA1) and CRISPRi-mediated knockdown of ponA1 expression both recapitulated the resistance phenotype, resulting in a significant increase in the durlobactam MIC on solid agar media. Strikingly, broth microdilution MICs remained largely unaffected. Conclusions: Inactivation of the peptidoglycan synthase PonA1 is a novel mechanism of resistance to durlobactam in Mab that is phenotypically expressed only during growth on solid surfaces. This finding identifies a specific genetic pathway for resistance and highlights that standard broth-based susceptibility testing could miss clinically relevant resistance mechanisms. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
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11 pages, 1086 KB  
Article
An Algorithm for Rapid and Low-Cost Detection of Carbapenemases Directly from Positive Blood Cultures Using an Immunochromatographic Test
by Patricia del Carmen García, Pamela Rojas, Ana María Guzmán, Sofía Paz Torres and Aniela Wozniak
Antibiotics 2026, 15(1), 1; https://doi.org/10.3390/antibiotics15010001 - 19 Dec 2025
Viewed by 752
Abstract
Background/Objectives: Detection of carbapenemases (KPC, OXA-48, VIM, IMP, NDM) from blood cultures (BCs) by standard methods takes 48–72 h and includes BC seeding, susceptibility testing and carbapenemase detection. Automated qPCR panels provide results in 1 h but are very costly. We aim [...] Read more.
Background/Objectives: Detection of carbapenemases (KPC, OXA-48, VIM, IMP, NDM) from blood cultures (BCs) by standard methods takes 48–72 h and includes BC seeding, susceptibility testing and carbapenemase detection. Automated qPCR panels provide results in 1 h but are very costly. We aim to evaluate a low-cost and rapid immunochromatographic (IC) test directly from positive BCs using the reference method as a comparator. Methods: Ninety-one positive BCs from real-world patients and sixty-four simulated BCs were included. BC broth was treated with SDS and washed before analysis with the K.N.I.V.O. carbapenemase detection IC test. Discordant results were confirmed through the NG Carba-5 IC test and GeneXpert Carba-R qPCR test. Results: The test detected 100% of the 87 carbapenemase-producing BCs tested (sensitivity: 100% [CI95%: 95.8–100%]). However, 13 BCs generated false positive bands for NDM and/or OXA-48 (specificity: 80.8% [CI95%: 69.5–89.4%). The positive and negative predictive values were 87.0% (CI95%: 80.4–91.6%) and 100% (CI95%: 93.5–100%). Analysis of BCs providing false positive results through both confirmatory tests showed that BCs were negative for these carbapenemases. Conclusions: This is the first evaluation of the K.N.I.V.O. IC test directly from positive BCs, with a pragmatic confirmation algorithm using a second IC test or qPCR in case of NDM or OXA-48, that addresses K.N.I.V.O.’s specificity gap. The main limitation of this work is that confirmatory testing was performed only in false positives. The implementation of the K.N.I.V.O. IC test would contribute to early carbapenemase detection in BCs and is an alternative for low-resource hospitals where qPCR panels are not available. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
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20 pages, 5934 KB  
Article
Antimicrobial Susceptibility Determination of Less Frequently Isolated Legionella Species by Broth and Agar Dilution
by Caitlin Farley, Amy Price, Max Sewell, Rachael Barton, Edward A. R. Portal, Ian Boostrom, Jessica Day, Baharak Afshar, Victoria J. Chalker and Owen B. Spiller
Antibiotics 2025, 14(11), 1165; https://doi.org/10.3390/antibiotics14111165 - 17 Nov 2025
Viewed by 1287
Abstract
Background/Objectives: Infections caused by Legionella species are primarily associated with Legionella pneumophila, but non-pneumophila species are increasingly implicated in human disease. Despite this, antimicrobial susceptibility testing (AST) data for non-pneumophila species remain scarce, and standardised testing protocols or resistance [...] Read more.
Background/Objectives: Infections caused by Legionella species are primarily associated with Legionella pneumophila, but non-pneumophila species are increasingly implicated in human disease. Despite this, antimicrobial susceptibility testing (AST) data for non-pneumophila species remain scarce, and standardised testing protocols or resistance thresholds have not been established. This study aimed to address this gap by evaluating and comparing AST performance for non-pneumophila Legionella species relative to L. pneumophila using three methodologies. Methods: AST was conducted on 89 Legionella isolates using LASARUS agar dilution, buffered yeast extract broth microdilution (BYE-BMD), and BCYE-α agar dilution, against ampicillin, azithromycin, chloramphenicol, doxycycline, levofloxacin, and rifampicin. Growth performance and minimum inhibitory concentrations (MICs) were assessed after a 96 h incubation. Results: MIC profiles were obtained using LASARUS and BYE-BMD for 53.9% and 93.3% of isolates, respectively. While L. pneumophila reached sufficient turbidity in BYE-BMD after a 48 h incubation, non-pneumophila species required an extended incubation (72–96 h). Non-pneumophila species displayed broader MIC ranges against azithromycin (0.016–1 mg/L) and levofloxacin (0.016–0.25 mg/L), but a narrower rifampicin range (≤0.0005–0.032 mg/L) relative to L. pneumophila. L. longbeachae exhibited a higher MIC50 for rifampicin despite overlapping susceptibility ranges across all species (0.001–0.016 mg/L). Conclusions: This study demonstrates species-specific differences in Legionella susceptibility and highlights the limitations in extrapolating L. pneumophila-based AST data. Azithromycin MICs in non-pneumophila species exceeded those of L. pneumophila, raising clinical concern. While BYE-BMD was the most effective method for MIC determination, three species required BCYE-α due to poor growth. These findings support developing standardised, species-specific AST protocols and thresholds amid rising macrolide resistance and the increasing detection of non-pneumophila infections. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
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16 pages, 3329 KB  
Article
Comparison of Phenotypic and Whole-Genome Sequencing-Derived Antimicrobial Resistance Profiles of Legionella pneumophila Isolated in England and Wales from 2020 to 2023
by Rediat Tewolde, Rebecca Thombre, Caitlin Farley, Sendurann Nadarajah, Ishrath Khan, Max Sewell, Owen B. Spiller and Baharak Afshar
Antibiotics 2025, 14(10), 1053; https://doi.org/10.3390/antibiotics14101053 - 21 Oct 2025
Cited by 2 | Viewed by 1470
Abstract
Background: Antimicrobial resistance (AMR) in Legionella pneumophila is emerging as a concern, particularly with resistance to macrolides and fluoroquinolones. Although clinically significant resistance in Legionella pneumophila remains uncommon, systematic genomic surveillance using whole-genome sequencing (WGS) is needed to anticipate treatment failure as metagenomic [...] Read more.
Background: Antimicrobial resistance (AMR) in Legionella pneumophila is emerging as a concern, particularly with resistance to macrolides and fluoroquinolones. Although clinically significant resistance in Legionella pneumophila remains uncommon, systematic genomic surveillance using whole-genome sequencing (WGS) is needed to anticipate treatment failure as metagenomic diagnostics move toward routine use. Objectives: We assessed the UK Health Security Agency AMR pipeline for predicting resistance in L. pneumophila by analysing 522 L. pneumophila isolates from England and Wales (2020–2023) together with nine database sequences that carry confirmed 23S rRNA mutations conferring high-level azithromycin resistance. The objective of the present study was to examine the presence of antimicrobial resistance genes (ARGs) in L. pneumophila isolates and to determine whether they exhibited phenotypic resistance through minimum inhibitory concentration (MIC) testing. Methods: Serogroups (sgs) were determined using an in-house qPCR assay, and L. pneumophila non-sg1 isolates were serogrouped using the Dresden monoclonal antibody (mAb) typing method. Sequence types were determined using the standard sequence-based typing method by Sanger sequencing. WGS reads were screened against standard AMR databases to identify resistance genes and resistance-mediating mutations. Agar dilution measured MICs for azithromycin, erythromycin, ampicillin, levofloxacin, tetracycline and spectinomycin in isolates possessing the blaOXA-29, lpeAB or aph(9)-Ia gene. Results: AMR screening detected lpeAB, two allelic β-lactamase variants (blaOXA-29 and blaLoxA) and aph(9)-Ia in 165 of the 522 L. pneumophila isolates, while all high-azithromycin MIC reference sequences contained the expected 23S mutation. Only lpeAB was associated with a significant twofold elevation in macrolide MICs. Neither β-lactamase variant increased ampicillin MICs, and aph(9)-Ia carriage did not correlate with higher spectinomycin MICs. Conclusions: Advanced genomic analytics can now deliver timely therapeutic guidance, yet database-flagged genes may not translate into phenotypic resistance. Continuous pairing of curated mutation catalogues with confirmatory testing remains essential for distinguishing clinically actionable determinants such as 23S mutations and lpeAB from silent markers like blaOXA-29 and aph (9)-Ia. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
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11 pages, 260 KB  
Article
Evaluation of the NG-Test CARBA 5 for Rapid Detection of Carbapenemases in Clinical Isolates of Klebsiella pneumoniae
by Bojan Rakonjac, Momčilo Djurić, Danijela Djurić-Petković, Jelena Dabić, Marko Simonović, Marija Milić and Aleksandra Arsović
Antibiotics 2025, 14(10), 989; https://doi.org/10.3390/antibiotics14100989 - 2 Oct 2025
Cited by 2 | Viewed by 2241
Abstract
Background: Carbapenem-resistant Klebsiella pneumoniae (CRKp) is a critical global health threat due to its multidrug resistance, primarily driven by carbapenemase production. Rapid and accurate detection of carbapenemases is essential for effective treatment and infection control. This study evaluates the validity of the NG-Test [...] Read more.
Background: Carbapenem-resistant Klebsiella pneumoniae (CRKp) is a critical global health threat due to its multidrug resistance, primarily driven by carbapenemase production. Rapid and accurate detection of carbapenemases is essential for effective treatment and infection control. This study evaluates the validity of the NG-Test CARBA 5, a rapid immunochromatographic assay, for detecting five major carbapenemases (KPC, NDM, VIM, IMP, OXA-48-like) in clinical CRKp isolates. Methods: Clinical isolates of CRKp were collected from various clinical specimens at the Military Medical Academy in Belgrade, Serbia, between January 2023 and October 2024. Detection of carbapenemases was performed using NG-Test CARBA 5, while PCR served as the reference method. Diagnostic performance was assessed by calculating sensitivity, specificity, and Cohen’s kappa coefficient. Results: Among 312 isolates, OXA-48-like was the most prevalent carbapenemase. NG-Test CARBA 5 showed high sensitivity (98.7%) and specificity (100%) overall, with excellent agreement for NDM (κ = 0.947), OXA-48-like (κ = 0.957), and KPC (κ = 0.978). However, it failed to detect VIM in five PCR-positive isolates, suggesting potential limitations. Conclusions: NG-Test CARBA 5 is a rapid and reliable tool for detecting major carbapenemases in CRKp, though its performance for VIM detection requires further investigation. This assay has the potential to improve clinical diagnostics and strengthen infection control in settings with high antimicrobial resistance. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
11 pages, 1198 KB  
Article
Evaluation of a Novel Rapid Phenotypic Antimicrobial Susceptibility Testing System
by Yuan-Chao Xue, Filipe Cerqueira, Natalie Williams-Bouyer and Ping Ren
Antibiotics 2025, 14(10), 962; https://doi.org/10.3390/antibiotics14100962 - 25 Sep 2025
Cited by 1 | Viewed by 2654
Abstract
Background/Objectives: Phenotypic antimicrobial susceptibility testing (AST) is essential for guiding timely and effective antibiotic therapy. Rapid and accurate reporting of AST results enables earlier optimization of treatment and supports antimicrobial stewardship by minimizing unnecessary use of broad-spectrum antibiotics. This study aimed to evaluate [...] Read more.
Background/Objectives: Phenotypic antimicrobial susceptibility testing (AST) is essential for guiding timely and effective antibiotic therapy. Rapid and accurate reporting of AST results enables earlier optimization of treatment and supports antimicrobial stewardship by minimizing unnecessary use of broad-spectrum antibiotics. This study aimed to evaluate the performance of the Selux DX Next-Generation Phenotyping AST system in comparison with the standard-of-care MicroScan WalkAway Plus system and broth microdilution reference results. Methods: A total of 332 clinical isolates and 97 Antimicrobial Resistance (AR) Bank reference isolates were tested using the Selux DX and MicroScan systems. Performance was assessed by categorical agreement (CA), error rates [very major errors (VMEs), major errors (MEs), minor errors (mEs)], and turnaround time. Results: The Selux DX system demonstrated ≥90% CA for most drug–organism combinations, consistent with Clinical and Laboratory Standards Institute (CLSI) acceptance thresholds, although elevated error rates were noted for erythromycin, aztreonam, cefazolin, minocycline, and ampicillin/sulbactam. Across 5124 drug–bug combinations, 55 VMEs (1.1%), 42 MEs (0.8%), and 203 mEs (4.0%) were identified. The Selux DX system achieved a markedly shorter average turnaround time of 5.5 h compared with 16 h for the MicroScan system, though at the cost of a longer setup time. Conclusions: The Selux DX system provides rapid and reliable phenotypic AST results, supporting earlier clinical decision-making and antimicrobial stewardship. However, discrepancies with certain antimicrobial agents, particularly among highly resistant reference isolates, highlight the need for further validation in larger, multicenter studies. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
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9 pages, 421 KB  
Article
Increase in Penicillin Non-Susceptibility in Group B Streptococci Alongside Rising Isolation Rates—Based on 24 Years of Clinical Data from a Single University Hospital
by Sunghwan Shin, Dong Hee Whang, Tae-Hyun Um, Chong Rae Cho and Jeonghyun Chang
Antibiotics 2025, 14(9), 928; https://doi.org/10.3390/antibiotics14090928 - 13 Sep 2025
Cited by 1 | Viewed by 1574
Abstract
Background/Objectives: Streptococcus agalactiae (Group B Streptococci, GBS) is Gram-positive, beta-hemolytic coccus known to be transmitted by vertical transmission in neonates during birth with neonatal sepsis, pneumonia, and meningitis. In adults, particularly the elderly and those with diabetes mellitus, GBS can also cause [...] Read more.
Background/Objectives: Streptococcus agalactiae (Group B Streptococci, GBS) is Gram-positive, beta-hemolytic coccus known to be transmitted by vertical transmission in neonates during birth with neonatal sepsis, pneumonia, and meningitis. In adults, particularly the elderly and those with diabetes mellitus, GBS can also cause pneumonia and sepsis. Penicillin is the drug of choice, and GBS is generally susceptible to this antibiotic. This study investigates trends in GBS isolation rates and penicillin non-susceptibility over time at a university hospital. Methods: We retrospectively analyzed 24 years (2000–2023) of microbiological data from Ilsan Paik Hospital to investigate trends in GBS isolation and penicillin susceptibility. Isolates were identified and tested using the Vitek 2 system, following CLSI guidelines. WHONET 2023 was used for data aggregation and analysis. Trends were analyzed by dividing the study period into three intervals: Period 1 (2000–2009), Period 2 (2010–2019), and Period 3 (2020–2023). Antimicrobial susceptibility rates for total GBS and PCN-NS GBS (penicillin non-susceptible group B Streptococcus) were compared using chi-square tests. Results: Among 257,884 total isolates, 3003 (1.16%) were GBS, and 29 (0.97%) were PCN-NS. GBS and PCN-NS isolation rates increased significantly across the three periods (p = 0.0001 and p = 0.009, respectively). PCN-NS GBS showed reduced susceptibility to all tested antimicrobials, with no drug showing higher susceptibility compared to total GBS. Conclusions: This study demonstrates a statistically significant rise in both GBS isolation rate and penicillin non-susceptibility over time. Given the emergence of multidrug-resistant GBS strains, susceptibility testing and interdisciplinary collaboration between microbiologists and clinicians are critical to guiding effective antimicrobial therapy and preventing neonatal and adult GBS infections. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
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17 pages, 2176 KB  
Article
Growth-Phase-Dependent Modulation of Quorum Sensing and Virulence Factors in Pseudomonas aeruginosa ATCC 27853 by Sub-MICs of Antibiotics
by Ahmed Noby Amer, Nancy Attia, Daniel Baecker, Rasha Emad Mansour and Ingy El-Soudany
Antibiotics 2025, 14(7), 731; https://doi.org/10.3390/antibiotics14070731 - 21 Jul 2025
Cited by 7 | Viewed by 2695
Abstract
Background: Antibiotics at sub-inhibitory concentrations can rewire bacterial regulatory networks, impacting virulence. Objective: The way that exposure to selected antibiotics (ciprofloxacin, amikacin, azithromycin, ceftazidime, and meropenem) below their minimum inhibitory concentration (sub-MIC) modulates the physiology of Pseudomonas aeruginosa is examined in [...] Read more.
Background: Antibiotics at sub-inhibitory concentrations can rewire bacterial regulatory networks, impacting virulence. Objective: The way that exposure to selected antibiotics (ciprofloxacin, amikacin, azithromycin, ceftazidime, and meropenem) below their minimum inhibitory concentration (sub-MIC) modulates the physiology of Pseudomonas aeruginosa is examined in this study using growth-phase-resolved analysis. Methods: Standard P. aeruginosa strain cultures were exposed to ¼ and ½ MIC to determine the growth kinetics under antibiotic stress. The study measured protease and pyocyanin production and the expression level of important quorum sensing and virulence genes (lasI/R, rhlI/R, pqsR/A, and phzA) at different growth phases. Results: Meropenem produced the most noticeable growth suppression at ½ MIC. Sub-MIC antibiotics did not completely stop growth, but caused distinct, dose-dependent changes. Azithromycin eliminated protease activity in all phases and had a biphasic effect on pyocyanin. Ciprofloxacin consistently inhibited both pyocyanin and protease in all phases. The effects of amikacin varied by phase and dose, while β-lactams markedly increased pyocyanin production during the log phase. In contrast to the plateau phase, when expression was often downregulated or unchanged, most quorum-sensing- and virulence-associated genes showed significant upregulation during the death phase under sub-MIC exposure. Conclusions: These findings indicate that sub-MIC antibiotics act as biochemical signal modulators, preserving stress-adapted sub-populations that, in late growth phases, activate quorum sensing and stress tolerance pathways. Full article
(This article belongs to the Special Issue Advancing and Standardising Antimicrobial Susceptibility and Resistance Detection Methodology)
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