Antimicrobial Testing (AMT), Third Edition

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Antimicrobial Agents and Resistance".

Deadline for manuscript submissions: 15 July 2025 | Viewed by 4544

Special Issue Editor


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Guest Editor
1. Center for Surgical Infection and Biofilm, College of Medicine, Drexel University, Philadelphia, PA 19104, USA
2. Drexel School of Biomedical Engineering, Science & Health Systems, Drexel University, Philadelphia, PA 19104, USA
Interests: antimicrobial agent; resistance; bacterial pathogenesis; biofilm; host-pathogen interaction; infection control; translational medicine
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Special Issue Information

Dear Colleagues,

This Special Issue is the continuation of our previous special issues "Antimicrobial Testing (AMT)" and "Antimicrobial Testing (AMT) 2.0".

Antimicrobial susceptibility testing (AST) can be dated as early as 1924, when Dr. Fleming introduced the ditch plate technique for evaluation of antimicrobial qualities of antiseptic solutions. Since then, scientists have continued to work on advancements and evaluations of AST. Antimicrobial testing (AMT) is the world’s most widely used category of techniques, used daily by thousands of healthcare centers globally, to determine the potential effectiveness of specific antimicrobial agents on microorganisms, notably, the disk diffusion (Kirby–Bauer) method and broth dilution technique. Based on the AMT finding, it is predicted which antimicrobial will inhibit the growth of a microorganism causing a specific infection, and which antimicrobial therapy will be successful. There are lots of variations in susceptibility and resistance patterns globally, largely dependent on the regional practices of antimicrobial therapy, which not only amaze clinicians, microbiologists, and laboratory medicine scientists but challenge epidemiologists, public health personnel, and the pharmaceutical industry. As rapid diagnostic testing is pivotal in initiating specific antimicrobial therapy (and to avert development of resistance), recently, biomedical engineers and scientists have developed alternative, novel, rapid AST techniques, such as microfluidic-based optical, spectroscopy, electrochemical, piezoelectric plate sensor AST, next-generation sequencing, and many more. Additionally, automation in testing is continuously explored to save time and cost associated with in vitro testing and diagnostics.

In this Special Issue of Microorganisms, we invite original contributions (that are unpublished and not under consideration elsewhere) of research and reviews focusing on novel findings on and interpretations and significance of all different AST methods, novel strategies to determine antimicrobial resistance, unusual AST patterns of common or rare pathogens, comparison of AMT methods, in vitro synergism, antimicrobial mechanism-based studies involving AST (both phenotypic and genotypic methods), antimicrobial testing and efficacy in biofilms, novel qualitative and quantitative antimicrobial testing of natural products, synthetic molecules, and antimicrobial nanoparticles.

Dr. Suresh Joshi
Guest Editor

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Keywords

  • antibiogram
  • antibiotic susceptibility test
  • antimicrobial testing
  • bacterial resistance
  • biofilm-embedded bacteria
  • antifungal test
  • genotypic AMT
  • multidrug resistance
  • antimicrobial nanoparticle

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Related Special Issue

Published Papers (4 papers)

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Research

12 pages, 604 KiB  
Article
Exploring Metal Ions as Potential Antimicrobial Agents to Combat Future Drug Resistance in Mycoplasma bovis
by Mauida F. Hasoon Alkhallawi, Majed H. Mohammed, Farhid Hemmatzadeh and Kiro Petrovski
Microorganisms 2025, 13(1), 169; https://doi.org/10.3390/microorganisms13010169 - 15 Jan 2025
Viewed by 587
Abstract
The rise in antimicrobial resistance (AMR) in Mycoplasma bovis underscores the urgent need for alternative treatments. This study evaluated the minimal inhibitory concentrations (MICs) of four metal ions (cobalt, copper, silver, and zinc) and colloidal silver against 15 clinical M. bovis isolates, alongside [...] Read more.
The rise in antimicrobial resistance (AMR) in Mycoplasma bovis underscores the urgent need for alternative treatments. This study evaluated the minimal inhibitory concentrations (MICs) of four metal ions (cobalt, copper, silver, and zinc) and colloidal silver against 15 clinical M. bovis isolates, alongside conventional antimicrobials (florfenicol, tetracycline, tulathromycin, and tylosin). Colloidal silver demonstrated the most effective antimicrobial activity, inhibiting 81.25% of isolates at 1.5 mg/L, while silver inhibited 93.7% of isolates at concentrations above 1.5 mg/L. Copper exhibited notable efficacy, inhibiting 37.5% of isolates at 1.5 mg/L, with a small proportion responding at 0.1 mg/L. Cobalt and zinc displayed variable activity, with MIC values ranging from 0.7 to 12.5 mg/L. In contrast, conventional antimicrobials showed limited effectiveness: tetracycline inhibited 31.25% of isolates at ≥16 mg/L, tylosin inhibited 25% at 16 mg/L, and tulathromycin MICs ranged from 0.5 to 8 mg/L. Time–kill assays revealed a reduction in M. bovis viability after eight hours of exposure to silver and colloidal silver, though higher concentrations (4×–8× MIC) were required for complete eradication. These findings highlight the significant potential of colloidal silver and copper as alternatives for treating M. bovis infections and combating AMR. Further research is essential to explore their standalone and synergistic applications for therapeutic use. Full article
(This article belongs to the Special Issue Antimicrobial Testing (AMT), Third Edition)
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15 pages, 694 KiB  
Article
Subclinical Mastitis in Small-Holder Dairy Herds of Gansu Province, Northwest China: Prevalence, Bacterial Pathogens, Antimicrobial Susceptibility, and Risk Factor Analysis
by Ling Wang, Shahbaz Ul Haq, Muhammad Shoaib, Jiongjie He, Wenzhu Guo, Xiaojuan Wei and Xiaohong Zheng
Microorganisms 2024, 12(12), 2643; https://doi.org/10.3390/microorganisms12122643 - 20 Dec 2024
Viewed by 601
Abstract
This cross-sectional study assessed the prevalence, bacterial distribution, antimicrobial susceptibility, and potential risk factors associated with subclinical mastitis (SCM) in small-holder dairy herds in Gansu Province, Northwest China. Forty small-holder cow farms were randomly selected from eight cities/counties in six districts of Gansu [...] Read more.
This cross-sectional study assessed the prevalence, bacterial distribution, antimicrobial susceptibility, and potential risk factors associated with subclinical mastitis (SCM) in small-holder dairy herds in Gansu Province, Northwest China. Forty small-holder cow farms were randomly selected from eight cities/counties in six districts of Gansu Province, and a total of n = 530 lactating cows were included in this study. SCM prevalence was noted at 38.87% and 9.72% at the cow and quarter levels, respectively, based on the California Mastitis Test (CMT). The prevalence of the recovered bacterial species was noted as follows: S. agalactiae (36.02%), S. aureus (19.43%), coagulase-negative staphylococci (CNS) (16.11%), S. dysgalactiae (12.80%), E. coli (9.00%), and S. uberis (6.64%). All isolated bacteria were 100% multi-drug-resistant (MDR) except S. aureus (87.8% MDR). Antimicrobial susceptibility profiles revealed the increased resistance (>85%) of these pathogens to penicillin, streptomycin, trimethoprim–sulfamethoxazole, vancomycin, and erythromycin. However, these pathogens showed increased susceptibility to ampicillin, amoxicillin–sulbactam, ceftazidime, neomycin, kanamycin, spectinomycin, norfloxacin, ciprofloxacin, and doxycycline. The multivariate regression analysis demonstrated that old age, high parity, late lactation, lesions on teats, previous history of clinical mastitis, higher milk yield, and milking training were found to be potential risk factors (p < 0.001) associated with developing SCM in small-holder dairy cows in Gansu Province, China. These findings highlight the need for routine surveillance, antimicrobial stewardship, and effective preventive strategies to mitigate SCM in small-holder dairy production and their possible impacts, i.e., increased antimicrobial resistance and infection, on public health. Full article
(This article belongs to the Special Issue Antimicrobial Testing (AMT), Third Edition)
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15 pages, 3220 KiB  
Article
Regulatory Standard for Determining Preoperative Skin Preparation Efficacy Underreports True Dermal Bioburden in a Porcine Model
by Hannah R. Duffy, Nicholas N. Ashton, Abbey Blair, Nathanael Hooper, Porter Stulce and Dustin L. Williams
Microorganisms 2024, 12(11), 2369; https://doi.org/10.3390/microorganisms12112369 - 20 Nov 2024
Viewed by 663
Abstract
Medical device companies and regulatory bodies rely on a nondestructive bacterial sampling technique specified by the American Society for Testing and Materials (ASTM E1173-15) to test preoperative skin preparations (PSPs). Despite the widespread use of PSPs, opportunistic skin-flora pathogens remain the most significant [...] Read more.
Medical device companies and regulatory bodies rely on a nondestructive bacterial sampling technique specified by the American Society for Testing and Materials (ASTM E1173-15) to test preoperative skin preparations (PSPs). Despite the widespread use of PSPs, opportunistic skin-flora pathogens remain the most significant contributor to surgical site infections, suggesting that the ASTM testing standard may be underreporting true dermal bioburden. We hypothesized that ASTM E1173-15 may fail to capture deep skin-dwelling flora. To test this hypothesis, we applied ASTM E1173-15 and a full-thickness skin sampling technique, which we established previously through application to the backs of seven pigs (Yorkshire/Landrace hybrid) following a clinically used PSP (4% chlorhexidine gluconate). The results showed that samples quantified using the full-thickness skin method consistently cultured more bacteria than the ASTM standard, which principally targeted surface-dwelling bacteria. Following PSP, the ASTM standard yielded 1.05 ± 0.24 log10 CFU/cm2, while the full-thickness tissue method resulted in 3.24 ± 0.24 log10 CFU/cm2, more than a 2 log10 difference (p < 0.001). Immunofluorescence images corroborated the data, showing that Staphylococcus epidermidis was present in deep skin regions with or without PSP treatment. Outcomes suggested that a full-thickness sampling technique may better evaluate PSP technologies as it resolves bioburdens dwelling in deeper skin regions. Full article
(This article belongs to the Special Issue Antimicrobial Testing (AMT), Third Edition)
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11 pages, 576 KiB  
Article
The Drug Susceptibility of Non-Tuberculous Mycobacteria (NTM) in a Referral Hospital in Rome from 2018 to 2023
by Antonio Mazzarelli, Carla Nisii, Angela Cannas, Antonella Vulcano, Barbara Bartolini, Federica Turchi, Ornella Butera, Alberto Rossi, Chiara De Giuli, Chiara Massimino, Chiara Stellitano, Valentina Antonelli, Ivano Petriccione, Enrico Girardi, Gina Gualano, Fabrizio Palmieri and Carla Fontana
Microorganisms 2024, 12(8), 1615; https://doi.org/10.3390/microorganisms12081615 - 8 Aug 2024
Viewed by 1418
Abstract
Background: The treatment of non-tuberculous mycobacterial (NTM) infections is challenging because of the difficulty in obtaining phenotypic (pDST) and/or molecular (mDST) drug susceptibility testing and the need of a multi-drug regimen. Objectives: The objective was to describe the in vitro susceptibility patterns [...] Read more.
Background: The treatment of non-tuberculous mycobacterial (NTM) infections is challenging because of the difficulty in obtaining phenotypic (pDST) and/or molecular (mDST) drug susceptibility testing and the need of a multi-drug regimen. Objectives: The objective was to describe the in vitro susceptibility patterns of various NTM species through an analysis of susceptibility results obtained on isolates collected between 2018 and 2023. Methods: Species identification and mutations in rrs or rrl genes (mDST) were identified by a line probe assay, while the pDST was performed by broth microdilution and interpreted according to CLSI criteria. Results: We analysed 337 isolates of NTM belonging to 15 species/subspecies. The Mycobacterium avium complex (MAC) was the most common (62%); other species identified included M. gordonae (11%), M. kansasii (5%), the M. abscessus complex (8%), M. chelonae (6%), and M. fortuitum (2%). The results of pDST (claritromycin and amikacin) and mDST (rrl and rrs genes) on 66 NTM strains showed that while wild-type rrl and rrs occurred in 86.3% and 94% strains, respectively, the pDST showed 88% sensitivity for clarithromycin and 57.5% for amikacin. The main incongruity was observed for macrolides. Conclusions: Most NTM are likely to be susceptible to macrolides and aminoglycosides. The molecular identification of resistant genotypes is accurate and strongly recommended for optimal patient management. Full article
(This article belongs to the Special Issue Antimicrobial Testing (AMT), Third Edition)
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