Fast Antimicrobial Susceptibility Testing
By the bioMérieux Editors | Reading time: 3 min
PUBLICATION DATE: December 11, 2025
Bloodstream infections (BSIs) remain a significant public health challenge. In the United States, BSIs are among the leading causes of infection-related mortality.1,2 Globally, sepsis alone accounts for approximately 11 million deaths worldwide every year, making up 20% of global deaths.1,3 With the incidence of sepsis continuing to rise,4 there is an urgent need for diagnostic technologies that keep pace with the growing threat.
Today, antimicrobial susceptibility testing (AST) is the gold standard for guiding therapy in BSI management.5 However, conventional AST methods are often slow, taking days to deliver results.6 This delay forces clinicians to prescribe empiric, broad-spectrum antimicrobials, a practice that contributes to the overuse and misuse of antimicrobials—a leading driver of antimicrobial resistance (AMR).7
In this article, we delve into the benefits of fast AST and explore why it has the potential to bridge the critical gap in BSI and sepsis management.
Why is Antimicrobial Susceptibility Testing Important?
Antimicrobial susceptibility testing is essential in clinical care, as it guides clinicians in selecting the most effective therapy for patients with infections. By testing bacterial or fungal isolates from a patient, AST provides data that, combined with clinical information, helps determine the optimal antimicrobial agent.8 Even though therapy must begin before results are available, AST confirms whether the initial treatment is appropriate or suggests better alternatives, ensuring patients receive the best possible care.
Beyond individual treatment, AST plays a crucial role in monitoring and managing antimicrobial resistance.8 Regular analysis of resistance patterns informs evidence-based guidelines for empiric therapy, supports antimicrobial stewardship (AMS), and helps detect emerging resistance or outbreaks of multi-drug-resistant organisms. Timely and accurate AST reduces delays in effective therapy, which is linked to shorter hospital stays, lower costs, improved patient outcomes, and reduced mortality—especially in serious infections caused by resistant pathogens.9,10,11
The Future of AST
The current standard for AST is not suited to the fast-paced nature of BSIs, particularly sepsis.5,12 This has sparked the development of more advanced AST technologies, which are collectively referred to as fast AST.
Fast AST methods can be described as:
Actionable
New AST technologies deliver actionable results in hours rather than days.13 This is more timely than conventional methods, such as automated/manual broth microdilution, disk diffusion, and antimicrobial gradient methods.
Accurate
Some fast AST technologies use sensitive optical systems rather than conventional visual inspection to determine bacterial growth inhibition, which improves test accuracy.14
Standardized
Most fast AST systems rely on expert software to interpret results. Automated systems express results as quantitative minimum inhibitory concentrations (MICs), qualitative breakpoints, or both. This minimizes the uncertainty in results interpretation characterized by manual methods.5,8
Efficient
Fast AST systems often require less hands-on time to operate and include integrated software to speed the sharing of treatment-relevant data.
Advancing Stewardship. Impacting Sepsis Care.
As the landscape of bloodstream infection and sepsis management evolves, the integration of fast AST stands out as a pivotal advancement. Fast, reliable AST empowers clinicians to move beyond empiric therapy and swiftly tailor antimicrobial regimens to each patient’s unique infection profile.5,13 By delivering actionable results within a single shift, fast AST enables the care team to intervene sooner—whether that means escalating to the most effective therapy or de-escalating to minimize unnecessary antimicrobial exposure.15 This timely precision not only supports AMS but also holds the promise of improved patient outcomes and more efficient use of healthcare resources.12
Ultimately, the true impact of fast AST will be realized when laboratories, clinicians, and the entire care team work in concert to optimize workflows and ensure that diagnostic insights translate into prompt, appropriate action. As novel technologies continue to emerge, the focus must remain on reducing the time to appropriate therapy and empowering every member of the care team to act decisively.16 By advancing AMS and enhancing the timeliness of care, we can make meaningful strides in the fight against sepsis and deliver better outcomes for patients facing these life-threatening infections.
To learn more about this emerging technology, download our full fast AST guide here:
References
1. Rudd KE, Johnson SC, Agesa KM, et al. Global, regional, and national sepsis incidence and mortality, 1990-2017: analysis for the Global Burden of Disease Study. Lancet. 2020;395(10219):200-211. doi:10.1016/S0140-6736(19)32989-7
2. Rhee, Chanu et al. Incidence and Trends of Sepsis in US Hospitals Using Clinical vs Claims Data, 2009-2014.” JAMA vol. 318,13 (2017): 1241-1249. doi:10.1001/jama.2017.13836
3. Fleischmann-Struzek C, Rudd K. Challenges of assessing the burden of sepsis. Schwierigkeiten bei der Ermittlung der Sepsiskrankheitslast. Med Klin Intensivmed Notfmed. 2023;118(Suppl 2):68-74. doi:10.1007/s00063-023-01088-7
4. Owens PL, Miller MA, Barrett ML, Hensche M. Overview of Outcomes for Inpatient Stays Involving Sepsis, 2016–2021. HCUP Statistical Brief #306 | April 2024.
5. Smith KP, Kirby JE. Rapid Susceptibility Testing Methods. Clin Lab Med. 2019;39(3):333-344. doi:10.1016/j.cll.2019.04.001
6. Gajic I, Kabic J, Kekic D, et al. Antimicrobial Susceptibility Testing: A Comprehensive Review of Currently Used Methods. Antibiotics (Basel). 2022;11(4):427. Published 2022 Mar 23. doi:10.3390/antibiotics11040427
7. Modi SR, Collins JJ, Relman DA. Antibiotics and the gut microbiota. J Clin Invest. 2014;124(10):4212-4218. doi:10.1172/JCI72333
8. Reller, L. Barth et al. Antimicrobial susceptibility testing: a review of general principles and contemporary practices. Clinical infectious diseases: an official publication of the Infectious Diseases Society of America vol. 49,11 (2009): 1749-55. doi:10.1086/647952
9. Evans RN, Pike K, Rogers CA, et al. Modifiable healthcare factors affecting 28-day survival in bloodstream infection: a prospective cohort study. BMC Infect Dis. 2020;20(1):545. Published 2020 Jul 25. doi:10.1186/s12879-020-05262-6
10. Bonine NG, Berger A, Altincatal A, et al. Impact of Delayed Appropriate Antibiotic Therapy on Patient Outcomes by Antibiotic Resistance Status From Serious Gram-negative Bacterial Infections. Am J Med Sci. 2019;357(2):103-110. doi:10.1016/j.amjms.2018.11.009
11. Perez KK, Olsen RJ, Musick WL, et al. Integrating rapid diagnostics and antimicrobial stewardship improves outcomes in patients with antibiotic-resistant Gram-negative bacteremia. J Infect. 2014;69(3):216-225. doi:10.1016/j.jinf.2014.05.005
12. Garrett E, et al. Recent advances in direct blood culture phenotypic antimicrobial susceptibility testing. Clinical Microbiology Newsletter. vol. 44, 23 (2022):209-216. doi: 10.1016/j.clinmicnews.2022.11.005.
13. Banerjee R, et al. Rapid antimicrobial susceptibility testing methods for blood cultures and their clinical impact. Front Med. 2021; 8:635831. doi:10.3389/fmed.2021.635831.
14. Brown C, et al. Automated, Cost-Effective Optical System for Accelerated Antimicrobial Susceptibility Testing (AST) Using Deep Learning. ACS Photonics. 2020;7(9):2527–2538.
15. Anton-Vazquez V, Suarez C, Planche T. Impact of rapid susceptibility testing on antimicrobial therapy and clinical outcomes in Gram-negative bloodstream infections. J Antimicrob Chemother. 2022;77(3):771-781. doi:10.1093/jac/dkab449
16. MacVane SH, Dwivedi HP. Evaluating the impact of rapid antimicrobial susceptibility testing for bloodstream infections: a review of actionability, antibiotic use and patient outcome metrics. J Antimicrob Chemother. 2024;79(12 Suppl 2):i13-i25. doi:10.1093/jac/dkae282
