Expert Insight: Investigating traditional and modern approaches to antimicrobial susceptibility testing

Explore ways to improve time to result in critical pathways such as sepsis

14 Dec 2020

Dr. Rafael Canton, Head of the Clinical Microbiology Department at the University Hospital Ramón y Cajal
Dr. Rafael Canton, Head of the Clinical Microbiology Department at the University Hospital Ramón y Cajal

Looking for some true insight into the antimicrobial susceptibility testing methodologies of today and tomorrow? Both clinical and hospital laboratories use antimicrobial susceptibility testing to investigate possible drug resistance in common pathogens and to identify which antimicrobial agents are effective against certain infections.

In this on-demand SelectScience webinar, Dr. Rafael Canton, Head of the Clinical Microbiology Department at the University Hospital Ramón y Cajal and Associated Professor of Clinical Microbiology in the School of Pharmacy at Complutense University of Madrid, explores why rapid antimicrobial susceptibility testing is so important at a time when antibiotic resistance is growing into one of the biggest challenges the world faces. Here, Dr. Canton provides ways to improve time to result in critical pathways such as sepsis, considering current trusted methods along with the upcoming technology and the pros and cons of adoption.

Read on for highlights from the webinar’s Q&A session or register now to watch the webinar on demand.

Q: With rapid antibiotic susceptibility testing (AST) being implemented in labs, how do you see it becoming part of the routine workflow?

RC: With the system that we are investigating, you would typically use one to three isolates, but not in a way we usually perform antibiotic susceptibility testing. In a standard workflow, we perform a lot of antibiotic susceptibility testing, so we need automated methods. This new system will do this, so it will most likely become part of the routine workflow with ease.

Q: What do you see as the most important sample type to utilize with rapid AST?

RC: We use rapid antibiotic susceptibility testing in blood culture because it's a microorganism that came from invasive infection, and from a sepsis patient that had this bacteremia. If we prove that it is useful for blood culture, why not expand to one that can be used for respiratory infection? In the future, we are looking to implement urine in our clinical laboratory.

Q: With the current COVID situation, do you believe it's more important to implement new rapid methods? Will labs be able to afford these new methods?

RC: Right now, all the efforts of laboratories are focused on COVID diagnosis, so they don't have time to do other things. Rapid testing methods would benefit labs, but we have very few rapid testing methods for antimicrobial susceptibility testing. We expect that the COVID situation will end very soon and we will return to normality in our labs.

Q: What type of susceptibility tests do you consider more appropriate for chemical labs within developing countries?

RC: In developing countries, the most useful ones would be disk diffusion, but it can also be used in more developed countries. This method can be used in a normal way with traditional overnight culture. Now we have protocols, particularly with blood culture, where you can do this as rapid antimicrobial susceptibility testing. You can read the disk diffusion in 6-8 hours which is an improvement.

Q: As it was World Sepsis Day this week, and with the increasing visibility of worldwide deaths due to sepsis, how do you believe the management of sepsis cases will change in the future?

RC: One of the first steps is to rapidly diagnose sepsis, and we have biochemical tests to demonstrate that. Once we have diagnosed a sepsis patient and the sepsis is related to a microorganism, we must identify which microorganism and perform antimicrobial susceptibility testing. For some of the tools that we have introduced in the lab, for instance, MALDI-TOF for identification in blood culture, this rapid way of doing this antimicrobial susceptibility testing has demonstrated an improvement in the patients' survival rate.

Q: From the new technologies you've presented, which one is likely to win the already crowded AST market?

RC: We have different systems and flow cytometry is one of them. We also have calorimetry, and we have cantilevers. The one that will win in the crowded AST market is the one that will be automatized in protocols. If you have a system that has random access to the microorganism, performing automated antibiotic susceptibility testing will be a win in the future. For instance, if we can automate flow cytometry, this would be a system that will win. If we have a cantilever or another microscopy-like system doing this rapid antibiotic susceptibility testing, this will be the one that will win.

Q: Are there any drawbacks in real-time microscopic methods since it seems to offer a lot of data?

RC: With the techniques that we are using now, the automatic system for instance, we can measure the presence or absence of growth. With some systems, we can measure the course of how the microorganism is growing during this period, even if it is an 18-hour period. Most of this information is discharged from the system because you need the Minimal Inhibitory Concentration (MIC).

You can obtain the MIC and interpretation with the new microscopy system. However, you may obtain more information regarding this way of growing the microorganism, specifically the course. Just by analyzing the course regarding these microorganisms present in the machines, you can measure these different growths to recognize subpopulations that may have different antibiotic susceptibility testing results. For instance, you can measure these different growths to recognize the subpopulation that is resistant or tolerant microorganisms.

Q: Has there been a secondary bacterial infection most associated with global COVID mortalities, either in humans or primates or in animal modeling studies as zoonotic COVID- like viruses?

RC: The superinfection problem with COVID patients has been studied but we don't have a lot of data yet. We have some series that appear. This bacterial infection in the COVID patient is infrequent. They are present around 20% of the time, depending on the risk of the patient. If the patient was in ward or an intensive care unit, it's important to implement rapid antimicrobial susceptibility testing and to have data from the rapid implementation of antimicrobial therapy.

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