MDRO Testing in a Shifting Regulatory Environment: What Recent Updates Mean for the Laboratory

How updated CLSI, EUCAST and UKHSA requirements affect testing, media and reporting. 

In this article, you’ll learn:

• How MDRO testing regulation is converging across the USA, EU and UK

• Why Clostridioides difficile and Staphylococcus aureus remain priority organisms for surveillance

• Which broader MDROs, including ESBL and CRE producing organisms and VRE, are drawing increased regulatory attention

• Why standardized AST methods and controlled media remain central to defensible results

• How molecular methods, culture and whole-genome sequencing fit together rather than replace one another

• What these changes mean for laboratory testing infrastructure and quality systems

Recent regulatory and guideline updates across the USA, EU and UK are pushing MDRO testing toward greater standardization, stronger surveillance, and microbiology results that support infection prevention, stewardship and treatment decision-making. For laboratories, this shift means that the consistency, traceability, and reliability of the media and methods behind every result now carry direct regulatory and clinical weight.

The shift in emphasis is consistent across all three regions. Regulators are treating antimicrobial resistance less as a series of isolated, organism-by-organism problems, and more as a single system connecting microbiology, infection prevention and control, and antimicrobial stewardship to measurable patient outcomes.

Antimicrobial susceptibility testing (AST) sits at the center of that system. AST depends on standardized methods and controlled inputs, including media, quality controls, and documented procedures, to produce results that laboratories, clinicians, and regulators can rely on.

How is AST regulation becoming more standardized across the US, EU and UK? 

AST is becoming more tightly controlled and more standardized. In the USA, the Food and Drug Administration (FDA) continues to support national efforts to address antimicrobial resistance, while the Clinical and Laboratory Standards Institute (CLSI) refines breakpoint criteria (CLSI M100, 2026 edition), so that laboratories interpret resistance consistently.

In the EU, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) has updated its breakpoint tables (v16.1, 2026), with refinements for anaerobes and for rapid AST methods. In the UK, antimicrobial resistance remains a national public health priority, with the UK Health Security Agency (UKHSA) and National Health Service (NHS) supporting surveillance, reporting and antimicrobial stewardship programmes that link microbiology data to infection prevention and healthcare performance. These bodies have strengthened mandatory reporting of healthcare-associated infections, linking microbiology data directly to hospital performance and to stewardship targets.

Globally, the World Health Organization continues to report high resistance rates of antimicrobial resistance through its Global Antimicrobial Resistance and Use Surveillance System (GLASS-AMR), reinforcing the case for reliable, standardized testing wherever samples are processed. The practical message for the laboratory is consistent across every jurisdiction: alignment with recognized standards is becoming a baseline expectation across many healthcare and testing laboratories, and the quality of the inputs, including media, controls, and method validation, increasingly determines whether a result is defensible.

“The regulatory direction is clear: MDRO testing needs to be comparable, reproducible and traceable across laboratories. Recognized methods and interpretive criteria are essential, but they depend on controlled inputs, including media, quality controls and documented workflows, to support defensible results.”

Yoggya De Silva, Product Manager — Culture Media Life Sciences Portfolio, AnalytiChem Group

Why do clostridioides difficile and Staphylococcus aureus remain priority organisms?

•  Clostridioides difficile

C. difficile infection remains a key healthcare-associated infection, driven largely by antibiotic exposure. Recent guidance is firm that diagnosis must combine clinical symptoms with laboratory confirmation, rather than relying on a single test in isolation.

Current guidance generally recommends a multistep testing algorithm. An initial, sensitive screen (glutamate dehydrogenase (GDH), or a nucleic acid amplification test (NAAT)) is followed by toxin detection (enzyme immunoassay) to confirm active infection. Used together, these steps reduce the overdiagnosis that occurs when a laboratory detects colonization rather than a genuine toxin-producing infection.

Laboratories sourcing rapid assays for this workflow can access the Clostridium difficile QUIK CHEK™ combination test and the Clostridium difficile Tox B™ Test through AnalytiChem’s third-party marketplace listings.

From a laboratory perspective, this reinforces the continued need for reliable routine culture workflows to recover isolates for reference and epidemiological purposes, and for dependable environmental monitoring media to detect contamination and support infection prevention efforts on the ward.

• Staphylococcus aureus (including MRSA)

Methicillin-resistant Staphylococcus aureus (MRSA) remains a critical pathogen in bloodstream infections and in hospital transmission. The regulatory and surveillance themes here are well established: continued mandatory surveillance (through UKHSA, and the US Centers for Disease Control and Prevention (CDC)), standardized detection methods (EUCAST-specified detection of the mecA or mecC gene, or cefoxitin as the surrogate marker for methicillin resistance), and interpretation aligned with CLSI and EUCAST standards.

Although MRSA rates have improved in several regions, that progress depends on consistent detection and reporting. It’s precisely because the trend is encouraging that the underlying testing must remain rigorous.

What broader MDROs are drawing increased regulatory attention?

While C. difficile and S. aureus attract sustained attention, the most significant global concern now sits with resistant Gram-negative organisms, complemented by ongoing Gram-positive challenges.

The principal Gram-negative concerns are extended-spectrum beta-lactamase (ESBL) producing Enterobacterales and carbapenem-resistant Enterobacterales (CRE), both of which are associated with limited treatment options and rising incidence in surveillance data. Alongside these, vancomycin-resistant enterococci (VRE) represent the key Gram-positive resistance of concern. Enterococci are Gram-positive cocci; they are grouped here as MDROs of interest, not as Gram-negative organisms.

Regulatory focus in this area centers on updated AST breakpoints from CLSI and EUCAST, increased active screening (for example, rectal swabs for CRE detection), and improved completeness of reporting and surveillance.

Which core microbiology workflows support MDRO testing?

The regulatory backbone of MDRO testing continues to rest on two well-characterized AST methods: disk diffusion (the Kirby-Bauer method) and broth microdilution for minimum inhibitory concentration (MIC) determination. Both depend on standardized media, mainly Mueller-Hinton Agar and cation-adjusted Mueller-Hinton Broth, in which controlled calcium and magnesium levels are essential for reproducible, comparable results. These media are specified within CLSI and EUCAST methodologies because they underpin reproducible and comparable interpretation of susceptibility results.

Where bacterial load is low, as is often the case in MDRO screening, enrichment broths improve sensitivity. Commonly used options include Tryptic Soy Broth, Brain Heart Infusion Broth, Bile Esculin Azide Broth, and MacConkey Broth, with selective agents added according to the screening question being asked.

This is where pre-prepared, quality-controlled media earns its place. Ready-to-use Mueller-Hinton plates and broths support AST workflows, Tryptic Soy Agar plates serve general microbiology, and contact and settle plates underpin environmental monitoring.

Redipor® ready-to-use media products are designed to support these requirements: reducing preparation variability, improving batch-to-batch consistency, and supporting the traceability and audit readiness that Good Manufacturing Practice and modern regulatory expectations demand. In a landscape where a result must be defensible, removing avoidable variability from media preparation is one of the most direct contributions a laboratory can make to data quality.

“Ready-to-use culture media should be viewed as part of a controlled microbiology workflow. When appropriately selected, qualified and used within documented procedures, they can help support consistency, reduce avoidable preparation variability and strengthen traceability.”

Yoggya De Silva, Product Manager — Culture Media Life Sciences Portfolio, AnalytiChem Group

A recurring misconception is that molecular methods will simply displace culture. The clearer trend is integration. Molecular methods, such as polymerase chain reaction (PCR), offer rapid detection; culture methods remain essential for susceptibility testing and isolate recovery. In some reference and public-health laboratory settings, whole-genome sequencing is increasingly being used to characterize resistance mechanisms and support epidemiological investigations. Each has a defined role, and regulators expect the combined output to be clinically relevant, standardized, and interpretable across systems.

What does this mean for laboratories and healthcare systems?

Standardization is now essential, which makes alignment with CLSI and EUCAST rationale a baseline expectation rather than a differentiator. The scientific rationale behind evolving AST breakpoints and interpretive criteria is increasingly transparent through guidance and supporting rationale documents published by these organisations.

Surveillance is becoming more data-driven, so both testing volume and completeness matter. Infection prevention and control is tightly coupled to diagnostics, meaning faster detection translates directly into better isolation and outbreak management. Antimicrobial stewardship depends on reliable microbiology, because accurate AST results shape real treatment decisions.

MDRO testing is evolving from a laboratory-focused activity into a core component of integrated healthcare decision-making. Across the US, EU, and UK, the direction is the same: stronger standardization, more complete surveillance, and diagnostics that are fast enough — and reliable enough — to change what happens on the ward.

What it takes to keep results defensible

That direction plays out differently across the organisms discussed here. For Clostridioides difficile, it means a multistep algorithm that avoids overdiagnosis while still catching genuine infection; for Staphylococcus aureus and MRSA, it means sustained surveillance and standardized detection even as rates improve in several regions. For the broader group of ESBL and CRE producing organisms and VRE, it means active screening and more complete reporting to track incidence that is still rising in many settings.

What connects it all is the reliability of what happens behind the result: AST methods that follow CLSI and EUCAST specifications, enrichment strategies suited to low bacterial load, and culture media controlled tightly enough to produce the same answer in any laboratory that runs the test. Molecular methods and whole-genome sequencing add speed and surveillance depth, but they extend this foundation rather than replace it.

Laboratories that treat media quality, method validation, and documented procedure as inseparable from the testing itself are the ones best placed to meet not only today’s expectations, but the tighter standards that are clearly on the way. For laboratories reviewing AST and enrichment workflows against these updated expectations, AnalytiChem’s Redipor® ready-to-use media products are designed to support consistency, traceability and workflow standardisation across routine microbiology applications.