​​​​The APHL-ASM Antimicrobial Resistance Laboratory Workgroup

The APHL-ASM Antimicrobial Resistance (AR) Laboratory Workgroup is a collaboration between public health and clinical laboratories whose goal is to identify and develop initiatives to improve detection and reporting of AR while fostering the relationship between clinical and public health laboratories. Members include representatives from public health laboratories, clinical microbiologists and CDC. ​​

Carbapenem Resistant Organisms

Carbapenem-resistant organisms (CROs) are a major concern for patients in healthcare facilities. Some pathogens in this family are resistant to nearly all antibiotics, leaving more toxic or less effective treatment options. The CDC's 2019 AR Threats Report categorizes carbapenem-resistant Enterobacterales and carbapenem-resistant Acinetobacter as urgent threats, while also categorizing multidrug-resistant Pseudomonas aeruginosa as a serious threat.​

Clinical Breakpoints

The interpretation of antimicrobial susceptibility testing (AST) results is done via the assignment of breakpoints, which divides results (minimum inhibitory concentrations (MIC) or disk diffusion zone of growth inhibition values), into categories that correlate with the probability of clinical outcomes. Breakpoints are revised to ensure patient care and safety and to limit and reduce the spread of antimicrobial resistance.​ Failure to use correct breakpoints during AST can result in incorrect interpretation of results, allowing for inappropriate treatment course, poor patient outcomes and continued spread of resistant infections.​​​

The Clinical and Laboratory Standards Institute (CLSI) revised the carbapenem breakpoints for Enterobacterales in 2010, decreasing the thresholds to avoid mischaracterizing potentially resistant ​Enterobacterales as susceptible. However, adoption of the updated MIC breakpoints has proved challenging for clinical microbiology laboratories that use commercial MIC susceptibility testing systems due to verification study that must be completed according to CLIA requirements. 

The CRO Breakpoint Implementation Toolkit

The AR Laboratory Workgroup identified providing assistance to laboratories in the implementation of updated carbapenem susceptibility breakpoints as an important area of work. To that end they developed a toolkit laboratories can utilize to guide them through the verification study needed to implement the updated breakpoints. The first iteration of the toolkit focuses on updating carbapenem​ breakpoints for Enterobacterales. Future iterations will expand to include additional drug-bug combinations. The toolkit components include:

​Learn More​​

For more information about the AR​ Laboratory Workgroup and the CRO Breakpoint Implementation Toolkit, please contact the APHL staff liaison for the workgroup, Nikki Marchan.