The Case for Chromogenic Agar
in the Age of MALDI-TOF MS
Matrix-Assisted Laser Desorption Ionization – Time of Flight Mass Spectrometry (MALDI-TOF MS) has revolutionized clinical microbiology, providing rapid and highly specific bacterial identification. However, despite its advantages, chromogenic agar remains a vital tool in certain workflows. In this article, we explore where chromogenic agar still holds value in microbiology laboratories and how it complements MALDI-TOF MS.
MALDI-TOF MS and Chromogenic Agar: Workflow Considerations
MALDI-TOF MS allows clinical laboratories to obtain bacterial identification from isolates within minutes, significantly outperforming traditional biochemical assays. Its high specificity and cost-effectiveness per identification make it a powerful tool, though the upfront investment in equipment and maintenance can be substantial.
However, workflow efficiency is a critical consideration. MALDI-TOF MS identification follows a batch process—technologists work up cultures, select colonies, and prepare a plate for testing. While this approach optimizes batch efficiency, it may delay results depending on lab protocols.
Chromogenic agar, on the other hand, enables a more immediate visual identification of pathogens. The distinct color changes in specific media allow for faster presumptive identification. For example, chromogenic media designed for MRSA detection can provide preliminary results without the need for additional tests. While more complex chromogenic agars for urine cultures may require simple confirmatory tests, they streamline the workflow by reducing the number of steps needed for pathogen identification.
The Role of Chromogenic Agar in Pathogen Screening
Chromogenic agar is widely used for pathogen screening, particularly for organisms like MRSA, VRE, and Candida auris. These organisms often require rapid identification for infection control and treatment decisions. Studies published in Letters in Applied Microbiology and presentations at ASM have demonstrated:
- Improved sensitivity and specificity for targeted pathogens
- Reduced turnaround time (TAT)
- Cost efficiency in high-throughput screening settings
- Ease of interpretation, allowing technologists to work more efficiently
Beyond clinical applications, chromogenic agar plays a role in public health settings, including food safety monitoring and outbreak detection.
Urine Cultures: A Case for Chromogenic Agar
One of the most notable applications of chromogenic agar is in urine culture workflows. Processing high volumes of urine cultures is labor-intensive, and chromogenic agar can help streamline these processes.
Several chromogenic media are commercially available for urine cultures, including:
- Orientation Agar (CHROMagar)
- UriSelect 4 (Bio-Rad)
- CHROMID CPS Elite (bioMérieux)
- Brilliance UTI Clarity (Oxoid)
These agars use multiple chromogens to differentiate common urinary pathogens, facilitating faster reporting with biochemical confirmation where needed.
A Canadian study analyzing 310 urine cultures across four different chromogenic media found that workup time was reduced by 50% compared to traditional culture methods. This translated to 80 labor hours saved per month—a significant reduction in manual workload. Given that clinical microbiology technologists earn $36-$60 per hour (including benefits), this equates to annual labor savings of $34,560-$57,600.
Further research, including a study by Manickam et al., demonstrated a 28% reduction in workload when incorporating chromogenic agar into urine culture workflows. Additional findings suggest that chromogenic agar can accelerate Candida species detection by 24-48 hours, improving turnaround times for fungal infections.
Enter the Complementary Approach
While MALDI-TOF MS remains a gold standard in microbial identification, chromogenic agar continues to provide workflow advantages in key applications. For high-throughput screening, pathogen detection, and urine culture processing, chromogenic agar enables faster presumptive identification and improved efficiency.
In many cases, these two technologies work best together—with chromogenic agar serving as a front-line tool for rapid identification and MALDI-TOF MS providing confirmatory testing when needed.
As laboratories continue to balance cost, efficiency, and accuracy, chromogenic agar remains a valuable asset in modern clinical microbiology.
For an in-depth review of chromogenic culture media, check out this comprehensive review published in CMR.
Support for Pathogen Identification Assays
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