Assessment of CHROMagar Culture Media for the Rapid Detection of Antibiotic- Resistant Strains (Staphylococcus Aureus, Enterococcus Sp., and Enterobacteriaceae) under Suboptimal Storage

Antimicrobial resistance (AMR) is a major global public health threat, potentially affecting up to 82% of bloodstream infection cases depending on the country. Rapid detection of multidrug-resistant bacteria is essential for effective management. Among the most frequently reported priority pathogens are Escherichia coli, Klebsiella pneumoniae, methicillin-resistant Staphylococcus aureus, Streptococcus pneumoniae, and Salmonella spp., for which early and targeted identification is crucial to guide appropriate treatment.
This study assesses the performance of chromogenic media in detecting and presumptively identifying methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and beta-lactam-resistant Enterobacteriaceae (ESBL), including carbapenem-resistant Enterobacteriaceae (CPE). The CHROMagar MRSA, VRE, ESBL, and mSuperCARBA media were evaluated using known resistant strains and American Type
Culture Collection (ATCC) reference strains, comprising 3 strains of Staphylococcus spp., 10 strains of Enterobacteriaceae, and 4 strains of Enterococcus spp. Colony coloration were interpreted based on the manufacturer's guidelines.
Under optimal conditions, the ESBL, mSuperCARBA, and VRE media demonstrated 100% sensitivity and specificity for detection, while the MRSA medium exhibited 100% sensitivity but only 79% specificity. Under suboptimal conditions (storage at 20 degrees Celsius (°C) and 35°C in darkness, and 20°C under light), the ESBL, mSuperCARBA, and MRSA media maintained 100% sensitivity, though VRE sensitivity dropped to 78% under 20°C with light exposure. Specificity for ESBL, mSuperCARBA, and VRE remained at 100% in these conditions, while MRSA specificity decreased to 52%.
In summary, the tested CHROMagar media effectively detect resistant bacteria with high sensitivity and specificity under optimal conditions. However, MRSA and VRE media exhibit variability in performance under suboptimal storage conditions.