Nitrate Reductase Assay for Rapid Determination of Methicillin-Resistant Staphylococcus aureus Clinical Isolates

OBJECTIVE

To evaluate the performance of nitrate reductase assay (NRA), a rapid, colorimetric method for the determination of methicillin resistance in Staphylococcus aureus isolates obtained from the culture collection of the Akdeniz University Hospital Central Laboratory, Antalya, Türkiye.

MATERIALS AND METHODS

Identification for all 290 S aureus isolates at the species level was performed via matrix-assisted laser desorption/ionization-time of flight. Isolates were tested with NRA for methicillin resistance. The cefoxitin broth microdilution (BMD) method recommended by the Clinical and Laboratory Standards Institute was used as the reference method in the study. S aureus ATCC 29213 and S aureus ATCC 43300 strains were used for quality control.

RESULTS

According to Food and Drug Administration criteria, the category agreement between NRA and BMD was found to be 100%. The essential agreement between both methods was determined to be 96.20%. There is no minor, major, or extremely major discrepancy between both methods.

CONCLUSION

The results show that NRA is a rapid, practical, and reliable colorimetric method for detecting MRSA.

A New Colorimetric Method for Rapid Detection of Antibiotic Resistance in Escherichia coli Isolates

Background: The quick diagnosis and early initiation of antibiotic therapy in bacteria-induced infections is of paramount importance. Accordingly, the rapid identification of the causative agent, the short-term results of antibiotic sensitivity, the selection and use of right antibiotics for treatment further highlights the significance of this issue. Objectives: This study aimed to develop a new susceptibility testing method to provide rapid results in Escherichia coli clinical isolates and report the antibiotic susceptibility test results to clinicians in a short period. Methods: In the study, one hundred and ten E. coli clinical isolates were tested. In this regard, antibiotics recommended by the "Clinical and Laboratory Standards Institute (CLSI)" for testing the sensitivity of E. coli isolates, including amoxicillin-clavulanate, cefixime, ceftriaxone, ertapenem, ciprofloxacin, gentamicin, trimethoprim-sulfamethoxazole, and nitrofurantoin were tested. For quality control, E. coli ATCC25922, E. coli ATCC35218, Staphylococcus aureus ATCC29213, and E. coli 13846NTCC strains were used. The broth microdilution method recommended by CLSI was used as the reference method. Minimum inhibitory concentration values were determined, and antimicrobial susceptibilities were then determined according to the “European Committee on Antimicrobial Susceptibility Testing (EUCAST)” criteria. In the next phase, the results of the resazurin microplate method (RMM) were compared. Results: The comparison of the RMM developed in the present study with the reference method revealed that the calculated essential agreement ratios for eight antibiotics varied from 82.72 to 100%, and the categorical agreement values ranged from 95.45 to100%. Conclusions: According to the findings, the RMM results were highly in agreement with the results of the reference method. RMM allows the detection of antibiotic susceptibility quickly (e.g., within 5 hours) as such it is preferred, especially for laboratories with limited facilities. However, further multi-center studies are recommended to use this method in routine laboratories.