Analytical Performance of Plazomicin E-strips (Ezy MIC™) Compared with Broth Micro-dilution

INTRODUCTION: Plazomicin is a novel aminoglycoside, approved by FDA in 2018 and CDSCO in 2024 for the treatment of cUTI, including pyelonephritis caused by susceptible microorganism(s): E. coli, K pneumoniae, P. mirabilis, and E. cloacae in adult patients. Plazomicin due to structural modification maintains its activity against majority of aminoglycoside modifying enzymes (AMEs). Plazomicin has shown to have good in-vitro activity against AME producing Enterobacteriaceae, CRE (MBL, OXA-48, KPC), ESBL producing Enterobacteriaceae and colistin resistant Enterobacteriaceae as well.(1,2) Antibiotic Susceptibility Testing (AST) plays an essential role in selection of targeted antibiotic therapy for the patient treatment.(3,4) OBJECTIVES: To validate multi-spectrum in-vitro activity of Plazomicin MIC strips (Ezy™ Strips) against Broth Micro Dilution (BMD) method using ATCC reference strains. MATERIALS AND METHODS: Clinical & Laboratory Standards Institute (CLSI) recommended standard QC strain E. coli ATCC 25922, Staphylococcus aureus ATCC 29213, Pseudomonas aeruginosa ATCC 27853 were studied for susceptibility testing against Plazomicin using traditional BMD method and agar diffusion method using Ezy MIC™ Strips. BMD was carried out in microtiter plate as per (CLSI) M07- 2024 using two-fold antibiotic dilution in cation-supplemented Mueller-Hinton broth (MHB). 104 CFU/ml of final inoculum was used for the testing. Ezy MIC™ strips are tested using Cation adjusted Mueller Hinton Agar (MHA). The 0.5 McFarland inoculum is swabbed on the MHA and Ezy MIC™ Strips were placed on the agar surface. For both BMD and Ezy MIC™ strips minimum inhibitory concentration (MIC) was read after 18-24 hours of incubation at suitable temperature. All studies were carried out in triplicate. RESULTS AND DISCUSSION: MIC of Plazomicin against E. coli, S. aureus, P. aeruginosa isolates using BMD method were 0.50 mcg/ml, 0.50 mcg/ml & 2.00 mcg/ml respectively. After appropriate incubation MICs were read where zone of inhibition in-form of ellipse intersects the MIC scale on the Ezy MIC™ Strip. By Ezy MIC™ Strip the MICs of Plazomicin for the same strains were found to be 0.50 mcg/ml, 0.38 mcg/ml & 2.00 mcg/ml respectively. Ezy MIC™ Strip offers advantage of direct readability of MIC value on the strip compared to BMD method where growth or no growth needs to be checked. CONCLUSION: Ezy MIC™ Strip showed comparable Plazomicin MICs with BMD method (gold standard) against standard QC strains of E. coli, S. aureus, and P. aeruginosa isolates which was in compliance with CLSI guidelines of Plazomicin.