Version 1: Analysis of a simple disk diffusion method to evaluate Ceftazidime-avibactam/Aztreonam combination synergism against NDM clinical isolates.

Treatment with Ceftazidime avibactam/Aztreonam combination may offer a clinical benefit in patients suffering with Multidrug resistant bacterial infection. The present study aimed to detect genes encoding carbapenem resistance in clinical strains and to evaluate the efficacy of ceftazidime-avibactam/aztreonam combination against carbapenemase co-producers. A Cross-sectional research was done on 62 Carbapenem resistant Gram negative isolates obtained from clinical samples collected during October 2022 to January 2024. Ceftazidime/avibactam-Aztreonam Synergy against 55 carbapenemase producers (NDM, IMP, VIM & OXA-48) was determined by disk diffusion method. Data analysis was done by frequencies and percentages. Ceftazidime-avibactam/Aztreonam synergy was identified against 25(64.10%) out of 39 isolates exhibiting NDM gene, 7(77.78%) out of 9 isolates (Co-producers of NDM and OXA-48 genes), 2(50%) out of 4 isolates (Co producers of NDM and VIM carbapenemase gene) and a single isolate ((33.33%) out of 3 isolates with NDM, VIM and OXA-48 gene. A wide zone of 3-23 mm diameter was observed for Enterobacterales and 13-14mm for Pseudomonas aeruginosa with Ceftazidime -avibactam/Aztreonam combination in relative to Ceftazidime -avibactam and Aztreonam disk tested alone. The present study showed in-vitro effectiveness of Ceftazidime -avibactam/Aztreonam combination against 63.64% carbapenem resistant isolates studied. Disc diffusion method requires less technical expertise, and the test result aid to identify the true clinical synergy by observing the enhancement of the zone diameter that exceeds the susceptibility breakpoint for Aztreonam.