Ceftazidime-Avibactam plus aztreonam synergistic combination tested against carbapenem-resistant Enterobacterales characterized phenotypically and genotypically: a glimmer of hope

BACKGROUND: Carbapenemase-producing Enterobacterales (CPE) show rapid global dissemination and pose a significant therapeutic challenge. This study aimed to characterize carbapenemase-producing Klebsiella spp. and Escherichia coli (E. coli) phenotypically and genotypically and evaluate the effect of ceftazidime/ avibactam plus aztreonam combination. METHODS: A total of 219 Klebsiella species and 390 E. coli strains were isolated from clinical samples, in which 80 Klebsiella spp. and 20 E coli isolates were resistant to tested carbapenems (imipenem, ertapenem, meropenem) by disk diffusion/broth dilution method and Vitek-2 compact system. MASTDISCS Combi Carba plus discs and real time PCR were used to determine type of carbapenemase phenotypically and genotypically, respectively. Interestingly, the synergistic effect between ceftazidime-avibactam (E-test) and aztreonam (disc) was tested against the CPE isolates. RESULTS: Out of the carbapenem-resistant isolates, 76.25% Klebsiella spp. isolates were extensively drug-resistant (XDR) while 18.75% were pan drug-resistant (PDR), and 5% were multidrug-resistant (MDR). Regarding E. coli, 5% were PDR, 20% were MDR and 75% were XDR. More than one carbapenemase gene was detected in 99% of the isolates. In comparison between MAST-Carba plus discs and PCR results, sensitivity and specificity were (85.42–97.92%) in Klebsiella spp., and (69.64–100%) in E. coli, respectively. Moreover, a strong association was detected between both test results among Klebsiella spp. (p < 0.001) and E. coli (p = 0.012) isolates. Finally, ceftazidime-avibactam and aztreonam combination showed a synergistic effect in 98.8% of Klebsiella spp. and 95% of E coli. All 16 PDR isolates showed synergy. CONCLUSION: This synergistic effect spots the light on new therapeutics for XDR and PDR CPE.