Synergistic effect of ceftazidime/avicarbam combined with aztreonam against carbapenem-resistant Klebsiella pneumoniae isolates

Objective To explore the synergistic effect of ceftazidime/avicarbam combined with aztreonam against carbapenem-resistant isolates of Klebsiella pneumoniae (CRKP). Methods We collected 10 clinical isolates of CRKP from our hospital and determined the minimal inhibitory concentrations of the commonly used antibiotics in these isolates using agar plate double-dilution method. The carbapenemase genes and extended-spectrum β-lactamase genes of the bacteria were amplified by PCR, and the expression of carbapenemase genes was detected by RT-PCR. The bacterial genotypes were analyzed with multilocus sequence typing. The synergistic effect of ceftazidime/avicarbam combined with aztreonam against these CRKP isolates was determined using the checkerboard method. Results The 10 CRKP isolates were all sensitive to tigecycline but highly resistant to all the other antibiotics tested. The β-lactamase genes (NDM, CTX-M and SHV) were widely distributed in these isolates, and the strains with a high resistance to carbapenem also had high expression levels of carbapenemase genes (r=0.805, P=0.029). Four distinct ST genotypes were identified among the CRKP strains, and the genotype ST11 had the highest epidemic potential; NDM gene was present in the strains of 3 different ST genotypes. Ceftazidime/avicarbam combined with aztreonam showed a synergistic inhibitory effect in 7 CRKP strains and produced irrelevant effects in the other 3 strains. Conclusion The high resistance of CRKP strains can be attributed to the resistance genes they carry, and the combination of ceftazidime/avicarbam and aztreonam can produce a strong synergistic inhibitory effect in these strains.carbapenem-