The in vitro synergistic and antibiofilm activity of Ceftazidime/avibactam against Achromobacter species recovered from respiratory samples of cystic fibrosis patients

Achromobacter spp. may form biofilm in patients' respiratory tracts and cause serious infections. This research examined the bactericidal and synergistic effects of ceftazidime/avibactam (CZA) alone and in combination with different antibiotics against Achromobacter spp.

MICs of 52 Achromobacter spp. were determined by broth microdilution. In-vitro time-kill curve experiments assessed CZA's bactericidal and synergistic properties alone and in combination with other antibiotics. Moreover, the antibiofilm activity of CZA alone or in combination with the antibiotics was assessed with using microplate method.

Based on MIC₉₀ values, CZA exhibited four times greater in-vitro activity against tested strains than ceftazidime. The most effective agent was meropenem, with a 92% susceptibility level on the tested strains. On the other hand, ciprofloxacin was found to be bactericidal at both 1 × and 4xMIC concentrations. CZA, chloramphenicol and meropenem were observed to have bactericidal effects alone at 4xMIC concentrations against the tested isolates. CZA + CS and CZA + MEM showed synergy in three out of five and two out of five strains tested at 1xMIC, respectively. Furthermore, the pairing of CZA with colistin, CZA with meropenem and CZA with ciprofloxacin exhibited a synergistic impact at 4xMIC. Moreover, combination therapy CZA with the tested antibiotics showed reduced biofilm formation in a concentration-dependent manner at 24 h.

The outcomes of this research also suggest that CZA plus colistin, meropenem, or ciprofloxacin were more productive against Achromobacter strains. To our knowledge, this is the first article to evaluate the synergistic and antibiofilm activities of CZA alone or in combination with different agents against Achromobacter species.