Combined dual β-lactams and diazabicyclooctane β-lactamase inhibitor is highly effective against Mycobacterium abscessus species in vitro

Objective

Mycobacterium abscessus pulmonary disease is a refractory infectious disease. Developing an effective treatment is urgent as the number of patients infected with M. abscessus species (MABS) is increasing worldwide. We previously reported that nacubactam, a diazabicyclooctane (DBO) β-lactamase inhibitor, could inhibit MABS β-lactamase. Few reports have indicated that dual β-lactams are effective with a DBO β-lactamase inhibitor against MABS. The objective of this study was to determine which dual β-lactams have high antibacterial activity against MABS in the presence and absence of nacubactam.

Methods

Antimicrobial susceptibility tests were conducted through a checkerboard assay of 27 β-lactams using the broth microdilution method for three subspecies-type strains and 20 clinical isolates of MABS. The number of intracellular and extracellular bacteria was measured using human macrophages infected with M. abscessus treated with effective combinations confirmed in susceptibility tests.

Results

In antimicrobial susceptibility tests, 91 combinations of dual β-lactams with nacubactam exhibited synergistic effects on M. abscessus JCM13569. Among them, the combination of cefazolin, cefotiam, cefoxitin, or cefuroxime with imipenem and nacubactam exhibited highly synergistic effects, resulting in low MICs against MABS clinical isolates. Without nacubactam, the combination of imipenem and cefoxitin showed the lowest MIC. In experiments using human macrophages infected with M. abscessus, these dual β-lactam combinations reduced the number of intracellular and extracellular bacteria compared with those of single β-lactams.

Conclusions

The combination of cefazolin, cefotiam, cefoxitin, or cefuroxime with imipenem and nacubactam was highly effective against MABS. Without nacubactam, the combination of cefoxitin and imipenem was effective.