Carbapenems are a class of highly effective antibiotics, primarily used to treat severe bacterial infections. They are typically reserved for multidrug-resistant bacterial infections. However, multidrug-resistant gram-negative bacteria exhibit various resistance mechanisms, leading to different levels of resistance to carbapenems. In this study, mutant strains of the gram-negative bacterium Klebsiella pneumoniae were analyzed for their resistance levels and mechanisms.

Evaluating the relative cell fitness on antibiotic-free medium was crucial for characterizing the mutant strains with increased carbapenem resistance compared to the clinical isolate. The Cell Growth Quantifier (CGQ) was used to produce high-resolution growth curves. Since antibiotics could not be used—commonly applied to prevent the growth of unwanted microorganisms—it was advantageous to utilize fully automated biomass measurements instead of invasive sampling, minimizing the risk of contamination.

The detailed growth curves revealed that the two mutant strains, NRZ-33224SpMut and NRZ-33224-CRISPR-rseABC, exhibited the same growth behavior but had lower growth rates compared to the clinical isolate NRZ-33224.

Antibiotic resistance among many bacteria poses a significant health threat and is the subject of extensive research. In this study, strains of the gram-negative bacterium Klebsiella pneumoniae were analyzed for their resistance levels and mechanisms. To evaluate general cell fitness, an antibiotic-free medium was used, which increases the risk of contamination due to the potential growth of unwanted microbes. Therefore, it was crucial to minimize the risk of contamination. The fully automated biomass monitoring with the Cell Growth Quantifier (CGQ) played a key role in this effort, as it eliminated the need for manual sampling, the primary source of unwanted contamination.