A. catalase-negative

Being "catalase-negative" means that a particular bacterium does not produce the enzyme catalase. Catalase helps bacteria break down hydrogen peroxide, a substance that can damage cells, into harmless water and oxygen. Most bacteria have this enzyme to protect themselves from oxidative damage. When a bacterium is catalase-negative, it indicates that it lacks this protective enzyme, which can be useful for laboratory identification. This characteristic helps microbiologists distinguish between different types of bacteria, often influencing decisions about diagnosis and treatment.