Final answer:
Antibiotics are able to target and kill both gram-positive and gram-negative bacteria, which are differentiated through the Gram stain test, especially in cases like bacterial meningitis where early treatment is crucial.
Step-by-step explanation:
The types of microorganisms that would be killed by antibiotic treatment are primarily bacteria. Antibiotics are designed to target bacterial infections, either by killing the bacteria or inhibiting their growth. In the context of a lumbar puncture to test for bacterial meningitis, antibiotics can be effective against both gram-positive and gram-negative bacteria, which are distinguished by the Gram stain test mentioned in the reference material. While the Gram stain did not show any bacteria in Cora's cerebrospinal fluid (CSF), the doctor prescribed antibiotics as a precautionary measure, which can be important in cases where bacterial growth has not yet reached sufficient levels to be detected by the Gram stain but may still be present and potentially harmful.