Final answer:
The most appropriate laboratory test for a patient with an acute bacterial infection unresponsive to antibiotics is a Culture and sensitivity test. This will identify the bacteria and their antibiotic susceptibility, guiding effective treatment. Therefore, the correct option is D.
Step-by-step explanation:
In a patient with an acute bacterial infection that does not respond to routine antibiotic therapy, the most appropriate laboratory test to perform would be Culture and sensitivity. This test allows for the identification of the specific bacteria causing the infection as well as determination of the antibiotics to which the bacteria are sensitive. This is critical for guiding effective treatment.
To determine if the infection is caused by staphylococcal or streptococcal bacteria, a lab technician could perform a Gram stain to differentiate between gram-positive and gram-negative bacteria. Based on the Gram stain results, other tests like agglutination assays could be used to detect the presence of specific bacteria. Additionally, a direct fluorescent antibody test might be performed to look for bacteria in a patient sample using a fluorescently-labeled monoclonal antibody.
For determining the best course of antibiotic treatment, apart from culture and sensitivity, tests such as antibiotic susceptibility tests are crucial. They inform the healthcare provider about which antibiotics are effective against the specific strain of bacteria identified from the patient's sample.