To identify the bacteria causing a sinus infection, a culture is performed by taking a sample from the nasal cavity or sinuses (often via nasal swab or sinus puncture). This sample is then grown in a laboratory on a nutrient-rich medium, allowing any bacteria present to multiply and form visible colonies. These colonies are then tested using various methods, such as Gram staining and biochemical tests, to identify the specific species of bacteria responsible for the infection. This information allows for targeted antibiotic treatment.

Sinus infections, or sinusitis, are most commonly caused by viruses. However, bacteria can also be the culprit, though less frequently than viruses. The most common bacterial causes of acute bacterial sinusitis include:

• Streptococcus pneumoniae: This is a very common bacterium that can cause various respiratory infections.

  

• Haemophilus influenzae: Another common bacterium associated with respiratory infections, including sinusitis.

  

• Moraxella catarrhalis: This bacterium is often found in the upper respiratory tract and can contribute to sinusitis.

  

It's important to note that identifying the specific bacteria causing a sinus infection often requires a culture, and treatment is frequently empirical (based on likely pathogens) rather than targeted at a specific identified bacteria. A doctor will usually only test for bacterial infection if the infection is severe or doesn't respond to initial treatment.