Many different ones. Acute sinusitis is usually caused by some bacteria and chronic sinusitis is often cause by different ones. Oftentimes the infection may have more than one bacteria. The exact bacteria isn't generally important in acute sinusitis, as they usually respond well to typical antibiotics. If you have chronic sinusitis your ENT may recommend a culture of your nose to further investigate things.
Top 3... The top 3 bacteria causing acute sinusits in a typical patient are: 1. Streptococcus pneumoniae 2. Haemophilus influenzae 3. Moraxella catarrhalis most infections are proceeded by a viral sinusitis and then it will progress to a bacterial infection.