Is it necessary to take pus on swab in case of abscess in and around tonsil to detect bacteria?or simple saliva around abscess can detect bacteria?

Abscess of tonsil: To get a good bacterial culture from the abscess it is necessary to use a culture swab on the pus itself. Getting a swab of the saliva around the area is not likely to get a good result. Additionally, if the abscess is drained with a needle, then the material from the syringe can be sent on culture swabs.

Much better: To take a swab directly of the site where the infection is. While there might be a very low level of bacteria in the surrounding saliva, for the most part, bacteria are quite sticky and tend to be in much higher concentrations at surfaces at the site of infection. Most of the tests require some threshold level of bacteria for tests to be accurate(otherwise you get false negatives).