Activated sludge comprises numerous advantageous microorganisms that have the ability to stabilize organic waste. The purpose of this study is to isolate and identify microbial strains capable of oxidizing ammonia in poultry slaughterhouse wastewater to diminish nitrogen levels in wastewater. Diluted activated sludge samples were inoculated onto nutrient agar plates with varying concentrations of (NH4)2SO4 and NH4Cl to isolate tolerant bacterial strains. Eight isolates, namely SO1K, SO3K, SO1OR, SO4PB, SO3P, SO4PM, CL3P, and CL5P, cultivated in a medium containing 50 g/L (NH4)2SO4 or NH4Cl were recovered from the activated sludge sample. Morphological and biochemical methods were employed to identify all of the bacterial isolates. The 16S rRNA genetic sequence was employed to identify four isolates using the molecular approach. Brevibacterium sp. was genetically related to strain SO1K, as evidenced by a 99.86% similarity in the 16S rRNA gene sequence. Strain SO3K exhibited 99.43% similarity to Rothia koreensis. Meanwhile, strain SO1OR and strain SO4PB demonstrated 100% sequence similarity to Staphylococcus aureus and Staphylococcus epidermidis, respectively, indicating a very close phylogenetic relationship. The examination of bacterial growth and ammonium reduction measurements demonstrated that strains SO1K, SO3K, SO1OR, and SO4PB were capable of growing in medium with elevated nitrogen concentrations and efficiently diminished the nitrogen levels in the medium. Specifically, SO1K reduced ammonium by 92.15%, SO3K by 95.77%, SO1OR by 98.63%, and SO4PB by 99.78%, indicating their potential as ammonia-oxidizing agents.