Abstract
Tonsillitis is an inflammatory condition of the palatine tonsils, most commonly caused by Streptococcus pyogenes. This bacterium produces Streptolysin O (SLO), a cytolytic toxin that stimulates inflammatory cytokines and may contribute to chronic infection. Recurrent tonsillitis often results from incomplete bacterial eradication, emphasizing the importance of identifying causative agents and immune responses. The study aimed to identify the main bacterial pathogens associated with acute and chronic tonsillitis and to measure serum Streptolysin O levels among infected patients. This study was conducted at the ENT Unit of Al-Yarmook Teaching Hospital, Baghdad, from January 2024 to January 2025. A total of 120 samples were collected, including 90 throat swabs from patients with chronic tonsillitis and 30 blood samples from healthy controls. Bacterial identification was performed using biochemical tests and confirmed by the VITEK system, while serum SLO levels were determined by ELISA. Out of 90 patients, 57 (63.3%) were females, and 33 (36.7%) were males, with a ratio female-to-male of 1:1.73. All patient swabs showed bacterial growth, while controls were negative. The isolates included S. pyogenes (74%), S. pneumoniae (14.4%), S. aureus (7.8%), and S. viridans (4.4%). Serum SLO levels were significantly higher in chronic cases (mean = 90.14 pg/mL). Streptococcus pyogenes was the predominant pathogen linked to chronic tonsillitis, suggesting its central role in disease recurrence. Elevated SLO levels may serve as a biomarker of chronicity.