Molecular Profiling of Virulence and Antimicrobial Resistance in Streptococcus pneumoniae Isolated from Respiratory Specimens: A Prospective Tertiary Care Hospital Study

Background: Streptococcus pneumoniae (S. pneumoniae) is a major cause of illness and mortality globally across age groups. WHO has categorized Streptococcus pneumoniae as an agent of top concern due to its high disease burden and growing resistance to commonly used antibiotics. This study holds significant clinical and public health implications and seeks to strengthen antibiotic stewardship efforts by providing data-driven insights into resistance trends to ensure more effective management of pneumococcal infections. Objective: To determine the molecular characteristics and resistance profile of Streptococcus pneumoniae isolated from respiratory samples of LRTI patients. Methods: This observational prospective study was conducted over one year in the Clinical Microbiology Lab at Chettinad Hospital and Research Institute, Tamil Nadu, to analyze the microbiological and molecular characteristics of isolates (Streptococcus pneumonia) from 50 patients having lower respiratory airway infections (LRTIs), including pneumonia. Results: Analysis of the antimicrobial resistance patterns of 50 Streptococcus pneumoniae isolates from patients with LRTIs revealed high resistance to cotrimoxazole (90%), tetracycline (66%), and erythromycin (60%). Every single isolate showed sensitivity to a range of antibiotics, including cefotaxime, vancomycin, azithromycin, linezolid, and cefazolin. Polymerase chain reaction (PCR) interpretation for the lytA and folA genes provided additional insights into pneumococcal pathogenesis and antimicrobial resistance. The lytA gene, which encodes autolysin and is essential for cell wall degradation, was detected in 45/50 (90%) isolates, confirming its virulence. The folA gene, associated with resistance to cotrimoxazole, was also detected in 45/50 (90%) isolates, correlating well with the observed resistance patterns. Conclusion: Among the 50 isolates, 76% originated from sputum, and were obtained predominantly from female patients (60%) and those aged 19-60 years (46%). High resistance rates were noted for cotrimoxazole (90%), tetracycline (66%), and erythromycin (60%). All isolates remained fully susceptible to cefotaxime, vancomycin, linezolid, azithromycin, and cefazolin. The folA gene was detected in all cotrimoxazole-resistant strains, confirming its role in resistance. The identification of lytA as a pneumococcal marker and detection of lytA-negative and optochin-sensitive strains suggests alternative autolysin pathways in pneumococci.