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Saudi Journal of Pathology and Microbiology (SJPM)
Volume-11 | Issue-06 | 164-173
Original Research Article
Conventional Phenotypic Identification and Serotype Characterization of Streptococcus Pneumoniae in Respiratory Specimens from Baghdad, Iraq
Suadad Taha Obaid, Elaf Basim Noori, Ahlam Gareeb Nhaer
Published : Aug. 10, 2026
DOI : https://doi.org/10.36348/sjpm.2026.v11i06.002
Abstract
Background: Streptococcus pneumoniae remains an important bacterial cause of lower respiratory tract infection. Although molecular methods are becoming more available, many hospital microbiology laboratories in Iraq still depend on conventional phenotypic identification. So, this workflow is still not old practice only; it is part of the daily diagnostic work. Objective: To assess the practical diagnostic value of conventional phenotypic methods for identifying S. pneumoniae from respiratory specimens in a routine clinical microbiology laboratory in Baghdad, Iraq. Methods: This prospective, single-center, laboratory-based observational study was performed at the Microbiology Laboratories of Baghdad Medical City from February to May 2026. Seventy-four adult patients with suspected lower respiratory tract infection were enrolled. Respiratory specimens were assessed by direct Gram stain, cultured on 5% sheep blood agar under CO₂-enriched incubation, and screened for alpha-hemolytic colonies. Presumptive isolates were further examined by Gram stain from culture, optochin susceptibility, bile solubility, capsule staining, biochemical identification, and slide agglutination serotyping. Results: Of 74 respiratory specimens, 52 (70.3%) showed neutrophil-predominant inflammatory smears, and 34 (45.9%) showed Gram-positive diplococci on direct microscopy. Bacterial growth was obtained from 58 specimens (78.4%). Thirty-six isolates showed presumptive alpha-hemolytic streptococcal morphology, and 30 were finally identified as S. pneumoniae. The pneumococcal identification rate was 40.5% among all specimens and 83.3% among presumptive alpha-hemolytic isolates. Optochin susceptibility and bile solubility provided the clearest separation between confirmed pneumococci and non-confirmed alpha-hemolytic isolates (p < 0.001 for both), with perfect internal agreement (kappa = 1.00). Serotype 6 was the most frequent serotype, detected in 11 isolates (36.7%), followed by serotype 3 in 4 isolates (13.3%). Conclusion: Conventional phenotypic methods can still provide useful identification of S. pneumoniae in routine Iraqi microbiology laboratories when applied as a combined systematic workflow, not as isolated single tests. Still, because no molecular reference method was used, the findings should be interpreted as pragmatic diagnostic utility rather than full analytical diagnostic accuracy.
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