Hamadan University of Medical Sciences Avicenna Journal of Clinical Microbiology and Infection 2383-0298 11 3 2024 09 30 In Vitro Investigation of the Effects of Certain Antibiotics and Plant Oils on the Clinical Isolates of Streptococcus pneumoniae 125 129 10.34172/ajcmi.3506 EN Mazen Safi https://orcid.org/0000-0002-2541-0335 Marwa Khawajkiah Nour Al-Sahar Ayman Al-Mariri Journal Article 10.34172/ajcmi.3506 2024 09 01 2024 09 22 Background: With the serial trend toward antibiotic resistance in Streptococcus pneumoniae, novel drug development is needed to deal with pathogenic microorganisms that have developed widespread microbial resistance to antibiotics. Methods: Eighty-seven clinical samples were collected from six hospitals in Damascus. A polymerase chain reaction (PCR) was performed to identify the bacterial genus and type. Minimum inhibitory concentrations on Luria-Bertani agar were conducted using several antibiotics and essential oils (EOs). Results: Twenty-five isolates of S. pneumoniae were found, and amoxicillin and cephalosporins were the most effective antibiotics against 90% of S. pneumoniae bacteria. On the other hand, Thymus syriacus Boiss., Origanum syriacum L., Rosmarinus officinalis L., Cinnamomum zeylanicum L., and Juniperus foetidissima Willd were the most effective EOs. Conclusion: Only T. syriacus Boiss., O. syriacum L., R. officinalis L., C. zeylanicum L., and J. foetidissima Willd oils had good inhibitory effects against S. pneumoniae.