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. 2025 Dec 27.
doi: 10.1007/s11845-025-04234-6. Online ahead of print.

Molecular phylogenetic and biochemical characterization of Staphylococcus aureus isolates from non-sterile pharmaceutical cough formulations: An insight into genetic diversity

Kajal Sharma  1 , Sonika Bakshi  1 , Paruv Sachdeva  1 , Meesala Krishna Murthy  2
Affiliations

Molecular phylogenetic and biochemical characterization of Staphylococcus aureus isolates from non-sterile pharmaceutical cough formulations: An insight into genetic diversity

Kajal Sharma et al. Ir J Med Sci. .

Abstract

Background: Contamination of cough syrups not produced under sterile conditions is dangerous for users and can affect product quality.

Methods: The bacterial quality was investigated in 15 cough syrup samples collected from Punjab, India (validity: January-June 2024). This was confirmed when contamination was measured via membrane filtration (0.45 μm pores) and microbes were grown on Tryptone Soya Agar, mannitol salt agar, Xylose Lysine Deoxycholate Agar and Eosin Methylene Blue Agar. The number of isolates (CFU/mL) was determined, and the isolates were identified using Gram staining, biochemical tests, and 16S-rRNA gene sequencing.

Results: The presence of genetic variation among organisms was also evaluated. Only one out of 15 samples (6.66%) had levels higher than allowed, three others (20%) were near the limit, and the rest (73.33%) were below the United States Pharmacopeia (USP) limit ( 10³ CFU/mL) for bacterial contamination. Staphylococci sp. were present in syrups C, D, L, and O according to biochemical testing. The results for syrup C showed that Staphylococcus aureus (GenBank: PV137763) was above the level required by the USP. Genetic diversity analysis revealed six main haplotypes, with a high haplotype diversity (Hd= 0.8667) and nucleotide diversity (Pi = 0.09097), suggesting that the population is either expanding or undergoing purifying selection.

Conclusion: The majority of syrups were of good quality; however, there were contaminated samples, which raised doubts about how they were produced. It is recommended that good manufacturing practices be strictly enforced. Larger and ongoing quality control studies should be conducted to evaluate product safety.

Keywords: Staphylococcus aureus; 16S-rRNA sequencing; Bacterial load; Genetic diversity; USP standards.

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Conflict of interest statement

Declarations. Ethical approval: Not applicable. Consent to participate: Not applicable. Consent to publish: Not applicable. Conflicts of interest: Authors declare no conflict of interest.

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