Abstract
Background:
Staphylococcus aureus is an opportunistic pathogen responsible for a wide range of infections in humans and animals, including ocular infections in companion animals such as cats and dogs. Molecular identification based on the 16S rRNA gene provides a reliable approach for accurate bacterial detection and phylogenetic analysis.

Aim:
This study aimed to molecularly characterize S. aureus isolates obtained from humans, cats, and dogs using 16S rRNA gene sequencing in order to assess genetic diversity and evaluate the potential for zoonotic transmission.

Methods:
Ocular swab samples were collected from humans (n = 100), cats (n = 50), and dogs (n = 50) between July 2023 and January 2024. Isolates were identified using conventional culture and biochemical methods, followed by polymerase chain reaction amplification of the 16S rRNA gene. Based on antibiotic resistance profiles, 25 representative isolates (10 from cats, 10 from dogs, and 5 from humans) were selected for sequencing and phylogenetic analysis.

Results:
Sequencing analysis confirmed the identity of all selected isolates as S. aureus. Genetic analysis demonstrated both similarities and variations among isolates derived from different hosts, indicating genetic diversity and suggesting possible cross-species transmission between humans and companion animals.

Conclusion:
The findings highlight the genetic diversity of S. aureus isolates from humans, cats, and dogs and support the potential role of companion animals in the zoonotic transmission of this pathogen. Molecular characterization using the 16S rRNA gene is a valuable tool for tracking bacterial evolution and understanding public health risks associated with pathogens shared between humans and animals. Continuous surveillance of antimicrobial resistance and molecular epidemiology is essential, particularly in environments with close human–animal contact.

Key words: Staphylococcus aureus; 16S rRNA; Zoonotic transmission; Genetic diversity; Molecular characterization.