PHYLOGENETIC ANALYSIS OF THE EVOLUTIONARY STABILITY OF THE icaA GENE WITHIN THE GLOBAL STAPHYLOCOCCUS AUREUS POPULATION
DOI:
https://doi.org/10.31861/biosystems2025.02.216Keywords:
Staphylococcus aureus, tonsillitis, icaA, biofilm, phylogenetic analysis, Maximum Likelihood, conservatismAbstract
Staphylococcus aureus is one of the most significant opportunistic pathogens affecting humans and animals. A key factor in its virulence is its ability to form biofilms, which is mediated by the biosynthesis of the polysaccharide intercellular adhesin and encoded by the icaA gene. However, the evolutionary dynamics and degree of conservatism of this gene within the global S. aureus population are not well understood. This study aimed to elucidate evolutionary relationships and assess genetic diversity of the icaA gene among different S. aureus isolates. Twenty-three nucleotide sequences, representative of 14 countries and various ecological niches (clinical, veterinary and environmental), isolated between 2004 and 2025, were analysed. Phylogenetic analysis of the icaA gene (using the maximum likelihood method MEGA 12, GTR+G model) confirmed its conservatism, as all isolates studied formed a dense cluster with short branches, indicating low nucleotide divergence. A main cluster was identified that united isolates from Europe and North America. This cluster has been circulating for over 20 years, indicating the global spread of clones with a stable icaA sequence. The analysis showed that isolates of animal origin from Pakistan did not form a statistically significant subclade, suggesting an absence of local adaptation of the icaA gene in these populations. While some strains from Asia show minor local divergence, the overall tree structure highlights the gene's high stability. The results confirm that the icaA gene is a highly conserved functional gene subject to strong negative selective pressure due to its critical function. This gene's stability may be pivotal to S. aureus' success as a global pathogen.
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