Prevalence, toxin virulence genes and investigating the effect of mutations in the tetracycline gene (tetK) on the response of methicillin-resistant Staphylococcus aureus to antibiotics: a study in sickle cell disease patients in Riyadh, Saudi Arabia

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen associated with antimicrobial resistance, particularly in bloodstream infections affecting individuals with underlying conditions such as sickle cell disease (SCD). Resistance to tetracycline and erythromycin in MRSA is often mediated by efflux pump genes, including tetK, tetM, ermA, and ermC. These genes play a crucial role in reducing the efficacy of commonly used antibiotics, posing significant challenges in clinical management. Understanding the genetic variations within these resistance genes and their association with phenotypic resistance patterns is essential for guiding effective treatment strategies and improving patient outcomes. However, earlier research has not thoroughly examined how changes in the genes tetK, tetM, ermA, and ermC relate to the antibiotic resistance seen in MRSA strains taken from SCD patients. This gap indicates that there must be a focused investigation to bridge the current knowledge deficit and support the development of more targeted therapeutic approaches. This study aimed to investigate the prevalence and genetic basis of antibiotic resistance in MRSA bloodstream isolates from sickle cell disease patients in Riyadh, Saudi Arabia. It looked at the resistance genes, like tetK, ermA, and ermC, and studied how changes in their sequences affected them using evolutionary and structural analysis over seven years. MRSA isolates (n = 34) were obtained from 3,979 SCD patients (2017-2024). Representative strains were analyzed for their antibiotic susceptibility using the VITEK 2 system and PCR-based identification of resistance genes (e.g., tetK, tetM, ermA, and ermC). Among SCD patients, 0.9% exhibited MRSA bloodstream infections, predominantly affecting individuals over 20 years of age. During our study, we made an intriguing discovery that the toxin genes (hlg, hla, Pvl, and sea) were predominant in the MRSA isolates. Sequencing of tetK, ermA, ermC, and 16S rRNA genes was performed, and variations were analyzed using bioinformatics tools (BLAST, MEGA X, CARD, BLASTX). Phylogenetic analysis was conducted, and the results were correlated with phenotypic resistance profiles. All isolates were resistant to β-lactam antibiotics but sensitive to vancomycin and tobramycin. The analysis of the genetic sequence revealed important changes in the tetK gene, with strain RHD-KSA30 exhibiting several different amino acids. Phylogenetic analysis grouped Riyadh strains into distinct clusters. Variations in tetK correlated with differential susceptibility to antibiotics like erythromycin, clindamycin, and ciprofloxacin. The genetic diversity of the tetK gene in MRSA strains and its function in mediating antibiotic resistance are highlighted in this study. Although vancomycin and tobramycin are still effective treatments, the resistance to other antibiotics shows the need for continuous monitoring and the development of tailored treatment plans, especially for high-risk groups like patients with sickle cell disease (SCD).