Characterization of antimicrobial resistance determinants in clinically important Staphylococcus aureus isolates from hospital-acquired infections.

Project Abstract

Staphylococcus aureus remains a major cause of hospital-acquired infections (HAIs) globally, with antimicrobial resistance (AMR) escalating treatment failures and patient morbidity. This study characterizes the genetic determinants and phenotypic resistance profiles of clinically relevant S. aureus isolates collected from diverse hospital wards over a 24-month period, aiming to elucidate the distribution, co-occurrence, and mobility of resistance genes in relation to virulence factors and clonal lineages. A total of 200 non-duplicate isolates were recovered from bloodstream, wound, respiratory, and urinary tract infections. Antimicrobial susceptibility testing was performed using broth microdilution in accordance with CLSI guidelines, covering beta-lactams, aminoglycosides, macrolides, lincosamides, fluoroquinolones, glycopeptides, tetracyclines, and trimethoprim-sulfamethoxazole. Phenotypic resistance profiles were correlated with the presence of resistance determinants identified by targeted PCR assays and whole-genome sequencing (WGS) for a representative subset (n=60). WGS data were analyzed to determine multilocus sequence types (MLST), spa types, SCCmec elements, and the repertoire of AMR genes, including mecA/mecC, blaZ, aminoglycoside-modifying enzymes, macrolide-lincosamide-streptogramin (MLS) resistance genes, tetracycline efflux and ribosomal protection genes, fluoroquinolone resistance determinants (gyrA, grlA), and disinfectant tolerance markers. Phylogenetic analyses integrated with resistome and virulome data illuminated clonal expansion patterns and potential horizontal gene transfer events. The study detected high prevalence of mecA-mediated methicillin resistance (MRSA) alongside a significant presence of blaZ among MSSA isolates. Key resistance gene clusters, such as erm(A)/(C) and mph(C), were associated with macrolide resistance and inducible clindamycin resistance, while tet(K) and tet(M) signified tetracycline resistance versatility. Mobile genetic elements, including SCCmec types II and IV and plasmid-borne determinants, appeared central to disseminating resistance within hospital settings, with particular clonal complexes (CC5, CC8, and ST239-like lineages) showing robust association with multidrug resistance and virulence factor co-occurrence (pulsed-field gel electrophoresis corroboration). Our data reveal a significant correlation between certain SCCmec types and nosocomial infection sites, suggesting niche-specific selection pressures. Phenotypic resistance often exceeded predictions based solely on single-gene presence, highlighting the contribution of gene expression regulation and compensatory mutations. Moreover, virulence profiles demonstrated convergence with resistance traits in dominant hospital-adapted clones, potentially enhancing persistence and transmission. The study identifies critical targets for infection control, including the monitoring of high-risk clones and the implementation of stewardship strategies tailored to prevalent resistance mechanisms. Limitations include potential sampling bias toward tertiary-care centers and the need for longitudinal surveillance to capture temporal dynamics. Overall, the integrative resistome-virulome-phylogenomics approach provides a comprehensive landscape of AMR determinants in hospital-associated S. aureus, informing diagnostic, therapeutic, and preventive interventions to mitigate HAIs and curb antimicrobial resistance spread within clinical settings.

Project Overview

What This Project Is About

---

A simple, accessible look at how certain bacteria called Staphylococcus aureus develop resistance to common medicines, and how scientists study these resistance hints in samples from hospital infections.

---

---

The Problem It Addresses

---

Hospitals see infections that do not respond well to standard antibiotics. This project investigates the genetic clues behind that resistance, helping doctors choose better treatments and guiding policies to prevent spread.

---

---

Objectives of the Project

---

1. Identify common resistance genes in Staphylococcus aureus from hospital cases.
2. Describe how these genes interact with antibiotics in real infections.
3. Compare resistance patterns between different hospital units or wards.
4. Explain the practical consequences for patient care and infection control.

---

---

What You Will Do Step by Step

---

1. Review basic microbiology and antibiotic immunity concepts.
2. Collect or access bacterial samples from hospital infection cases.
3. Test samples to see which antibiotics they resist.
4. Use simple genetic tests to spot resistance genes.
5. Organize and summarize data to look for patterns.
6. Discuss what findings mean for treatment choices and safety.

---

---

Expected Outcome

Clear understanding of which resistance genes are most common, how they affect antibiotic choices, and practical recommendations for managing hospital infections and preventing spread.