Introduction: Staphylococcus aureus (S. aureus) is a Gram-positive, nonmotile, coagulase-positive bacterium, and it is undoubtedly the most clinically significant species in the Staphylococcus genus, which comprises 52 species and 28 subspecies. Approximately 20–40% of the general human population carries S. aureus as part of their nasal microbiota. The emergence of methicillin-resistant Staphylococcus aureus (MRSA) was first identified in England in 1961, shortly following the introduction of methicillin into clinical use. Although methicillin has been withdrawn from the market due to its toxicity and replaced by more stable alternatives such as oxacillin and flucloxacillin, the term MRSA continues to be widely utilized in medical contexts.
MRSA clones primarily develop through horizontal gene transfer of the staphylococcal cassette chromosome mec (SCCmec), a mobile genetic element that encodes the mecA or mecC genes, which confer resistance to methicillin and most β-lactam antibiotics. S. aureus exhibits a distinctive capacity to acquire resistance to various antibiotics, complicating treatment strategies. The global spread of MRSA has profound implications for the epidemiology of infectious diseases. Interestingly, while MRSA is commonly believed to have emerged with the introduction of methicillin, whole-genome sequencing indicates that it likely originated in the mid-1940s, a phenomenon thought to be driven more by the extensive use of penicillin than by methicillin itself.
Methods: To identify MRSA, microbiological specimens are classified into clinical and screening samples. Clinical samples, including septic discharge, deep tissues, sputum, and blood, are collected from symptomatic individuals for diagnosing active infections. Conversely, screening samples such as nasal, perineal, and throat swabs aim to detect asymptomatic carriers. Various phenotypic methods, which dominate clinical settings, as well as innovative non-phenotypic techniques, are employed for MRSA detection. Glycopeptides like vancomycin and teicoplanin serve as primary treatments for MRSA infections, with combination therapies investigated to enhance bacterial clearance, although evidence for their superiority remains inconclusive. The duration of treatment for MRSA bacteremia is generally more prolonged than for MSSA, necessitating a minimum 14-day regimen to reduce complication risks. Emerging antibiotic agents such as ceftaroline and ceftobiprole show promise against MRSA, yet concerns about resistance underscore the urgent need for continued research in this evolving field.
Results: The prevalence of MRSA varies geographically, with the highest rates observed in parts of America and Asia, while lower incidences are noted in Scandinavia. MRSA dissemination occurs through existing resistant clones and the acquisition of SCCmec by methicillin-sensitive S. aureus (MSSA) strains. Colonization by S. aureus typically precedes the onset of infection, predominantly occurring in the nasal passages, although colonization can also take place in other sites. Skin and soft tissue infections (SSTIs) often result from bacterial transfer from the nares to skin lesions, facilitated by specific surface proteins that enhance the bacteria’s adherence and biofilm formation on surfaces.
Conclusion: In conclusion, Staphylococcus aureus, particularly its methicillin-resistant strain (MRSA), poses a significant threat to public health due to its ability to acquire antibiotic resistance and its prevalence within the human population. Despite the withdrawal of methicillin, MRSA's emergence highlights the consequences of extensive antibiotic use, including the ability of the bacterium to spread through horizontal gene transfer. The identification and management of MRSA infections require robust diagnostic methods and appropriate treatment strategies, often necessitating prolonged therapy. To combat this growing challenge, innovative approaches such as the development of novel antibiotics, the use of bacteriophages, and enhanced emphasis on infection control measures in healthcare settings should be pursued. Additionally, ongoing research into vaccine development and public education on antibiotic stewardship is critical to mitigate the impact of MRSA.
Keywords: Staphylococcus aureus (S. aureus), Methicillin-resistant Staphylococcus aureus (MRSA), public health