ST8:USA300

Detailed article on ST8:USA300, a strain of MRSA

ST8:USA300 is a strain of methicillin-resistant Staphylococcus aureus (MRSA) that is notable for its virulence and prevalence in community-associated infections. It is a significant public health concern due to its resistance to multiple antibiotics and its ability to cause severe infections.

Background

Staphylococcus aureus is a common bacterium that can be found on the skin and in the nasal passages of healthy individuals. While it is often harmless, it can cause a range of infections, from minor skin infections to life-threatening diseases such as pneumonia, endocarditis, and sepsis. Methicillin-resistant Staphylococcus aureus (MRSA) is a type of S. aureus that has acquired resistance to methicillin and other beta-lactam antibiotics, making it more difficult to treat.

Emergence of ST8:USA300

ST8:USA300 is a specific clone of MRSA that was first identified in the United States in the early 2000s. It is characterized by its sequence type (ST8) and its association with the USA300 pulsed-field gel electrophoresis (PFGE) type. This strain has become the predominant cause of community-associated MRSA (CA-MRSA) infections in the United States.

Genetic Characteristics

ST8:USA300 is distinguished by several genetic markers:

• The presence of the staphylococcal cassette chromosome mec (SCCmec) type IV, which carries the mecA gene responsible for methicillin resistance.
• The presence of the Panton-Valentine leukocidin (PVL) genes, which encode toxins associated with increased virulence and the ability to cause necrotizing pneumonia and skin infections.
• The arginine catabolic mobile element (ACME), which may enhance the bacterium's ability to colonize the skin and mucosal surfaces.

Clinical Significance

ST8:USA300 is associated with a variety of infections, including:

• Skin and soft tissue infections (SSTIs), such as abscesses, cellulitis, and impetigo.
• Invasive infections, such as bacteremia, osteomyelitis, and necrotizing fasciitis.
• Pneumonia, particularly necrotizing pneumonia, which can be severe and rapidly progressive.

Epidemiology

Since its emergence, ST8:USA300 has spread widely across the United States and has been reported in other countries. It is primarily associated with community settings, but it has also been identified in healthcare-associated infections. The strain's ability to spread easily and cause outbreaks has made it a focus of public health efforts.

Prevention and Treatment

Preventing the spread of ST8:USA300 involves standard infection control measures, such as hand hygiene, wound care, and environmental cleaning. Treatment of infections caused by this strain may require the use of non-beta-lactam antibiotics, such as vancomycin, clindamycin, or linezolid, depending on the susceptibility profile of the isolate.

Research and Future Directions

Ongoing research is focused on understanding the genetic basis of ST8:USA300's virulence and resistance, as well as developing new strategies for prevention and treatment. Vaccines and novel antimicrobial agents are areas of active investigation.

Also see

• Methicillin-resistant Staphylococcus aureus
• Staphylococcus aureus
• Panton-Valentine leukocidin
• Antibiotic resistance