The multifaceted resources and microevolution of the successful human and animal pathogen methicillin-resistant Staphylococcus aureus

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important bacterial pathogens based on its incidence and the severity of its associated infections. In addition, severe MRSA infections can occur in hospitalised patients or healthy individuals from the community. Studies have shown the infiltration of MRSA isolates of community origin into hospitals and variants of hospital-associated MRSA have caused infections in the community. These rapid epidemiological changes represent a challenge for the molecular characterisation of such bacteria as a hospital or community-acquired pathogen. To efficiently control the spread of MRSA, it is important to promptly detect the mecA gene, which is the determinant of methicillin resistance, using a polymerase chain reaction-based test or other rapidly and accurate methods that detect the mecA product penicillin-binding protein (PBP)2a or PBP2’. The recent emergence of MRSA isolates that harbour a mecA allotype, i.e., the mecC gene, infecting animals and humans has raised an additional and significant issue regarding MRSA laboratory detection. Antimicrobial drugs for MRSA therapy are becoming depleted and vancomycin is still the main choice in many cases. In this review, we present an overview of MRSA infections in community and healthcare settings with focus on recent changes in the global epidemiology, with special reference to the MRSA picture in Brazil.

Molecular and phenotypic characteristics of methicillin-resistant Staphylococcus aureus isolated from hospitalized patients

“…The gene mecA is inserted into a mobile genetic element (MGE) known as staphylococcal cassette chromosome mec (SCCmec), and currently, eleven types (SCCmec I to XI) have been described in MRSA strains isolated from various sources [7][8][9][10].…”

What is behind the epidemiological difference between community-acquired and health-care associated methicillin-resistant Staphylococcus aureus?

“…MRSA isolates were first reported among hospitalized patients at the beginning of the 1960s, and remain major agents of hospital infections worldwide. 1 Typical lineages (clones) of health care-associated MRSA (HA-MRSA) are ST5 (CC5), ST239 (CC8), ST22 (CC22), and ST36 (CC30). However, these rarely cause infections in healthy individuals who are not hospitalized or attended a healthcare service in the 6-12 months before infection.…”

“…Nevertheless, the factors involved in the local expansion of a specific CA-MRSA lineage and the mechanisms behind the bacterial diversification in HA-or CA-MRSA remain unclear. 1 In the 2000s, CA-MRSA emerged in hospital settings to compete with HA-MRSA clones, representing an important epidemiological change. The PVL-positive, CA-MRSA USA300 is now challenging the previously dominant HA-MRSA clone New York/Japan (ST5) in USA hospitals.…”

“…5 In Rio de Janeiro, Brazil, the CA-MRSA ST30 is frequently detected causing typical HA-infections including septicemia. 1 A legitimate concern of the scientific community is related to the possibility that once in hospitals the CA-MRSA could exchange DNA with typical HA-MRSA clones and thus acquire multiple-resistant genes. There is also the possibility that the intense CA-MRSA dissemination in health care units might facilitate the acquisition of additional adaptive mutations to increase bacterial fitness and survival despite the costs of antibiotic resistance.…”

“…Here, a PVL-negative clone related to a classical CA-MRSA lineage is largely confined to hospitals. 1 The hospital-restricted and multiresistant ST1-SCCmecIV, PVL-negative, related to the USA400 CA-MRSA-a PVL-positive strain previously detected causing CA infections in USA and Canada-emerged in Brazilian hospitals. 6 This is a good example of this epidemiological change that can even further challenge the distinction between CA-MRSA and HA-MRSA.…”