Genetic diversity among methicillin-resistant Staphylococcus epidermidis (MRSE)

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• Staphylococcus epidermidis is a common hospital pathogen.
• Methicillin resistance in S. epidermidis (MRSE) is a growing concern.
• Understanding the genetic basis of MRSE is crucial for infection control.

Purpose of the Study:

• To investigate the genetic diversity of methicillin-resistant S. epidermidis (MRSE) and methicillin-susceptible S. epidermidis (MSSE) hospital isolates.
• To characterize the variation in mobile genetic elements, particularly SCCmec, within these isolates.
• To explore the relationship between genetic diversity and the presence of antibiotic resistance genes.

Main Methods:

• Pulsed-field gel electrophoresis (PFGE) was used for strain typing.
• DNA hybridization with probes for mecA, orfX, gyrA, murE, and aroE genes was performed.
• SCCmec typing was conducted to identify different cassette structures.

Main Results:

• Extensive variation was observed in DNA fragments associated with mecA, orfX, and gyrA genes across MRSE and MSSE isolates.
• Housekeeping genes murE and aroE showed limited size variation, indicating localized genetic instability.
• Ten different SCCmec structures were identified, with a significant number of non-typeable strains. SCCmec type IV-like structures were most common (36%).
• Closely related strains sometimes carried different SCCmec types, while unrelated strains could share similar SCCmec structures.

Conclusions:

• The acquisition and loss of mobile genetic elements, including SCCmec, occur frequently near the orfX gene in S. epidermidis.
• This dynamic genetic landscape contributes to the evolution and spread of methicillin resistance in hospital-acquired S. epidermidis infections.
• Further research into the mechanisms of mobile genetic element exchange is warranted.