Molecular identification and characterization of mannitol-negative methicillin-resistant Staphylococcus aureus

Area of Science:

• Microbiology
• Infectious Diseases
• Molecular Biology

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) is a significant public health concern.
• Atypical strains of MRSA, such as mannitol-negative variants, present diagnostic challenges.
• Understanding the characteristics of MRSA is crucial for effective treatment and control.

Purpose of the Study:

• To isolate and characterize mannitol-negative MRSA from clinical samples in KwaZulu-Natal, South Africa.
• To identify the genetic makeup, including SCCmec type, of these atypical MRSA isolates.
• To assess the performance of standard laboratory identification methods for mannitol-negative MRSA.

Main Methods:

• Phenotypic testing and polymerase chain reaction (PCR) were used for bacterial identification.
• Detection of S. aureus species-specific genes (nuc, coagulase) and the mecA gene.
• SCCmec typing and API STAPH system for isolate characterization.

Main Results:

• Five mannitol-negative MRSA isolates were successfully identified from clinical samples.
• All isolates were confirmed as S. aureus, mecA positive, and harbored type IV SCCmec.
• The API STAPH system misidentified two isolates as Staphylococcus lugdunensis.

Conclusions:

• Mannitol-negative MRSA strains, particularly those with type IV SCCmec, are present in South Africa.
• Standard biochemical identification methods may misidentify these atypical MRSA strains.
• Laboratories should investigate S. aureus isolates with unusual characteristics to ensure accurate diagnosis.