Prevalence of infections due to Methicillin Resistant Staphylococcus aureus (MRSA) and the phenotypic and genotypic characterization on the clinical MRSA isolates

• Author Details:   
• Rajalakshmi Kesavan
• Asha A
• Sumetha Suga D
• Ananthi B

Introduction: A superbug is a type of bacteria that has evolved resistance to antibiotics that are used to treat common and severe infections. One such bacteria is Methicillin Resistant Staphylococcus aureus (MRSA). Since the number of nosocomial infections caused by MRSA which are resistant to all β-lactam antibiotics is on the rise globally, detecting them is crucial for therapeutic reasons. Hence clinical microbiologists should find a way to identify Staphylococcus aureus isolates as MRSA and report their findings correctly and quickly.

Aim and Objective: 1. To detect the prevalence of MRSA strains from the various clinical specimens; 2. To study the antibiotic susceptibility pattern of MRSA isolates by disc diffusion method, 3.To detect MRSA by Phenotypic and Genotypic methods.

Materials and Methods: A cross-sectional study was carried at ACS Medical College and Hospital in Chennai for a period of one year from September 2022 to October 2023. A total of 100 non-duplicate MRSA isolates from various clinical samples were collected and specific phenotypic tests for screening and confirmation of MRSA were done as per CLSI guidelines (32nd and 33rd edition). Specific genotypic tests for detection of mecA gene will be done by Real Time Polymerase Chain Reaction (RT- PCR).

Result: Male predominance was higher in this study of about 55% with majority of 39% were between 41-60 years. Outpatient and inpatient scenarios were used to classify MRSA isolates. The inpatient group had the highest number of MRSA isolates (94%). Among the 94 inpatients, 28(29.8%) remained longer than 2 weeks, whereas 66(70.2%) stayed for less than 2 weeks. Nearly majority of the MRSA isolates (98%) developed bluish-green coloured colonies on CHROMagar. mecA gene was detected in all 50 samples by RT-PCR method. Among 100 MRSA isolates, highest resistance was observed in Azithromycin (79%) followed by Ciprofloxacin (78%) and Erythromycin (64%). All 100 isolates were susceptible for Vancomycin and Linezolid. Among 33 Clindamycin resistant MRSA isolates, 60.6% isolates showed inducible clindamycin resistance and 39.4% showed constitutive resistance.

Conclusion: The high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infections in India highlights the urgent need to implement surveillance and prevention measures in healthcare facilities and the general public to curb the infection's spread. Thanks to its high sensitivity, specificity, ease of interpretation, and rapid results, CHROMagar is an effective diagnostic tool for Methicillin resistance. A number of previous studies have demonstrated that the gold standard method for finding mecA gene is Real-Time Polymerase Chain Reaction (PCR).