Clonal diversity and trend of methicillin-resistant/susceptible Staphylococcus aureus (MRSA/MSSA) from a tertiary care hospital in Myanmar: Increase in ST6-IVa/t304 and identification of notable clones ST22-PT, ST2885-ETA, and ST2990-ETE.

OBJECTIVES

Staphylococcus aureus is one of the leading causes of nosocomial infections. This study aimed to clarify the recent trend of molecular epidemiological features of methicillin-resistant and susceptible S. aureus (MRSA/MSSA) isolates from a tertiary care hospital in Myanmar.

METHODS

S. aureus clinical isolates from various specimens were genetically classified by the schemes of MLST and other genotypings. Antimicrobial resistance determinants and virulence factors were detected by uniplex/multiplex PCR, along with antimicrobial susceptibility testing by broth microdilution method.

RESULTS

A total of 319 S. aureus (65 MRSA and 254 MSSA) and 7 S. argenteus isolates were collected during a 19 month-period (Sep. 2023 to Mar. 2025), with an MRSA rate of 20.4%. Panton-Valentine leukocidin (PVL) genes were detected in 30.4% of all the isolates, with almost similar rates in MRSA and MSSA. Among MRSA, ST6 (CC5) with SCCmec-IV (ST6-IV) was the most dominant (31%), followed by ST772 (CC1)-V, ST2885 (CC1)-IV, ST22 (CC22)-IV, and ST672 (CC361)-V. PVL-positive rate was highest in ST22 (75%) and ST121 (84%) among MRSA and MSSA, respectively. PVL-positive ST22 MRSA also harbored TSST-1 gene (ST22-PT clone). Characteristic virulence factors were detected in other MRSA clones; enterotoxin A (SEA) in ST6, exfoliative toxin A (ETA) in ST2885, and exfoliative toxin E (ETE) in ST2990. PVL-positive ST22 and ST772 MRSA showed multiple antimicrobial resistance harboring some resistance genes. MSSA isolates were differentiated into 33 STs, among which ST2990 (CC1) was the most common (24%), followed by ST121, ST1156 (CC12), ST6 (CC5) and ST1930 (CC96). All the S. argenteus were mecA-negative and belonged to ST2250.

CONCLUSIONS

The present study revealed the recent clonal trend and change of MRSA/MSSA isolates in Myanmar, identifying some notable clones with characteristic virulence factors (ST6-SEA, ST22-PT, ST2885-ETA, and ST2990-ETE).