A Decade of Pediatric CA-MRSA Surveillance in Northern Taiwan: Retrospective Resistance Analysis and Recent Genotypic Characterization

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of pediatric infections and has shown evolving molecular characteristics over time. This study aimed to investigate the phenotypic and genotypic features of MRSA isolates collected from pediatric patients at a tertiary medical center in northern Taiwan between 2011 and 2020. A total of 182 MRSA strains were analyzed for SCCmec types, PVL gene presence, antimicrobial susceptibility, multilocus sequence typing (MLST), and clonal relatedness using pulsed-field gel electrophoresis (PFGE). ST59/SCCmec Vt was the most prevalent genotype, followed by ST59/SCCmec IV and ST8/SCCmec IV. Most ST59/SCCmec Vt and ST8/SCCmec IV isolates clustered genetically. Clindamycin and erythromycin resistance remained high, whereas co-trimoxazole susceptibility ranged from 76% to 100%. These findings confirm ST59 as the dominant clone and highlight the emergence of ST8 and ST45 in community-associated MRSA (CA-MRSA) infections. Oral co-trimoxazole remains the most effective empirical option, while clindamycin and erythromycin should be avoided. Continuous molecular surveillance is warranted to monitor trends and guide treatment strategies in pediatric MRSA infections.

Keywords: MRSA; SCCmec; children; clindamycin resistance; co-trimoxazole; genotyping.

Figure 1

Bar charts represent the number of resistant CA-MRSA isolates to clindamycin (blue), erythromycin (orange), and TMP/SMX (gray) during two study periods. Line graphs depict the corresponding susceptibility percentages of each antibiotic: clindamycin (yellow), erythromycin (purple), and TMP/SMX (green). TMP/SMX showed the highest susceptibility rates in both periods.

Figure 2

SCCmec subtypes and PVL gene positivity among 50 CA-MRSA isolates. Bar charts display the number and percentage of CA-MRSA isolates carrying SCCmec type IV or Vt, along with the number of PVL-positive isolates. The line graph shows the PVL gene positivity rate in each group. SCCmec Vt demonstrated the highest PVL positivity rate, suggesting a shift in molecular epidemiology.

Figure 3

Annual resistance and susceptibility trends of CA-MRSA isolates to clindamycin, erythromycin, and TMP/SMX from 2018 to 2020. Bar charts indicate the number of CA-MRSA isolates resistant to clindamycin (blue), erythromycin (orange), and TMP/SMX (gray). Line graphs show the susceptibility percentages for the same antibiotics: clindamycin (yellow), erythromycin (purple), and TMP/SMX (green). TMP/SMX demonstrated the highest and most stable susceptibility, while clindamycin and erythromycin showed lower and more variable trends.

Figure 4

PFGE-based dendrogram showing the clonal relationships among 50 CA-MRSA isolates. Clustering patterns are based on >80% similarity. Most ST59/SCCmec Vt and ST8/SCCmec IV isolates grouped into distinct clonal clusters, suggesting local transmission and clonal expansion of specific MRSA lineages.