Ann Clin Microbiol 2026;29(3):11. Molecular mechanisms, epidemiology, and clinical implications of macrolide resistance in group A Streptococcus: a narrative review
| emm type | Geographic setting | Reported resistance determinant(s) | Typical phenotype | Representative epidemiological association | Representative reference (first author, year) |
|---|---|---|---|---|---|
| emm4 | Europe, North America | mefA | M phenotype | emm4/ST39 lineage associated with mefA-mediated macrolide resistance | Berbel, 2022 [5]; Silva-Costa, 2015 [6] |
| emm11 | Europe, North America | ermB, often with tet(M) | cMLSB | emm11/ST403 lineage associated with ermB-mediated macrolide resistance | Chochua, 2017 [18]; Silva-Costa, 2015 [6] |
| emm12 | East Asia, Europe, North America | ermB, erm(TR), or mefA depending on lineage and region | cMLSB, iMLSB, or M phenotype | Multiple resistance genotypes reported; ermB-associated resistant emm12 lineages have been prominent in China | Li, 2020 [9]; Cai, 2025 [10]; Chochua, 2017 [18] |
| emm77 | Europe, North America | erm(TR); erm(T) reported in some lineages | Predominantly iMLSB | Resistance genotype varies by clonal background; erm(TR) has been associated with emm77/ST63 | Silva-Costa, 2015 [6]; Chochua, 2017 [18] |
| emm92 | North America | erm(T), often with tet(M) | Predominantly iMLSB | Strong association of emm92/ST82 with erm(T) in US invasive GAS surveillance | Chochua, 2017 [18] |
Associations between emm types and resistance determinants are epidemiological rather than invariant biological characteristics and may differ substantially across geographic regions, study periods, and clonal backgrounds.
Abbreviations: cMLSB, constitutive macrolide-lincosamide-streptogramin B resistance; iMLSB, inducible macrolide-lincosamide-streptogramin B resistance; M phenotype, macrolide efflux phenotype; ST, sequence type.