TABLE 1.
Antimicrobial susceptibilities of Staphylococcus aureus and Macrococcus canis to erythromycin and pristinamycin IA, as determined by broth microdilution
| Strain/vector | Reference(s) or source | Characteristicsa | MIC (μg/ml)b
|
||
|---|---|---|---|---|---|
| ERY | PIA | iPIAc | |||
| S. aureus | |||||
| RN4220 | 44 | NCTC8325-4 derivative, antibiotic susceptible | 0.25 | 8 | NA |
| RN4220/pTSSCm | 36 | Plasmid with tet(L) | 0.25 | 4 | NA |
| RN4220/pTSSCm-Pcap | 36 | Plasmid with tet(L) | 0.25 | ND | ND |
| RN4220/pTSSCm::mef(D)-msr(F) | This study | Plasmid with mef(D)-msr(F) genes, including upstream sequence (493 bp), tet(L) | 16 | 8 | 8 |
| RN4220/pTSSCm::mef(D) | This study | Plasmid with mef(D), including upstream sequence (493 bp), tet(L) | 1 | 8 | NA |
| RN4220/pTSSCm::msr(F) | This study | Plasmid with msr(F), including 217 bp upstream sequence [3′ end of mef(D) and intergenic region], tet(L) | 0.5 | 4 | NA |
| RN4220/pTSSCm::Δmef(D)-msr(F) | This study | Plasmid with msr(F) fused to upstream sequence of mef(D) (493 bp), tet(L) | 32 | 8 | 8 |
| RN4220/pTSSCm::msr(H) | This study | Plasmid with msr(H), including upstream sequence (698 bp), tet(L) | 2 | 8 | 4 |
| RN4220/pTSSCm::ere-like | This study | Plasmid with ere-like, including upstream sequence containing a transcriptional regulator (tr) (710 bp), tet(L) | 0.25 | ND | ND |
| RN4220/pTSSCm::Δtr-ere-like | This study | Plasmid with ere-like, including tr-deleted upstream sequence (345 bp), tet(L) | 0.25 | ND | ND |
| RN4220/pTSSCm-Pcap::ere-like | This study | Plasmid with ere-like gene controlled by promoter Pcap, tet(L) | 0.25 | ND | ND |
| M. canis | |||||
| KM45013T | 3, 43 | mecB, blaZm | 0.25 | 2 | NA |
| Epi0076A | 9, 12 | mef(D), msr(F), mecB | 4 | 2 | 2 |
| SD0607 | 12 | mef(D), msr(F), ere-like | 16 | 2 | 2 |
| KM0218 | 9, 12 | msr(H), mecB, blaZm, aac(6′)-aph(2ʺ), sat4, aph(3′)-IIIa, erm(B), ant(6)-Ia, tet(S) | >64 | >64 | ND |
Antibiotic resistance genes and their functions are as follows: mef(D), macrolide efflux protein; msr(F) and msr(H), macrolide ABC-F ribosomal protection protein; ere-like, putative erythromycin esterase; tet(L), tetracycline efflux protein; tet(S), ribosome protection tetracycline resistance gene; mecB, penicillin-binding protein 2a (PBP2a) with low affinity for β-lactams; blaZm, β-lactamase; aac(6′)-aph(2ʺ), gentamicin and kanamycin acetyltransferase and phosphotransferase; sat4, streptothricin acetyltransferase; erm(B), macrolide, lincosamide, and streptogramin B 23S rRNA methylase gene; ant(6)-Ia, streptomycin nucleotidyltransferase gene; aph(3′)-III, kanamycin phosphotransferase gene.
ERY, erythromycin; PIA, pristinamycin IA; iPIA, inducible PIA; ND, not determined; NA, not applicable.
iPIA, inducible resistance to pristinamycin IA was measured in the presence of 1 μg/ml erythromycin, except for RN4220/pTSSCm::msr(H), for which the erythromycin concentration was 0.25 μg/ml.