TABLE 1.

Macrolide resistance phenotypes and correlations with erythromycin resistance genes and serotypes in 120 clinical isolates of erythromycin-resistant S. pneumoniae

Phenotype of macrolide resistanceNo. (%) of strainsAntibioticaMIC (μg/ml)bNo. of strains with gene:Serotype (no. of strains)
Range50%90%erm(AM)mef(A)mef(E)
cMLS20 (16.7)Erythromycin64->128128>12820123F (5), 19F (4), 6B (3), 14 (3), 3 (2), 9A (1), 15A (1), 19A (1)
Clindamycin128->128>128>128
Clindamycin (ind.)>128>128>128
Rokitamycin4->12832>128
Rokitamycin (ind.)>128>128>128
iMLS2 (1.7)Erythromycin64->12827F (1), 23F (1)
Clindamycin0.06-0.12
Clindamycin (ind.)>128
Rokitamycin≤0.03-0.25
Rokitamycin (ind.)>128
iMcLS59 (49.2)Erythromycin4->128128>128591419A (11), 23F (10), 19F (9), 6B (6), 3 (5), 6A (3), 10F (3), 14 (3), 10A (2), 23A (2), 9V (1), 15A (1), 20 (1), 33F (1), 36 (1)
Clindamycin2->12864>128
Clindamycin (ind.)32->128>128>128
Rokitamycin≤0.03-10.251
Rokitamycin (ind.)4->128>128>128
M39 (32.5)Erythromycin2-16816231614 (14), 23F (2), 19A (2), 3 (2), 6B (1), 15B (1), 33A (1)c
Clindamycin≤0.03-0.12≤0.030.12
Clindamycin (ind.)≤0.03-0.250.060.1223A (3), 23F (3), 1 (2), 6B (1), 9V (1), 10F (1), 11A (1), 12F (1) 18F (1), 19A (1), 35 (1)d
Rokitamycin≤0.03-0.25≤0.030.25
Rokitamycin (ind.)≤0.03-0.25≤0.030.25
  • a ind., after induction by pregrowth in 0.05 μg of erythromycin per ml.

  • b 50% and 90%, MICs at which 50 and 90% of isolates, respectively, are inhibited.

  • c Isolates carrying the mef(A) gene.

  • d Isolates carrying the mef(E) gene.