Table 1.

In vitro activity of antimicrobial agents againstS. pneumoniae and S. pyogenes isolates

OrganismAntimicrobial agentaMIC (μg/ml)No. (%) of isolates that were:
50%90%SusceptibleIntermediateResistant
S. pneumoniaePenicillin0.1252839 (49.8)479 (28.4)366 (21.7)
Amoxicillin0.0621,519 (90.2)79 (4.7)86 (5.1)
Amoxiclavb0.0621,522 (90.4)75 (4.4)87 (5.1)
Cefaclor≤1≥64893 (53.0)90 (5.3)701 (41.6)
Cefuroxime≤0.2581,008 (59.8)147 (8.7)529 (31.4)
Cefiximec0.5≥4
Cefotaxime≤0.2511,287 (76.4)282 (16.7)115 (6.8)
Erythromycin≤0.12≥641,096 (65.1)0 (0)588 (34.9)
Clarithromycin≤0.25≥641,097 (65.1)3 (0.2)584 (34.7)
Azithromycin≤0.12≥641,062 (63.1)37 (2.2)585 (34.7)
Ciprofloxacinc, d12120 (7.1)
S. pyogenesPenicilline≤0.015≤0.0152,039 (100)0 (0)0 (0)
Erythromycin≤0.1281,621 (79.5)2 (0.1)416 (20.4)
Clarithromycin≤0.2581,622 (79.5)6 (0.3)411 (20.2)
Azithromycin≤0.1281,520 (74.5)103 (5.0)416 (20.4)
Ciprofloxacinc, d1170 (3.4)
  • a Breakpoints used for S. pneumoniae were ≤0.06 μg/ml (susceptible), 0.12 to 1 μg/ml (intermediate), and ≥2 μg/ml (resistant) for penicillin; ≤2 μg/ml (susceptible), 4 μg/ml (intermediate), and ≥8 μg/ml (resistant) for amoxicillin and amoxicillin-clavulanate; ≤1 μg/ml (susceptible), 2 μg/ml (intermediate), and ≥4 μg/ml (resistant) for cefaclor and cefuroxime axetil; ≤0.5 μg/ml (susceptible), 1 μg/ml (intermediate), and ≥2 μg/ml (resistant) for cefotaxime and azithromycin; and ≤0.25 μg/ml (susceptible), 0.5 μg/ml (intermediate), and ≥1 μg/ml (resistant) for erythromycin and clarithromycin. Breakpoints used for S. pyogenes were ≤0.12 μg/ml (susceptible), 0.25 to 2 μg/ml (intermediate), and ≥4 μg/ml (resistant) for penicillin; ≤0.5 μg/ml (susceptible), 1 μg/ml (intermediate), and ≥2 μg/ml (resistant) for azithromycin; and ≤0.25 μg/ml (susceptible), 0.5 μg/ml (intermediate), and ≥1 μg/ml (resistant) for erythromycin and clarithromycin.

  • b Amoxiclav, amoxicillin-clavulanate (2:1). The concentrations listed are for amoxicillin.

  • c No NCCLS breakpoints have been established.

  • d Arbitrary ciprofloxacin breakpoint for resistance, ≥4 μg/ml.

  • e In accordance with NCCLS, a streptococcal isolate that is susceptible to penicillin is considered susceptible to the remaining β-lactams.