TABLE 1.
Antimicrobial susceptibilities of E. corrodens, P. intermedia, and P. nigrescens
| Species (no. of isolates) | Medium used in primary culture | Amoxicillin MIC (μg/ml)a
|
Susceptibility ratesbcd | Tetracycline MIC (μg/ml)a
|
Susceptibility ratesbcd | ||||
|---|---|---|---|---|---|---|---|---|---|
| Range | 50% | 90% | Range | 50% | 90% | ||||
| E. corrodens (106) | —e | 0.03–0.75 | 0.25 | 0.5 | 100, 0, 0 | 0.12–8 | 1 | 2 | 92, 7, 1 |
| P. intermedia (34) | Nonselective blood agar | 0.016–8f | 0.016 | 1.5 | 68, 0, 32g | 0.016–24h | 0.25 | 12 | 79, 15, 6i |
| P. nigrescens (21) | Nonselective blood agar | <0.016–8j | <0.016 | 2 | 67, 0, 33k | 0.023–24 | 0.125 | 12 | 67, 29, 5 |
| P. intermedia (21) | Blood agar with amoxicillin | 0.25–12f | 2 | 4 | 0, 0, 100g | 0.047–16 | 1.5 | 12 | 76, 14, 10 |
| P. nigrescens (9) | Blood agar with amoxicillin | 0.5–3j | 1 | 3 | 0, 0, 100k | 0.094–16 | 6 | 16 | 44, 44, 12 |
| P. nigrescens (3) | Blood agar with tetracycline | <0.016–2 | 1.5 | 2 | 33, 33, 33 | 6–8 | 6 | 8 | 0, 100, 0 |
| P. intermedia (10) | Blood agar with tetracycline | 0.016–8 | 0.38 | 6 | 40, 0, 60 | 1.5–16h | 6 | 12 | 40, 50, 10i |
50% and 90%, MICs at which 50 and 90% of the isolates tested, respectively, are inhibited.
Data represent the percentage of isolates with a MIC corresponding to the interpretive categories of susceptible, intermediate, and resistant, respectively.
The interpretive categories for E. corrodens were adopted from the interpretive standards of ampicillin and tetracycline susceptibilities for Haemophilus spp. outlined by the National Committee for Clinical Laboratory Standards: MICs of ≤1, 2, and ≥4 μg of ampicillin per ml and ≤2, 4, and ≥8 μg of tetracycline per ml.
The interpretive categories for P. intermedia and P. nigrescens were adopted from the interpretive standards of ampicillin and tetracycline susceptibilities for anaerobic bacteria outlined by the National Committee for Clinical Laboratory Standards: MICs of ≤0.5, 1, and ≥2 μg of ampicillin per ml. All β-lactamase-positive isolates were considered resistant, and MICs of tetracycline were ≤4, 8, and ≥16 μg/ml.
—, most of the E. corrodens isolates were recovered in primary cultures on blood agar plates with 1 μg of clindamycin per ml.
f,h,j Statistically significant difference between selective and nonselective medium at P < 0.01 by Mann-Whitney test.
g,k P < 0.0001 by chi-square test between selective and nonselective medium.
P < 0.05 by chi-square test between selective and nonselective medium.